Preinfusion: basic principles, preinfusion on a Decent, and PCT ratio

This article is based on research and a presentation by Stéphane Ribes from May 2019.

1. Introduction

Ideal preinfusion involves the rapid and uniform wetting of ground coffee grinds to establish consistent puck compression, thermal homogeneity, and fluid velocity prior to main extraction. Traditional single-direction water delivery methods often fail to achieve this uniformity. Utilizing the Decent Espresso (DE1) platform, this research by Stéphane Ribes (May 2019) investigates how altering preinfusion flow rates (0.5 mL/s to 8.0mL/s), pressure transition thresholds, and multi-step preinfusion profiles impacts physical puck behavior, extraction dynamics, and the Puck Contact Time (PCT) ratio.

2. Summary

From the brewing perspective, a more even preinfusion improves coffee extraction and taste.

In the traditional espresso process where water hits the coffee puck from only 1 direction, with no stirring possibilities, targeting a perfect preinfusion is obviously a challenging objective!

We have assessed the influence of the water flow during espresso preinfusion, considering the following characteristics:

What's presented here is a mix of basic observation results and hypotheses based on expected physical phenomena.

With the Decent Espresso machine, espresso preinfusion can easily be adjusted and perfected.

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3. Questions asked

How does the preinfusion flow rate influence post-preinfusion puck density uniformity and total extraction flow resistance?

What physical parameters dictate the homogeneity of contact time and temperature between the top and bottom layers of the coffee bed?

What causes post-extraction surface cratering, and how can preinfusion parameters mitigate it?

How can a multi-step, variable-flow preinfusion profile optimize overall extraction consistency?

How is the Puck Contact Time (PCT) ratio defined, calculated, and mathematically balanced?

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4. Method

Equipment & bed metrics: Tests were conducted using a Decent Espresso DE1PRO v1.1 machine and an 18g filter basket loaded with a 20g coffee dose (occupying 30cm³ tamped volume and requiring 40mL of water for complete preinfusion).

Evaluated flow rate categories:

Very low flow: 0.5–1.5 mL/s.

Low-medium flow: 1.5–3.0mL/s.

Medium-high flow: 3.0–5.0mL/s.

High flow: 5.0–8.0mL/s.

Puck Contact Time (PCT) modeling: Residual brew water volume was defined as approximately 1mL per 1g of dry coffee dose. Top and bottom contact durations were evaluated across brew ratios from 1:1 (20g yield) to 1:3 (60g yield).

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5. Proceeding

Target equilibrium ratio = 1.0.

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6. All the experiments

6.1. Even puck density

During preinfusion with a quick pressure increase, the bottom layers of the puck are more compressed.

The puck density is more homogenous when a slow preinfusion is performed.

This explains why, with the same grind size, dose and extraction pressure (e.g. 9 bar), higher flow rates during preinfusion induce lower flow rates during extraction (with longer preinfusion a finer grind is needed to get similar flow during extraction).

Higher puck density -> less available space around the coffee particle

In the case of a quick preinfusion, the fluid velocity is higher around the coffee grinds at the bottom of the puck. The resulting shorter contact time suggests a lower extraction of the coffee grinds from the bottom of the puck. This could also contribute to increase the likelihood of messy sprays that can sometimes be seen at the exit of the basket, especially when combined with high extraction flow rates.

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6.2. Even contact time & temperature

With the Decent Espresso machine, a 20g coffee dose requires ca. 40mL of water to perform full preinfusion (DE1 PRO v1.1 machine – 20g of coffee in an 18g basket).

With a 1ml/s preinfusion, when the coffee grinds at the bottom of the basket get wet, those from the top of the puck have already been soaked in hot water for 40 seconds!

This additional contact time of the top grinds will be partly (or even fully) compensated at the end of the extraction when the last amount of brewed coffee will pour out of the basket. This amount corresponds to the volume of residual fluid in the puck in the last stages of the extraction.

The ideal balance (same contact time for top and bottom grinds) is obtained when the time to pour the residual brew water equals the preinfusion time.

This can be achieved thanks to appropriate selection of flow rates for preinfusion and for the (last step of the) extraction phase.

The volume of a 20g coffee dose (dry grinds), tamped in a 58mm basket, is more or less 30cm³.

Around 20ml of water suffice to saturate this amount of grinds.

Let's consider a typical 1:2 brew ratio to get 40ml of coffee in the cup.

In this example with the chosen brew ratio of 1:2, “Extraction” water only pushes down the preinfusion water through the puck; it is not actually used as brewing water (also valid for lower brew ratios).

Considering a constant flow extraction phase and our 20g coffee dose, the contact time of the coffee grinds with water are:

Top of the coffee puck -> preinfusion time + extraction time – time to pour the last 20ml (1)

Bottom of the coffee puck -> pouring time (once preinfusion is complete)

In this example (DE1 v1.1 & 20g of coffee in an 18g basket), with a constant flow rate during extraction, preinfusion should be roughly twice shorter than the extraction phase to get an even overall contact time for all coffee grinds.

On top of contact time differences along the height of the puck, the brew temperature varies significantly within the coffee puck. Identified influencing parameters are:

Higher brew ratios are positive as they smoothen the phenomenon.

Longer preinfusion and extraction increase the thermal losses and decrease the actual brewing temperature (hence have detrimental effect on temperature evenness).

Also, as coffee gets extracted, the resulting fluid gets more concentrated in extracted compounds which makes it less efficient than pure water to perform further extraction. The consequence, again, is a lower extraction of the coffee grinds from the bottom of the puck.

As for temperature unevenness, this effect becomes less visible when the brew ratio increases.

Unclear impact (if any) of preinfusion and extraction flow rates on this phenomenon.

Increasing the brew ratio from 1:1 to 1:3 halves the temperature gap between top and bottom grinds.

However, as extraction efficiency decreases with time, the actual benefits in the cup are presumably lower than those suggested by these average gap values.

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6.3. Even puck surface after preinfusion

Once extraction is complete, craters can sometimes be observed on the surface of the coffee puck.

The exact root cause of these craters is not fully clear but trying to avoid them seems a reasonable objective, as they reveal that channeling has probably occurred during extraction.

As far as the generation of craters is concerned, the very beginning of the preinfusion phase is probably one of the most critical moments: it can be assumed that water droplets hitting repeatedly the same spot of the top of the puck could create this kind of surface unevenness.

To mitigate the risk of generating craters at the beginning of the preinfusion, one can recommend to avoid too high or too low preinfusion flow rates:

With high flow rates (> 5 mL/s) water will obviously hit the surface with more energy.

With very low flow rates (< 1 mL/s), water distribution above the puck may be suboptimal.

A moderate speed of pressure increase after PI has also proven to reduce the occurrence of craters.

Other actions not linked with the preinfusion flow rate (e.g. puck preparation, headspace, shower screen cleanliness & type) to avoid puck craters & channeling in general, have not been analyzed.

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Espresso preinfusion: How to make it more decent

With the Decent Espresso machine, the preinfusion process can easily be modified to benefit from the best of each flow rate family and improve the overall preinfusion performance.

With the Decent Espresso machine, on top of the possibility to select any flow rate value to perform preinfusion, a 2-step approach can further improve the consistency of the process: medium high flow rate first, followed by a lower flow rate phase.

A moderate high flow rate at the very beginning of the preinfusion reduces the overall preinfusion time and hence improves the Puck Contact Time homogeneity (avoids too high PCT ratio).

Low flow rate in the second preinfusion step limits puck compression and a too steep pressure increase once preinfusion is complete.

The switch between the 2 preinfusion steps can easily be triggered by a pressure threshold (typically around 1 bar).

If the most even preinfusion is the target (and hence the most even overall extraction) it is also possible to adjust all preinfusion and extraction parameters (flow rates, thresholds) taking into account the proposed chart (see table "Best suggested settings to reach even Puck Contact Time and temperature").

Impacts of other parameters (e.g. dose, puck preparation, headspace) will be quantified and discussed in a future study.

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Advanced Decent preinfusion

Advanced preinfusion with a standard Flow profile (1/2)

Standard Flow profile (2/2)

For a Pressure priority shot, an advanced profile is needed.

Exit pressures of steps 1 and 2 can be adjusted to reach optimum preinfusion time.

An additional step between stages 2 and 3 could be imagined (e.g. pressure ramp to ensure smoother transition).

Trials to replace step 2 by a pressure priority phase (e.g. 1 bar) have not been very successful (hard to get smooth transitions between flow and pressure priority modes).

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How good is your Puck Contact Time (PCT) ratio?

PCT ratio Formula:

PCT ratio = ECTT / ECTB

ECTT (Excess Contact Time of Top grinds): Preinfusion time * ECTB (Excess Contact Time of Bottom grinds): Time to pour the “residual brew water”.

Residual brew water volume = more or less 1 mL / g of dry coffee (dose) (2)

Target for PCT ratio = 1

PCT ratio < 1: too short preinfusion

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7. Results, summarized

Puck compression & flow mechanics: High preinfusion flow rates (and rapid pressure rises) compress bottom puck layers more heavily, creating higher fluid velocities around bottom grinds and lower subsequent extraction flow. Slower preinfusion provides uniform puck density, lowering peak pressure for identical grinds and requiring a finer grind setting to match flow.

Channeling risks: Combining a high preinfusion flow rate with a steep pressure ramp (3.7 bar/s vs. 1.5 bar/s) significantly increases the incidence of puck channeling.

Thermal & contact time gradients: Slow preinfusion (1mL/s) leaves top grinds soaked for 40 seconds before bottom wetting occurs. Thermal gradients are severe in short shots; expanding the brew ratio from 1:1 to 1:3 reduces the top-to-bottom average temperature gap from 28°C to 14°C.

Surface integrity: Puck craters are induced by initial flow rates that are too high (5mL/s, high kinetic impact) or too low (<1mL/s, suboptimal shower screen distribution), or by aggressive post-preinfusion pressure jumps.

Two-step preinfusion benefits: A variable preinfusion (medium-high initial flow followed by a low flow step triggered at 1 bar) maximizes contact time uniformity while keeping puck compression low and preventing pressure spikes.

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8. Conclusion

In conclusion, the questions brought up under the chapter "Questions" can be answered as follows:

How does the preinfusion flow rate influence post-preinfusion puck density uniformity and total extraction flow resistance?

Rapid preinfusion compacts the lower puck layers, decreasing interstitial space, elevating fluid velocity at the base, and increasing overall extraction resistance. Slower preinfusion maintains uniform bed density, requiring a finer grind size to achieve equivalent extraction pressure and flow.

What physical parameters dictate the homogeneity of contact time and temperature between the top and bottom layers of the coffee bed?

Contact time balance is governed by matching the preinfusion duration to the time required to pour the residual brew water volume. Temperature uniformity is primarily driven by brew ratio (higher ratios like 1:3 reduce thermal gaps by half compared to 1:1) and shorter shot durations that limit heat loss.

What causes post-extraction surface cratering, and how can preinfusion parameters mitigate it?

Surface craters stem from high-energy water impact at excessive flow rates (>5mL/s), poor surface distribution at very low flow rates (<1mL/s), or steep pressure ramps post-preinfusion. Moderate initial preinfusion flow rates (1.5–5.0mL/s) and smooth pressure transition ramps mitigate crater formation.

How can a multi-step, variable-flow preinfusion profile optimize overall extraction consistency?

Initiating preinfusion at a medium-high flow rate (3.0–5.0mL/s) saturates the puck quickly to minimize top-to-bottom contact gaps. Transitioning to a lower flow rate upon reaching a 1 bar exit threshold prevents excessive puck compression and avoids steep pressure spikes prior to extraction.

How is the Puck Contact Time (PCT) ratio defined, calculated, and mathematically balanced?

The PCT ratio is defined as ECTT / ECTB. It is calculated by dividing total preinfusion time by the time needed to pour the residual brew water (1mL per gram of dry dose divided by final extraction flow rate). A ratio of 1.0 represents ideal, balanced contact time across all puck layers; values below 1.0 indicate insufficient preinfusion duration.

(1)Probably slightly less if puck erosion was considered (not taken into account here)

(2)Probably slightly less if puck erosion was considered (not taken into account here)

It's almost a blind basket: A first step to better understand a pressure curve during espresso

This article is based on research by Stéphane Ribes, from a presentation in June 2019, which you can find here.

1. Introduction

Pressure during espresso extraction is not determined only by the resistance of the coffee puck. Rather, the compression of the air trapped above the puck is a major factor governing the initial pressure curve. Three variables determine this compression: the initial headspace (1), the water flow supplied by the pump (2), and the water flow entering the coffee puck (3).

Considering a perfect gas model, the following formula can be established:

Blind-basket experiments with a DE1PRO showed acceptable agreement with this model.

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2. Questions asked

The following questions can be inferred from Ribes' presentation:

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3. Method

Tests were carried out with a DE1PRO v1.1 Decent Espresso machine. Blind-basket experiments isolated the effects of headspace and pump flow. Headspace was varied by adding water to the blind basket, producing estimated air volumes of 36, 26, 16 and 10 cm³.

Flow-rate experiments used initial rates of 1.0, 1.5, 2.0 and 4.0 mL/s. In these tests, water flow was switched to 0 mL/s when pressure reached 7 bar.

Coffee-puck experiments used 12 g in a 15 g VST basket, an IMS SI 200 IM shower screen, and EK43 grind settings from 0.9 to 1.2. Further practical comparisons investigated different basket sizes and IMS CI 200 versus SI 200 shower screens.

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4. Proceeding

First, the blind basket was used to determine how changing the trapped air volume alters pressure build-up independently of coffee. Second, the pump flow was varied while headspace remained comparable. Third, coffee was introduced to separate the effect of water entering the puck from the effect of puck resistance itself. Finally, basket size and shower-screen configurations were changed to examine whether these principles also explain differences observed in realistic espresso preparations.

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5. Results

5.1. Effect of headspace

The graph below shows a clear positive relationship between headspace and the time required to reach 7 bar at 1 mL/s.

Approximately 10 cm³ required 15 s, 16 cm³ about 21 s, 26 cm³ about 28 s, and 36 cm³ about 32 s. Thus, a smaller trapped air volume is compressed more rapidly and causes pressure to rise sooner and more steeply.

In other words, as headspace decreases, the time required to reach 7 bar at 1 mL/s decreases significantly.

5.2. Effect of water-flow rate

The inverse relationship with flow rate is even stronger. The time to 7 bar fell from roughly 32 s at 1 mL/s to 23 s at 1.5 mL/s, 17 s at 2 mL/s, and only 9 s at 4 mL/s. Higher flow also produced progressively greater pressure overshoot after the 7-bar shut-off trigger, showing that the hydraulic system continues to respond after pump flow is stopped.

In other words, higher input water flow rates significantly reduce the time needed to reach 7 bar. Also, more pressure overshoot occurs as the input water flow rate increases.

5.3. Effects of grind size and puck penetration

Changing the EK43 setting from 0.9 to 1.2 produced a large decrease in maximum extraction pressure, from approximately 12 bar to 3–4 bar. In contrast, the additional time needed to reach 3 bar compared with the blind basket stayed close to 4.5–5.0 s. An excessively fine grind produced a pressure curve resembling the corresponding blind-basket curve, shifted later in time. Most of this initial delay was due to water entering the coffee puck rather than to grind-dependent hydraulic resistance.

This supports the principal observation that, during relatively slow preinfusion, the pressure-rise delay caused by puck saturation is only weakly affected by grind size.

5.4. Effect of basket size

With the same 18 g dose and EK1.8 grind, changing from a VST 20 g basket to the taller VST 22 g basket increased headspace. The measured additional pressure-rise delay increased from about 5.0 to 7.5 s, while maximum extraction pressure decreased. Despite the different pressure curves, both examples reported an extraction yield of 19.9%.

5.5. Effect of different shower screens

With a 15 g dose in the same basket, changing from the IMS CI 200 to SI 200 screen had little effect on headspace and therefore little effect on the pressure delay: approximately 6.0 versus 5.5 s. Extraction yields were 20.4% and 21.3%, respectively. The SI 200 produced a gentler pressure decline; the proposed explanation is its smaller distance to the puck surface, although further testing is needed to confirm this hypothesis.

In a second comparison, changing simultaneously from CI 200 + VST 15 g to SI 200 + VST 20 g, with an 18 g dose and the same EK1.8 setting, increased the time to 2 bar from 14 to 16 s. The lower maximum pressure was attributed to the combined effect of increased headspace and the larger holes of the VST 20 g basket.

5.6. Main Observation Results:

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6. Conclusion

The experiments indicate that the early espresso pressure curve can largely be interpreted as the compression of a trapped air volume by the net accumulation of water above the puck. Headspace and pump flow determine how rapidly this compression occurs, while water entering the coffee delays it. Basket geometry therefore affects pressure indirectly through its effect on headspace.

1. How does initial headspace influence pressure build-up?

A smaller headspace produces an earlier and faster pressure increase. Increasing headspace substantially delays the pressure rise.

2. How does pump water-flow rate influence the pressure curve?

Higher flow produces a much faster pressure increase. It also increases pressure overshoot when flow is stopped at a fixed pressure threshold.

3. How do puck penetration and grind size influence the initial delay?

Water entering the puck delays pressure development by roughly 4.5–5 s in the experiments. Grind size strongly changes maximum extraction pressure but has comparatively little effect on this initial delay during slow preinfusion.

4. How do basket size and shower-screen configuration affect the pressure profile?

Basket size can substantially change headspace and therefore pressure timing. Changing the shower screen alone has relatively little effect when headspace remains similar, whereas configurations that increase headspace produce a later rise and generally lower maximum extraction pressure.

Radial uniformity of espresso extractions

1. Introduction

Stéphane Ribes's March 2020 presentation, Radial Uniformity of Espresso Extractions, investigates whether coffee is extracted evenly across the radius of an espresso puck. Instead of treating the extraction yield of the finished beverage as a complete description of the shot, the presentation separates the spent puck into concentric regions and measures the extraction yield of its centre, middle and outer portions.

This distinction matters because a satisfactory average extraction yield can conceal substantial internal variation. A highly extracted centre can compensate numerically for a severely underextracted perimeter. The presentation therefore focuses on both:

Overall espresso extraction yield, measured from the beverage.

Local puck extraction yield, measured separately in concentric regions of the coffee bed.

Two practical interventions are compared: placing a V60 paper filter below the puck and changing the tamper from a flat base to a convex “US curve” base. The presentation then proposes a basket-design explanation for the remaining edge deficit.

The central finding is that, under the tested conditions, the perimeter of a conventional espresso puck is much less extracted than its centre. A paper filter below the puck substantially reduces this radial difference, whereas a convex tamper base makes it worse.

2. Questions asked

Stéphane attempted to investigate and answer the following questions:

In a standard espresso shot without a paper filter below the puck, how uniform is extraction yield from the centre to the edge?

Does placing a V60 paper filter below the puck improve radial extraction uniformity and increase the average extraction yield?

How does a convex “US curve” tamper base affect radial extraction compared with a flat tamper base?

Could the limited perforated area of an espresso basket explain peripheral underextraction, and would enlarging that area be a promising solution?

3. Method

Experimental principle

The test protocol proceeds along two analytical paths. First, the espresso beverage is collected and its overall extraction yield is determined. Second, the puck is divided into three concentric portions: outside, middle and centre. The EY of the three puck fractions is then also determined.

The radial graphs identify the boundaries of the three regions as follows:

Equipment and controlled conditions

Equipment & tools: Decent Espresso Machine DE1PRO v1.1 (with a red Cafelat 8.0 mm silicone gasket and an IMS SI 200 IM screen without spacer), Mahlkönig EK43 S grinder fitted with SSP "High Uniformity" burrs, and a 15g VST ridgeless filter basket.

Water & coffee preparation: Montille water adjusted to 50 ppm CaCO₃ alkalinity and 125 ppm CaCO₃ total hardness using sodium carbonate and Epsom salts. Single doses of frozen coffee beans (12g per shot) were ground into a double-walled stainless steel cup.

Puck prep & tamping: The basket and shower screen were dried with a clean tissue before every shot. Distribution was performed using a Londinium WDT tool with a Decent funnel (no vertical tapping), followed by gentle raking with a hog tool to smooth the surface. Tamping was completed using The Force Tamper (58.5 mm smooth flat or US curved base) applied twice sequentially.

Measurements: Samples were extracted, divided into radial zones (center, middle, outside), and evaluated along with the final espresso shot. Total Dissolved Solids (TDS) and Extraction Yield (EY) were measured at room temperature using an unfiltered Atago PAL refractometer (zeroed with the test water) after vigorous stirring. Each recorded data point represents the average of 3 to 5 measurements.

For the filter and tamper comparisons, the dose, basket, grind setting and 1:2.5 ratio were held constant. This makes the comparisons meaningful at one common grind resistance, although it does not show how each configuration would perform if individually re-dialed to its own optimum.

Extraction profile

The presentation supplies a hybrid “lever-blooming” profile described as a combination of Londinium and blooming profiles. Its principal extraction flow is 2.5 mL/s. Here's the profile steps:

The initial “lock portafilter” step is optional. Its purpose is to keep the puck from being exposed to the hot machine environment while the brew water completes its final warm-up.

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4. Results

Thanks to his experiments, Stéphane found the following EY:

To sum it all up, Stéphane found the following:

5. Conclusion

The presentation's evidence points to a specific structural weakness in conventional espresso extraction: the outer part of the puck receives substantially less effective extraction than the centre. This is not a minor border effect, because the affected outside annulus represents approximately one quarter of the dose.

The V60 paper filter below the puck is the most successful tested intervention. It leaves the centre essentially unchanged while raising the outer-region extraction from 13% to 22%, reducing the radial spread by three quarters and increasing overall extraction from 21% to 24%. In contrast, the convex tamper intensifies central preference and reduces outer extraction to only 7%.

The basket-perforation analysis provides a coherent engineering explanation, but it remains a proposal requiring a direct experiment.

1: In a standard espresso shot without a paper filter below the puck, how uniform is extraction yield from the centre to the edge?

It is highly nonuniform under the tested conditions. The centre reaches 25% EY, the middle 23% and the outside only 13%. The outer quarter of the dose is therefore extracted at only about 52% of the centre's level. The reported 21% beverage average conceals a 12-percentage-point radial range.

2: Does placing a V60 paper filter below the puck improve radial extraction uniformity and increase the average extraction yield?

Yes, substantially in this experiment. The outside rises from 13% to 22%, while the middle rises from 23% to 24% and the centre remains at 25%. The centre-to-edge range contracts from 12 to 3 points, and the overall extraction yield increases from 21% to 24%. The improvement is driven mainly by recovery of peripheral extraction rather than by further extraction of the centre.

3: How does a convex “US curve” tamper base affect radial extraction compared with a flat tamper base?

It worsens radial uniformity. The centre remains at 25%, but the middle falls to 22% and the outside falls to 7%. The centre-to-edge difference grows from 12 to 18 points, and the reported overall extraction declines from 21% to 20%. The data are consistent with flow being concentrated more strongly toward the centre at the expense of the puck perimeter.

4: Could the limited perforated area of an espresso basket explain peripheral underextraction, and would enlarging that area be a promising solution?

It is a plausible and geometrically well-supported hypothesis, but it is not proven by the presentation. A standard 49 mm perforated field ends almost exactly where the underextracted outer region begins, and the 40 mm Reneka field is considerably smaller. Increasing the perforated diameter from 49 to 53 mm would add approximately 17% active area and extend the holes into the measured outer annulus. A controlled basket experiment would still be necessary to separate the effect of perforated diameter from hole density, hole shape, basket geometry and other design differences.

The 4 mothers: a unified theory of espresso making recipes

The optimal espresso curve

I've been working on a "unified theory of espresso making recipes", which results in 4 "mother" recipes.

But before I plunge into that, I want to make the argument that there is an arguably optimal pressure curve for espresso recipes.

You can see it as the pressure profile that occurs naturally when constant flow water is used to make an Allongé recipe coffee on the Decent. The resulting pressure is a reflection of the declining puck resistance over time, as the puck loses material to the espresso drink.

This curve has the following characteristics:

a preinfusion that takes about 10 seconds before pressure builds

a peak pressure around 8.6 bar

an end pressure around around 4 bar

a total espresso making time around 30 seconds

I think it's no coincidence that this is exactly the pressure curve that most spring lever espresso machines naturally give you.  The people who designed their machines, very likely did this on purpose, by using their eyes and taste buds, as they didn't have access to the data we now have.

I'm going to argue that the "best" espresso recipes are all variations on the curve above, as they recognize the reality of the physics of the coffee puck during espresso extraction.

For me, "best" = "tastes most pleasing" = "most good flavors, minimizing bad flavors". I realize that people have different levels of acidity they seek, and I'm deliberately putting that aside here, focussing instead on flavors.

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The "four mother" recipes

My position is: a bean's roast level is the most important consideration in choosing a recipe for making espresso.

This is because, the darker a coffee bean is roasted:

Put another way: the less soluble a bean is, the more your recipe will have to work harder to get material out of the bean.

The three main ways to get more material out of a bean are:

Finer grind size also increases extraction, but is not an independent variable. There is typically an appropriate grind size for each type of recipe.

This gives us:

Which gives us these insights:

Classic Italian espresso machines are hard-wired to give their best results with Italian-style roasted beans (medium dark to dark).  FYI: I consider the common "flat 9 bar" profile to be a simplified (and less good) version of the Lever profile.  Lever Profile results in typical extraction yields of 19% to 21%, that are the lowest of the 4 recipes, since flow rate is lowest and water contact time is the shortest, with this recipe.

Light roasts are known to fall apart quickly and channel during espresso making when using the Lever (or flat 9 bar) profile. This is likely why those whose machines can only do that recipe of espresso will tend to compensate by either making Ristretto (short time) shots, or putting a lot more coffee into the basket.  If you don't do this, you get very acidic, generally under-extracted espresso, because you haven't appropriately compensated for the lower solubility of the beans you're working with.

The Blooming recipe works well on medium to light roast beans, but with ultralight roasts, the puck tends to fall apart at the end of Blooming shots, as ultralight beans don't have enough puck integrity to survive the last stage.  Rao tries to work around this by having the last stage flow profiled, so that if the puck integrity fails, at least the flow rate doesn't go super-fast. The long preinfusion demands a super-fine ground.  Blooming results in the highest extractions, both because of the long water contact time, but also because this recipe requires the finest ground beans, which also increases extraction.

The Allongé recipe works best with ultralight roasts because it demands so little puck integrity, and the fast flow rate require coarse grounds in order to not go over-pressure.  The Allongé recipe follows the findings from the widely quoted Hendon research paper https://www.sciencedirect.com/science/article/pii/S2590238519304102 that coarse grinds, and fast flow, result in relatively high extractions and good consistency. The typical EY of 21%-23% is likely due to the coarser grind than Blooming. But because Hendon didn't use a flow-profiling or pressure profiling espresso machine, his espresso suffered from rapid loss of puck integrity, and so he ended up advocating for shorter duration espresso recipes.  By using constant flow (or decreasing pressure) it's possible to use the coarse grind/fast-flow approach but to pull the shot to the normal 30 second duration.

Each recipe has an ideal bean roast level.  If you use dark roasted beans for any non-lever recipe, you'll likely over-extract it.  Light beans on Lever will often under-extract and/or channel.

People with manual lever machines are able to make all these recipes, and have long been able to make delicious espresso with light roasted beans.  Typically, this has been either a Blooming shot, or they've cleverly made 50 seconds Lever profile shots, thus extending the water contact time over the entire duration of the recipe.

Roast Levels

My definition of roast levels is flavor based, which isn't necessarily that common an approach but here is how I think of them:

dark roast: dark chocolate flavor, some "burnt forest" flavors. Often served very thick.  Taste profile similar to dark baking chocolate.

medium-dark: a mix of chocolate flavors, both dark and medium, with little (if any) burnt flavors, and some layering of different styles of chocolate.

medium: less dark chocolate flavors, but no burnt flavors.  Can include layers of different chocolate roast level flavors.

medium-light: same as medium (layers of chocolate), but with some fruity (tropical and red fruits are typical) or floral notes added as well. Can have a "milk chocolate" flavor.  Taste profile is similar to expensive "single origin chocolates".

light: no chocolate flavors. A "well developed" light has other Maillard/Caramelization flavors such caramel, toffee, dulce-de-leche, cooked pear. A "less developed" light roast will not have any flavors arising from caramelization. Fruit, floral, meat, and more. An amazing panorama of flavors is possible with light roasted beans, which is why so many coffee experts favor this roast style.

ultralight: intense fruit flavors, intense flowers.  Often tastes more like expensive tea than traditional coffee.

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This article is a work in progress, and represents my current thinking. I very much would like to discuss it and you're welcome to revise my chart above with your ideas.

The Hog puck preparation tool

The following article is based on a presentation by Stéphane Ribes from June 2019. It's based on research with the so-called Hog puck preparation tool. In fact, this study evaluates how the Hog tool impacts extraction dynamics, flow profiles, temperature and concentration gradients, and taste across different extraction profiles.

What is the Hog?

Introduced conceptually by Matt Perger of Barista Hustle in 2017, "The Hog" is a specialized puck preparation tool designed to introduce "controlled channeling" by poking vertical canals into the compressed coffee puck prior to tamping. So it's not a WDT distributor tool like we know it today. Rather, it's actively used to poke holes into the coffee puck and, thus, control the channeling.

The 2 hog tools tested were inspired by this work; they were designed and manufactured by Joachim Morceau (and his wife), French barista – formerly head Barista at Terres de Café and now owner of the Substance café specialty coffee place in Paris.

A similar, now available tool, is the PorcuPress by Sworksdesign.

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Benefits

Reduced edge channeling

Quicker wetting of the coffee puck -> More even preinfusion & extraction

reduced temperature gap between top and bottom grinds

lower concentration gradient of the extracting fluid between top and bottom grinds

reduced negative impacts of slow preinfusions

less puck compression with high preinfusion flow rates

More stable pressure (flow profile with constant flow)

Smoother evolution of the extraction yield -> better control of the extraction in the typical range of brew ratio, when reaching the highest possible extraction is not the most desirable objective

Additional information

Requires a finer grind

Represents an additional step in the puck preparation (does not replace grinds distribution)

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Questions asked

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Tools used

Espresso machine: Decent Espresso DE1PRO v1.1 fitted with an IMS SI 200 IM shower screen.

Grinder: Mahlkönig EK43 S.

Puck preparation tools:

The Hog: 95 steel spikes embedded in a 3D-printed base for 20g+ VST baskets, designed and manufactured by Joachim Morceau. Tested in two variants:

Thin Hog (0.8 mm diameter spikes) and

Thick Hog (1.1 mm diameter spikes).

Hog stand: Used during pressure tests to ensure precise, straight vertical insertion and withdrawal.

Other prep: Mini whisk (for WDT in cup and basket), 58.6 mm manual tamper, 22g VST basket.

Filter paper (flow tests): 55 mm Camlab paper filters placed at the bottom of the basket (omitted during 9 bar pressure tests).

Measurement & water:

Atago PAL refractometer for TDS/EY measurements.

Montille water (low mineral), re-mineralized to SCAA standards with sodium carbonate and Epsom salts for pressure-priority testing.

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Method / proceeding

Single-origin beans (The Barn La Laja for flow tests; Friedhats Kochere Boji & Las Margaritas for pressure tests) were vacuumed, frozen, and ground frozen in a double-wall stainless steel cup.

Dose: 19g (flow tests) or 18.5g targeting 42g out (pressure tests) into a 22g VST basket.

WDT performed in the cup and basket using a mini whisk.

The Hog tool was pressed straight down into the un-tamped bed and pulled directly back out.

Gentle surface raking (no tapping) followed by manual tamping with a 58.6 mm tamper.

Flow priority profiles: 2.5 mL/s constant flow rate with bottom paper filter. Sliced extractions were performed where the output was split into 10 distinct portions (every 4 seconds post-first-drop) to track gradual extraction yield evolution.

Straight 9 bar pressure ("E61 Classic"): Performed without bottom paper filter.

Advanced preinfusion + 9 bar pressure: Performed without bottom paper filter.

Pressure/flow curve logging via the Decent DE1PRO interface.

Refractometer measurements (TDS/EY averaged over 3–6 readings per sample at room temperature).

Sensory/taste ratings on a subjective scale comparing acidity, sweetness, and astringency.

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Observed impact of the Hog on extraction

Effects of the hog tool on pressure evolution during espresso extraction (flow profile)

Grind setting was adapted to reach a comparable pressure peak during extraction

Much finer grind is needed with the "thick Hog" (EK1.5, from EK2.2 with no hog)

Quicker wetting of the coffee puck with hogs, earlier first drop in cup

First drop in cup with hogs: 12 s

Without hog: 14 s

Slower rates of pressure rise and decrease with hogs – more stable overall extraction pressure

Intermediate intensity of all recorded effects with the thinner spines

Effects of the hog tools on extraction evolution

Flow profile, 19 gram dose

For each shot, the output was split into 10 portions (every 4 s after first drop)

Thanks to the flow priority extraction (2.5 mL/s), all samples had comparable volumes

Coffee extraction is performed more gradually with the hogs

Typical brew ratio zone: (2.1 – 2.6)

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The Hog: Straight 9 bar extraction experiment without paper filter

Tested configurations

No hog tool – EK2.3: EY 19.8%

Thin hog – EK2.3: EY 19.3%

Thick hog – EK2.3: EY 19.0%

Observation and measurement results

Slightly delayed pressure rise but no visible impact on the extraction time

Altered flow evolution in the cup: higher flow rate first, then lower flow

Less turbulences and sprays at the exit of the basket

Lower extraction yield

All these effects are more intense with the "thick" hog (1.1 mm spines)

The Hog: Advanced preinfusion and 9 bar extraction experiment without paper filter

Tested configurations

No hog tool – EK1.6: EY 19.8%

Thin hog – EK1.6: EY 19.5%

Thick hog – EK1.6: EY 18.7%

Thick hog – EK1.45: EY 19.0%

Observations

Also...

Lower extraction yield

All these effects are more intense with the "thick" hog (1.1 mm spines)

Summary table comparing taste

Conclusion

Creating vertical canals in the coffee bed via the Hog preparation tool acts as a mechanism of "controlled channeling" that fundamentally changes how water interacts with the coffee puck. Based on the findings of the experiments, the questions elaborated above can be answered as follows:

1. How do vertical canals affect pressure stability, flow dynamics, and puck wetting? Creating vertical canals leads to significantly quicker, more uniform puck wetting, moving the time to first drop from 14 seconds to 12 seconds. The canals reduce edge channeling, lower the temperature and concentration gradients between top and bottom grinds, and minimize puck compression during high preinfusion flow rates. Under flow priority profiles, this reduces the rates of pressure rise and decrease, resulting in a smoother, more stable extraction pressure overall.

2. What is the impact of the Hog tool on Extraction Yield (EY) progression? Instead of a rapid initial spike in extraction, the Hog alters the EY progression to extract coffee more gradually throughout the shot. While overall final extraction yields are slightly lower compared to non-Hog prep at the same grind size, this smoother progression offers better control over extraction in standard brew ratio ranges (e.g., 2.1-2.6), preventing sharp over- or under-extraction spikes early in the shot.

3. What are the key differences between the thin-spike and thick-spike Hog designs? Both designs feature 95 steel spikes set in a 3D-printed base for 20g+ VST baskets, but differ in spike diameter: the "thin" version uses 0.8 mm spikes, while the "thick" version uses 1.1 mm spikes. The thick-spike tool exerts a much stronger effect on puck resistance, requiring a significantly finer grind setting (e.g., EK1.5 vs. EK2.2) to match peak extraction pressure. The thin-spike design offers a more moderate, balanced modulation of pressure and flow without requiring extreme grind adjustments.

4. How does the Hog tool interact with different extraction profiles?

Flow priority: Provides a stabilized pressure curve and a controlled, gradual extraction curve when paired with a bottom paper filter.

Straight 9 bar: Delays initial pressure rise slightly and alters flow rate evolution (higher initial flow, lower late flow), reducing basket exit spray and turbulence.

Advanced preinfusion: Results in earlier first drops and faster overall shot times. A finer grind setting is required to restore target shot timing and yield, particularly when using the thick-spike design.

5. How does vertical canal preparation influence the in-cup taste profile? The Hog measurably improves in-cup flavor profiles by reducing harsh channeling sourness. Across both straight 9-bar and advanced preinfusion profiles, the thin-spike Hog (0.8 mm) consistently produces the best sensory results, significantly enhancing sweetness, clarity, and fruity acidity compared to standard preparation.

Effects of using frozen beans on coffee

Stéphane Ribes explored the impact of freezing coffee beans on espresso extraction consistency, water flow resistance, and optimal resting time post-roast. This article is based on his presentation from July 2019.

Main questions asked

1. Consistency: Does grinding frozen coffee beans lead to more consistent extractions across multiple days using identical parameters?

2. Resistance: How does grinding frozen beans affect water flow resistance during extraction compared to grinding non-frozen beans?

3. Resting time: What is the impact of resting coffee beans for additional days prior to freezing on extraction pressure, extraction yield (EY), and overall taste quality?

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Method used & proceeding

Stéphane conducted controlled experiments measuring extraction yield (EY), extraction pressure profiles, and flavor characteristics across different coffee roasts and resting timelines.

Equipment & preparation details

Espresso machine: Decent Espresso DE1PRO v1.1 equipped with an IMS SI 200 IM shower screen.

Grinder: Mahlkönig EK43 S grinder.

Water: Montille water adjusted to SCAA standards using sodium carbonate and Epsom salts.

Puck Preparation: Beans ground directly into a double-wall stainless steel cup; Weiss Distribution Technique (WDT) applied in cup with a mini whisk; un-wetted 55 mm Camlab paper filter placed at the bottom of the basket; basket WDT with a mini whisk; surface raking with a Hog tool (0.8 mm diameter spikes) using a vertical hog stand; manual tamp with a 58.6 mm tamper.

TDS & EY measurement: Measured with an Atago PAL refractometer zeroed with SCAA water; samples measured at room temperature following thorough agitation, averaging 3 to 4 measurements per data point.

Testing procedure

Consistency test: Pulled single shots daily across several days (July 15, 18, 19, and 20) using a natural Ethiopian Yirgacheffe (Friedhats Coffee Roasters, filter roast called Kochere Boji) frozen 6 days post-roast, holding grind setting, dose (18.5g in a 22g VST basket), and workflow identical.

Resistance test:

Compared back-to-back shots on the same day using non-frozen vs. frozen natural Kenyan coffee (Terres de Café - Chania Estate) at identical grind settings.

Resting time test: Compared consecutive shots of beans frozen at 6, respectively7 days post-roast versus beans frozen after an additional 6 days of resting (12, respectively 13 days post-roast) using natural Kenyan and natural Ethiopian roasts.

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Results

Consistent extractions: Freezing beans resulted in minimal variance in extraction pressure and Extraction Yield across four separate days (EY values: 21.3%, 21.4%, 21.8%, and 22.0%).

Increased resistance to flow: Grinding frozen beans created significantly higher resistance to water flow compared to non-frozen beans, allowing the barista to use a coarser grind setting to achieve the target extraction pressure.

Impact of resting time: Allowing beans to rest an additional 6 days before freezing lowered the peak extraction pressure, slightly increased the Extraction Yield, and yielded sweeter, more pleasant acidity and overall better-tasting espresso.

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Conclusion

The following conclusions can be drawn from the experiments, answering the questions:

1: Does grinding frozen coffee beans lead to more consistent extractions?

Yes. Grinding frozen beans produces highly repeatable extraction pressures and steady Extraction Yields across days without changing grinder settings. This significantly reduces the need to constantly dial in coffee once an optimal recipe is set.

2.: How does freezing affect water flow resistance during grinding and brewing?

Frozen coffee beans offer greater resistance to water flow when ground. Because frozen beans yield higher puck resistance, a coarser grind setting can be used to reach a target extraction pressure, helping bypass grinder performance limitations associated with ultra-fine grind settings.

3.: Does resting coffee beans longer before freezing improve taste and extraction?

Yes. Allowing beans to rest for roughly two weeks post-roast before freezing lowers the extraction pressure peak, boosts extraction yield, and yields superior flavor profiles marked by sweeter notes and pleasant acidity.

Effects of a rippled tamper base on espresso extraction

Introduction

This study from November 2019 by Stéphane Ribes evaluates the performance and extraction characteristics of a rippled tamper base compared to a standard flat tamper base in espresso preparation. Using high-precision espresso equipment, the investigation assesses how tamping geometry influences extraction parameters, flow dynamics, and sensory qualities.

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Research Questions

Does a rippled tamper base improve espresso extraction yield (EY) compared to a traditional flat base?

How does the rippled base affect puck resistance, wetting speed, and extraction uniformity?

Does the surface profile produced by a rippled tamper impact the visual quality (crema), post-extraction integrity of the coffee puck, or sensory attributes in the final cup?

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Methodology

Hardware & equipment: Tests were performed on a Decent Espresso DE1PRO v1.1 machine using a Cafelat 8.0 mm silicone gasket, paired with a Mahlkönig EK43 S grinder (SSP High Uniformity burrs with Silver Knight coating set to EK 1.1). A 58.5 mm "The Force Tamper" was equipped with interchangeable flat and rippled bases.

Shower screens & headspace: Experiments utilized a 3.8 mm brass spacer with two distinct shower screen models: an IMS CI 200 IM screen (3.8 mm protrusion into basket) and an IMS CI 35 WM screen (ca. 5 mm protrusion).

Puck preparation: Shots used single-dosed, frozen beans in a 15g VST basket. Weiss Distribution Technique (WDT) was applied using a Londinium tool and Decent funnel without tapping. The tamper was applied twice consecutively per shot.

Water & extraction profile: Montille water re-mineralized to 50 ppm CaCO3 alkalinity and 100 ppm CaCO3 total hardness was used. The extraction profile combined elements of a Londinium profile and a blooming shot, maintaining a low-pressure bloom to preserve puck integrity prior to pressure ramping.

Profile used: A mix between a Londinium profile and a blooming shot was used (see settings below).

Measurement: Total Dissolved Solids (TDS) were measured at room temperature using an Atago PAL refractometer zeroed with SCAA water, with each data point representing the mean of 3 to 5 readings.

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Proceeding

Consecutive extraction trials were carried out across both screen/spacer setups while keeping the grind size constant.

Puck resistance variations were evaluated directly and compensated for by adjusting dose weights (ranging between 14g, 14.5g, and 15g with output ratios of 1:2).

Flow characteristics (wetting speed, first drop time) and bottomless portafilter extraction uniformity were observed visually.

Extracted shots were measured for TDS and Extraction Yield (EY), followed by sensory evaluation tracking taste score, intensity, body, acidity, sweetness, flavor, bitterness, and astringency.

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Results

Flow & resistance: The rippled base consistently resulted in lower puck resistance. It exhibited quicker puck wetting and earlier first drops, even when dose weight was increased to compensate for resistance drops.

Extraction yield: The rippled tamper base produced a slight but consistent increase in Extraction Yield of approximately +0.5% to +1.0%. Across tested variations, flat bases yielded between 18.2% and 18.7% EY, whereas rippled bases yielded between 19.0% and 19.3% EY.

Visual & structural features: No observable improvements were detected in extraction uniformity via bottomless portafilter analysis. Shots using the rippled base produced slightly less crema. Post-extraction inspection revealed no impact on puck dryness or compactness.

Sensory assessment: Espresso prepared with the rippled base rated lower in taste scores. Sensory profiles indicated higher perceived astringency and reduced acidity compared to shots tamped with a flat base.

To be more precise, the sensory testing of the coffee made with the flat vs the rippled tamper base revealed the following results:

Taste assessment & profile

Lower acidity: The rippled tamper base consistently produced shots with noticeably lower acidity intensity across all shower screen setups compared to the flat tamper base.

Higher astringency: Shots prepared with the rippled base exhibited higher levels of astringency compared to the flat base.

Body, sweetness, & bitterness: Body, sweetness, flavor, and bitterness intensities remained relatively similar between the two base types across setups.

Overall taste score

Flat tamper base: Received consistently higher overall taste scores (clustering around ~6 to ~7 out of 10).

Rippled tamper base: Received lower overall taste scores (clustering around ~4 to ~5 out of 10).

In summary, despite yielding slightly higher extraction yields, the rippled base resulted in less favorable espresso shots due to increased astringency and muted acidity, leading to lower overall taste scores (see illustration below).

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Conclusion

To conclude, here's what was found in this research, answering the questions brought up above:

Extraction yield: A rippled tamper base does marginally increase extraction yield (+0.5 to +1.0 percentage points).

Flow mechanics & uniformity: The rippled base reduces overall puck resistance and accelerates initial wetting, but offers no discernible benefit to extraction uniformity.

Sensory quality & puck condition: Despite increasing extraction yield, the rippled base negatively impacts cup quality by increasing astringency and lowering acidity. Additionally, it yields slightly less crema and provides no measurable improvements to post-extraction puck compactness or dryness.

What spraying your puck does to coffee

Introduction

In an effort to better understand espresso extraction dynamics—particularly regarding top-puck water distribution and pre-infusion behavior—this experiment by Stéphane Ribes explores the impact of spraying water directly onto the surface of an already-tamped coffee puck prior to loading the portafilter. Inspired by discussions surrounding top paper filters, spacers, and shower screen distribution, this test evaluates how pre-wetting the top grinds influences puck resistance, flow mechanics, extraction yield, and final shot characteristics.

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Main questions asked

Does spraying water on a tamped coffee puck produce visible or measurable changes in espresso extraction behavior?

How does top-puck pre-wetting affect puck resistance, infusion pressure, and liquid flow profile?

Can coarsening the grind setting offset any increase in puck resistance without sacrificing Extraction Yield (EY)?

What sensory or visual differences (such as wetting speed, center flow, and blonding time) occur when the puck surface is pre-wetted?

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Methodology & proceeding

Equipment & Setup

Machine & screen: Decent Espresso DE1PRO v1.1 machine paired with an IMS SI200 shower screen (used to achieve drier pucks and consistent extraction dynamics).

Basket & dose: 14.5g coffee dose in a 15g VST basket targeting a 29g yield (1:2 ratio).

Grinder: Mahlkönig EK43.

Testing process

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Results

Significant Increase in Puck Resistance: Spraying just 1g of water on the tamped puck caused a surprising and marked rise in puck resistance. Increasing the spray to 2g intensified this effect even further.

Here's a comparison of what the chart looks like without water spray vs. 1g of water spray.

Grind Compensation & Pressure: To avoid excessively high extraction pressure with 2g of sprayed water, the grind size had to be coarsened significantly (from EK 1.4 to EK 1.6).

Here's a comparison of what the chart looks like at different grind sizes, namely EK1.4, EK1.5 and EK1.6.

Flow & wetting dynamics:

Pre-wetted pucks (especially with 2g of spray) consistently initiated extraction closer to the center of the basket.

The coarser grind setting allowed for faster puck wetting during infusion while maintaining peak extraction pressure comparable to finer, non-sprayed shots.

Visual "blonding" appeared to start noticeably later on pre-wetted shots.

Extraction Yield (EY): All tested configurations maintained virtually stable extraction yields between 19.4% and 19.7%. Notably, EY showed no degradation even when the grind was coarsened to offset the increased puck resistance.

Taste profile: No clear improvements in taste were detected during initial trials, though bean quality may have influenced sensory outcomes.

Here's a selection of videos of 4 of the tested configurations:

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Conclusion

In conclusion, we can answer the questions that were brought up as follows:

Does spraying water on a tamped coffee puck produce visible or measurable changes in espresso extraction behavior? Yes. Pre-wetting the top of a tamped puck with 1g to 2g of water creates immediate, measurable changes by significantly increasing puck resistance, modifying flow initiation patterns, and altering pre-infusion behavior.

How does top-puck pre-wetting affect puck resistance, infusion pressure, and liquid flow profile? Pre-wetting only the top layer (~5%) of the coffee bed creates a localized barrier that sharply increases puck resistance and peak infusion pressure. To maintain reasonable pressure levels, the grind setting must be coarsened.

Can coarsening the grind setting offset any increase in puck resistance without sacrificing Extraction Yield (EY)? Yes. Coarsening the grind size (e.g., moving from EK 1.4 to 1.6) successfully brings extraction pressures back to normal levels while maintaining a consistent Extraction Yield between 19.4% and 19.7%.

What sensory or visual differences (such as wetting speed, center flow, and blonding time) occur when the puck surface is pre-wetted? Visually, pre-wetted pucks cause the extraction to start closer to the center of the basket, delay the onset of visual blonding, and enable faster overall puck wetting when paired with a coarser grind setting. Sensory testing showed no clear improvement in taste under initial trial conditions.

Which puck preparation technique is best?

This article is based on an investigation into espresso puck preparation techniques conducted by Stéphane Ribes in June 2020 (v1.1). For reference, here's Stéphane's original PDF. Using a Decent Espresso machine (DE1PRO v1.1) and a blooming shot profile, the experiment evaluates the impact of various distribution methods, tapping, and deep-needle alignment tools (such as the Hog tool) on extraction dynamics, yield, and shot clarity/taste.

Questions

The following questions were investigated across the tests:

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Method

The tests were performed following a strict standard protocol to ensure test reliability:

Machine & basket: Decent Espresso DE1PRO v1.1, Cafelat 8.0 mm silicone gasket, IMS SI 200 IM shower screen, VST 22g ridgeless filter basket.

Grinder & beans: Mahlkönig EK43 S with SSP "High Uniformity" (Silver Knight coating) burrs, single-dosed and ground frozen (setting EK1.7).

Water & thermal control: Montille water re-mineralized to 40 ppm CaCO3 alkalinity and 90 ppm CaCO3 hardness; portafilter pre-heated to 80°C in a kettle; basket and screen wiped dry before every shot.

Dose & ratio: Standard dose of 18.5 g (unless specified otherwise) targeting a brew ratio of 1:2.2.

Tamping: The Force Tamper (58.5 mm smooth flat base) at 24 lbs spring pressure.

Brew profile: 20-second blooming profile with a slow ramp (15 sec) followed by 2.2 mL/s flow rate extraction.

Measurement: TDS measured with an unfiltered Atago PAL refractometer at room temperature after vigorous stirring (each data point represents an average of 3 to 5 measurements).

Proceeding The experimental runs were conducted over two main test dates:

June 13, 2020 Tests: Compared varied distribution methods including no distribution (nothing, portafilter circular motion, surface raking, full WDT with 0.7 mm needles (Londinium tool), full WDT with 0.4 mm home-made needles, WDT + gentle vertical taps, and WDT + vertical taps + Hog tool.

June 23, 2020 Tests: Evaluated consistency across fixed dose variations (18.5 g vs 19.0 g) comparing no distribution, WDT (0.4 mm) + taps, and WDT (0.4 mm) + taps + Hog tool.

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Results

The main findings and detailed metric comparisons from the tests are detailed below:

Main Findings:

Combining WDT through the full height of the puck using 0.4 mm needles with gentle vertical taps before tamping produced the best and most consistent results.

The Hog tool (95 spikes of 0.8 mm) applied after WDT + vertical taps yielded faster puck wetting, higher extraction resistance, and improved taste profiles (increased sweetness and fruity acidity).

Skipping distribution entirely occasionally produced high EY or tasty shots, but lacked consistency compared to WDT methods.

Visual extraction uniformity did not reliably correlate with higher EY values or superior taste scores.

Higher extraction yields consistently correlated with the highest-rated shots in taste tests.

Here's a table summarizing the tests and results:

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Conclusion

Based on the findings, we can answer our questions as follows:

Combining deep WDT throughout the entire height of the coffee bed using thin 0.4 mm needles with gentle vertical taps prior to tamping produces the highest consistency and overall shot quality.

Thinner needles (0.4 mm) perform better than thicker needles (0.7 mm Londinium tool), providing smoother distribution without creating macro-channels or excessive disruption in the bed.

The Hog tool significantly increases extraction resistance and speeds up initial puck wetting, leading to enhanced sweetness and fruity acidity alongside top-tier extraction yields (up to 22.7%).

Gentle vertical taps collapse deep air pockets and level the coffee bed, facilitating cleaner, more uniform flow dynamics and preventing premature channeling.

No, visual uniformity during extraction does not always correlate directly with higher EY or superior taste scores.

Lowering the dose slightly (e.g., from 18.5 g to 18.0 g) under fine grind settings speeds up initial flow ("first drop in cup") while preserving or enhancing peak pressure and total extraction yield.

Effects of a puck screen on extraction

The distribution of Extraction Yield (EY) across an espresso puck is rarely uniform. This study by Stéphane Ribes from April 2021 investigates radial uniformity during extraction and evaluates how placing a BPLUS contact screen (also called "puck screen") directly above the ground coffee puck alters both local extractions and the overall shot yield across VST and Pullman filter baskets.

Core research questions

This study aims to answer three key questions:

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Methodology & experimental setup

To isolate the variables influencing extraction uniformity, a precise, highly controlled testing framework was established.

Espresso machine: Decent Espresso Machine DE1PRO v1.1, featuring an S22A Ultem prototype shower and an IMS CI 200 IM shower screen (protruding 9.6 mm into the basket).

Grinder: Levercraft Ultra Grinder equipped with SSP High Uniformity blind burrs (Red Speed coating), run at 100 RPM at a grind setting of 2.0 (100 microns above the burr touch point).

Water specifications: Montcalm water sourced from the Pyrenees, France (4 ppm eq. CaCO3 alkalinity and 10 ppm eq. CaCO3 total hardness).

Extraction profile: Easy Blooming profile set to 90°C, featuring a 2.5 bar bloom exit pressure and a 7.5 bar maximum extraction pressure.

Dose & brew ratio: A fixed 19.0g coffee dose pulled to a 1:2.0 brew ratio across all test iterations.

Filter baskets: 20g VST basket and 20g Pullman basket.

Preparation & puck workflow:

Portafilter and filter basket were pre-heated to 80°C in a kettle prior to testing.

Basket and shower screen were thoroughly dried before every shot.

Single doses of frozen coffee beans were ground directly into the basket.

Distribution was performed using a Levercraft WDT tool (8 x 0.4mm needles), raked with a BPLUS stirrer, and finished with an SworksDesign PorcuPress v1 (109 x 0.8mm needles).

Ground coffee was tamped using a 58.5mm flat base Bravo Tamper at 26lbs of force, applying a light polishing step when no contact screen was used.

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Measurement & data logging procedure**

TDS testing: Total Dissolved Solids were measured using an Atago PAL refractometer zeroed with Montcalm water.

Sample handling: Unfiltered coffee samples were vigorously stirred and brought to room temperature before taking readings. Every reported data point reflects the average of 3 to 5 individual measurements.

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Results

The data obtained through the experiments demonstrates a significant improvement in extraction uniformity and overall efficiency when applying a BPLUS contact screen across both VST and Pullman filter baskets. Below are all the Extraction Yields (EY) found:

The data shows the following:

Edge underextraction without contact screen: Without the BPLUS screen, both filter baskets exhibit a sharp decline in extraction yield toward the outer edge of the puck (25% center vs. 16%-17% outside).

Uniformity gains with contact screen: Adding the BPLUS screen dramatically elevates outer edge extraction from 17% to 22% in the VST basket and from 16% to 23% in the Pullman basket, creating a far more even extraction profile across all radial zones.

Increase in total Extraction Yield: By mitigating severe periphery underextraction, the overall shot Extraction Yield increases by +2% in the VST basket (reaching 24%) and +3% in the Pullman basket (reaching 24%).

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Conclusion & key takeaways

Based on the findings, the questions can be answered as follows:

Standard espresso extractions exhibit significant radial non-uniformity. Without a contact screen, extraction at the outer perimeter of the puck (representing roughly 30% of the total dose weight) is severely underextracted, reaching only about two-thirds (approx 16%-17%) of the extraction yield measured at the center (approx 25%).

Placing a BPLUS contact screen directly above the coffee puck significantly improves radial uniformity. It lifts the outer extraction yield from 16%-17% up to 22%-23%, balancing extraction across the center, middle, and outer radial sections.

By eliminating severe underextraction at the outer edges of the puck, the BPLUS contact screen delivers a substantial increase in overall shot extraction yield for both basket types: increasing from 22% to 24% in the VST basket, and from 21% to 24% in the Pullman basket.

In conclusion, using a puck screen significantly improves radial uniformity.

Higher extraction flow rates without channeling?

1. Introduction

This article is based on research from Stéphane Ribes from February 2020. It investigates the adaptation of a hybrid "lever-blooming" profile on a Decent Espresso DE1PRO v1.1 machine. The core focus of this study is determining whether adjustments to profile steps allow for higher final extraction flow rates while maintaining the target extraction pressure range and mitigating puck channeling.

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2. Questions

The investigation focuses on answering the following key questions:

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3. Method

Equipment

Decent espresso machine: DE1PRO v1.1 equipped with a red Cafelat 8.0mm silicone gasket.

Shower screen: IMS SI 200 IM screen (used without a spacer).

Grinder: Mahlkönig EK43 S equipped with SSP "High Uniformity" burrs featuring a Silver Knight coating.

Filter basket: VST 15g ridgeless filter basket.

Tamper: The Force Tamper with a 58.35mm US curved smooth base, applied twice per shot.

Water & Coffee Preparation

Water: Montille water adjusted using sodium carbonate and Epsom salts to achieve 50ppm eq. CaCO3 alkalinity and 125 ppm eq. CaCO3 total hardness.

Preparation workflow: Frozen beans were single-dosed and ground into a double-walled stainless steel cup. The filter basket and shower screen were thoroughly dried prior to each shot. Basket Weiss Distribution Technique (WDT) was performed using a Londinium tool with a Decent funnel, followed by gentle raking with a Hog tool to create a uniform surface (ensuring no vertical tapping). Puck preparation was completed using a Hog tool mounted on a stand to ensure precise vertical motion.

Measurement protocol

Refractometer: Atago PAL refractometer zeroed with the adjusted Montille water.

Sampling: Unfiltered coffee samples were measured at room temperature after vigorous stirring.

Averaging: Each reported data point represents the average of 3 to 5 separate measurements.

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4. Proceeding

Tested profiles

Profile A (1.5mL/s extraction flow rate):

Recipe: 14g dose in, 34g yield out (Brew Ratio 1:2.4).

Variations: Compared a shorter pressurized bloom (4 s) paired with a longer flow ramp (12 s) against a longer bloom (12 s) paired with a shorter flow ramp (4 s).

Shot duration: Total shot times ranged between 40 s and 45 s.

Profile B (2.5mL/s extraction flow rate):

Recipe: 13g dose in, 31g yield out (Brew Ratio 1:2.4).

Variations: Compared a shorter bloom (4 s) paired with a longer flow ramp (10 s) against a longer bloom (10 s) paired with a shorter flow ramp (4 s).

Shot duration: Total shot times ranged between 29 s and 35 s.

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5. Results

The table below outlines the measured Extraction Yield (EY) data collected across various grind size settings on the Mahlkönig EK43 S:

At 2.5mL/s, the experiments resulted in an identical Extraction Yield (EY) range of 19.4% – 19.9% for both bloom/flow rise variations. At 1.5mL/s, the 12s Bloom / 4s Flow Rise setup achieved an EY range of 19.4% – 19.7%, while the 4s Bloom / 12s Flow Rise setup yielded slightly higher at 19.5% – 20.1%.

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6. Conclusion

The following can be concluded from the experiments:

Yes. Higher flow rates (2.5mL/s) are achievable without channeling by making specific profile adaptations. Coarser grind sizes are used to maintain target pressure ranges, requiring a lower pressure limit during the pressurized bloom step to prevent premature drippage.

A gentler, slower increase in flow rate (Step 3 transition) helps avoid sour shots by mitigating puck channeling. Extraction Yields remain highly consistent (19.4% - 20.1%) across various grind size adjustments.

At 2.5 mL/s, the profile requires coarser grind settings and a lower pressure limit during the pressurized bloom step to prevent premature drippage. Despite completing much faster (29–35 s compared to 40–45 s for the 1.5mL/s profile), the 2.5mL/s profile achieves virtually identical extraction yields (19.4%–19.9% vs. 19.4%–20.1%). Both flow rates successfully eliminate puck channeling and avoid sour shots as long as a gentle flow transition step is applied.

The impact of the preinfusion flow rate on espresso extraction

1. Introduction

This research by Stéphane Ribes (April 2020) evaluates the physical and chemical impacts of pre-infusion flow rates on espresso extraction dynamics using a light-medium espresso roast. By leveraging the Decent Espresso platform, the study examines how varying initial water flow rates during pre-infusion alter peak extraction pressure, espresso yield, total dissolved solids (TDS), and extraction yield (EY) while holding other variables like grind size and temperature constant.

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2. Questions

How does altering the pre-infusion flow rate affect the peak pressure and extraction velocity when keeping the dose, grind size, and target yield constant?

How does pre-infusion flow rate impact the extraction yield (EY) of an espresso roast?

How must coffee dose weight be adapted across different pre-infusion flow rates to maintain a consistent peak extraction pressure (~6 bar)?

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3. Method

Machine & setup: Decent Espresso DE1PRO v1.1 machine with a Cafelat 8.0mm silicone gasket and IMS SI 200 IM shower screen (no spacer).

Grinder & preparation: Mahlkönig EK43 S grinder with SSP "High Uniformity" burrs. Puck preparation utilized a double-walled stainless steel cup, a Londinium WDT tool with Decent funnel, a Hog puck preparation tool on a vertical stand, and The Force Tamper with a 58.5mm smooth flat base (applied twice).

Water & thermal protocol: Portafilter pre-heated to 70°C in a kettle; basket and screen dried completely prior to each shot. Remineralized Montille water (50ppm CaCO3 alkalinity, 125ppm CaCO3 hardness). Extraction performed using a hybrid "Lever-Blooming" profile at 85°C with a target main extraction flow rate of 2.5mL/s.

Coffee & ratio: Colombia Huila Tesoro Gigante (Natural, Espresso Roast by OR Roastery). VST 15g ridgeless basket with a 13g dose aiming for a 30g output (brew ratio of 2.3) over a 33-second total shot time.

Measurement: Atago PAL refractometer zeroed with adjusted water; all samples measured at room temperature without filtering, taking the average of 3 to 5 readings per sample.

Below are the parameters used for the Hybrid "Lever" Blooming profile:

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4. Proceeding

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5. Results

Here's the results found via the experiments, first with a constant 13g dose and then adjusting the dose upwards or downwards:

The following table shows all the results of the experiments in one view:

Said results reveal key insights into how pre-infusion flow rates shape extraction hydraulics and puck dynamics:

Non-linear peak pressure behavior (fixed 13.0g dose): Peak extraction pressure follows a non-linear, U-shaped relationship as pre-infusion flow rate increases. At low rates (2.4\mL/s), the pressure peaks at about 6.4 bar. Mid-range rates (3.0–4.0mL/s) drop to lower peak pressures (about 4.6–4.8 bar) due to reduced early bed compaction. High flow rates (6.0–8.0mL/s) violently fill and compact the puck early, driving peak extraction pressures sharply up to about 8.7–8.8 bar.

Inverted dose adjustment for pressure normalization (6 bar target): To maintain a uniform 6 bar peak pressure, dose weight must inversely compensate for puck compression. Mid-range flow rates (3.0–4.0mL/s) require adding coffee (+0.3g, total 13.3g) to raise bed resistance to about 6.2 bar. High flow rates (6.0–8.0mL/s) require subtracting coffee (-0.3g, total 12.7g) to reduce resistance and bring peak pressure down to about 6.0 bar.

Extraction Yield (EY) invariance: Across all profiles—whether fixed-dose or dose-adapted—Extraction Yield remains virtually static between 19.5% and 20.0%. This confirms that pre-infusion flow rate acts primarily as a physical lever for hydraulic pressure and flow dynamic control rather than a chemical solvent driver.

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6. Conclusion

The experimental findings demonstrate how pre-infusion flow rates modulate coffee bed resistance and puck compression, establishing the necessary dose compensations to maintain target extraction pressures.

How does altering the pre-infusion flow rate affect peak extraction pressure when maintaining constant grind size, coffee dose (13g), and shot duration (33s)?

Mid-range pre-infusion flow rates (3.0–4.0mL/s) produce the lowest peak extraction pressures (about 4.6–4.8 bar) due to lower initial bed compression. Fast pre-infusion flow rates (6.0–8.0mL/s) forcefully fill and compress the coffee puck early, causing peak pressures to surge to about 8.7–8.8 bar.

How does pre-infusion flow rate impact the overall Extraction Yield (EY) of an espresso roast?

Pre-infusion flow rate has virtually no effect on Extraction Yield. Across all testing conditions—both unadjusted and dose-adjusted—EY remains locked within a tight band of 19.5% to 20.0%.

How must coffee dose weight be adapted across different pre-infusion flow rates to normalize the extraction to a constant peak pressure (~6 bar)?

For moderate pre-infusion flow rates (3.0–4.0\mL/s), the dose must be increased by +0.3g (13.3g) to build sufficient bed resistance. For rapid pre-infusion flow rates (6.0–8.0mL/s), the dose must be decreased by -0.3g (12.7g) to reduce resistance and prevent high peak pressures.

Easy Blooming: What ending preinfusion at a target pressure (dynamic bloom) and a pressure decline during extraction do to coffee

1. Introduction

This article is based on Stéphane Ribes' September 2020 Easy Blooming study, conducted on the Decent Espresso DE1PRO v1.1. The work investigates whether the conventional blooming-espresso approach can be made more tolerant of changes in grind size by replacing a bloom of predetermined duration with a dynamic bloom stage that ends when puck pressure reaches a defined threshold.

In a conventional blooming profile, the bloom lasts for a fixed period regardless of the hydraulic resistance of the coffee puck. If the grind is changed, however, water penetration and pressure development also change. Ribes therefore tested a pressure-triggered alternative: instead of ending the bloom after a fixed number of seconds, the machine advances to the next stage when measured pressure reaches a specified value.

The underlying hypothesis is that the bloom duration should adapt automatically to puck resistance. A coarser grind, which offers less resistance, should reach the pressure threshold sooner and therefore receive a shorter bloom. A finer grind should reach the threshold later and consequently receive a longer bloom.

The presentation states that this behavior makes extraction pressure less sensitive to grind variation and that espresso prepared at the most extreme grind settings was more enjoyable when the dynamic bloom was used.

The study then extends the concept further by combining dynamic blooming with pressure-priority extraction and a dynamic pressure decline. In this configuration, the rate of pressure decline changes according to the evolution of water flow, with the intention of stabilizing flow during the latter part of the extraction.

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2. Questions asked

The experiments address six principal questions:

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3. Method

Equipment and preparation protocol

The general test protocol used a Decent Espresso DE1PRO v1.1, a Mahlkönig EK43 S grinder fitted with SSP High Uniformity burrs with Silver Knight coating, and Montcalm water adjusted to 35 ppm CaCO₃-equivalent alkalinity and 112 ppm CaCO₃-equivalent total hardness using sodium carbonate and Epsom salts.

The portafilter and basket were preheated to 80°C in a kettle. Before every extraction, the basket and shower screen were dried completely with a clean tissue. Frozen beans were single-dosed and ground into a double-walled stainless-steel cup.

Puck preparation consisted of WDT in the basket using a homemade tool with three 0.4 mm needles and a Decent funnel, followed by gentle vertical taps. A Bravo Tamper, 58.50 mm in diameter, set to 36 lb, was used for tamping. For the tests performed on 19 September, a Hog puck-preparation tool with 0.8 mm needles was inserted and withdrawn vertically using a stand to ensure straight movement.

TDS measurements were performed with an Atago PAL refractometer, zeroed with the adjusted Montcalm water. Samples were not filtered and were measured at room temperature after vigorous stirring. Each reported data point represents the mean of three to five measurements.

Experiment 1: fast flow rise

The first experiment was conducted on 12 September 2020 using naturally processed Guatemalan coffee. The recipe was:

18 g dose

18 g VST basket

45 g beverage output

Decent mesh shower screen

no Hog tool

grind settings from EK1.9 to EK1.4

The profile used is called Easy Blooming. In the first round of the experiment, a 30-second fixed bloom was used followed by a 5-second ramp to 2.2 mL/s. In the second round of the experiment, the bloom ended when pressure reached 1.5 bar (dynamic bloom), followed by the same 5-second ramp to 2.2 mL/s.

Experiment 2: slow flow rise

The second test used the same coffee, dose, basket, output, shower screen, and grind range, but extended the post-bloom ramp to 12 seconds (vs. the 5 seconds in experiment 1).

The presentation contains one labeling inconsistency that should not be silently resolved: page 8 identifies the fixed comparator as a 20-second bloom, while page 9 identifies it as a 30-second bloom. Both slides specify a 12-second flow ramp to 2.2 mL/s. As in experiment 1, the first round of the experiment with a fixed bloom was followed by a dynamic bloom, which ended when pressure reached 1.2 bar.

Experiment 3: pressure-priority extraction with dynamic decline

A separate experiment was conducted on 19 September 2020 with anaerobically fermented Costa Rican coffee:

19 g dose

22 g VST basket

53 g output

IMS SI200 IM shower screen

thin Hog tool

grind settings from EK2.1 to EK1.6

Both profiles used a dynamic bloom ending at 1.5 bar. The flow-priority comparator then used a 5-second ramp to 2.2 mL/s, whereas the alternative moved into a 6-bar pressure-priority extraction with dynamic pressure decline.

The presentation illustrates dynamic decline rates of approximately −0.2 bar/s, −0.1 bar/s, and −0.04 bar/s. A faster increase in water flow results in a steeper pressure decline.

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4. Proceeding

For the flow-priority experiments, each profile was repeated across a sequence of six EK43 grind settings. The fixed-bloom profile was used as the reference, while the dynamic version replaced the time-based bloom termination with a pressure threshold.

The effect of the profile was then evaluated through:

total shot time;

extraction pressure peak;

beverage mass that dripped from the puck before the main extraction stage (called drippage);

extraction yield;

visual cup appearance;

taste score;

mouthfeel;

sweetness;

acidity;

flavor clarity;

bitterness; and

astringency.

The essential adaptive behavior can already be seen in the summary slide. With the same pressure-triggered bloom, the coarse EK1.9 grind receives an approximately 20-second bloom, whereas the fine EK1.4 grind receives an approximately 40-second bloom. A fixed-duration profile gives both grinds the same 30-second bloom.

The pressure-priority experiment subsequently examined whether dynamic blooming could be combined with an extraction whose pressure declines in response to flow behavior. The purpose was not simply to reduce pressure, but to make late-shot flow more uniform across grind settings.

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5. Results

5.1. Fast flow rise

The fast-ramp experiment shows a clear difference in how shot duration responds to grind resistance. With the fixed bloom, total shot time remains relatively stable at roughly 57–60 seconds across most of the grind range. With dynamic blooming, coarse-grind shots become much shorter—approximately 46–47 seconds at EK1.9–EK1.8—while fine-grind shots become substantially longer, reaching roughly 68 seconds at EK1.5 and 73 seconds at EK1.4.

This is expected from the control logic: coarse pucks reach the 1.5-bar trigger rapidly, whereas finer pucks remain in the bloom stage for longer.

Extraction yield

Extraction yield remains comparatively insensitive to the bloom strategy. Both profiles cover roughly 22–25% EY, with the highest values at the coarser end and progressively lower yields toward EK1.4.

Approximate values from the graph are:

Thus, dynamic blooming does not materially increase EY across the entire range, although it appears to preserve slightly more extraction at the fine end.

Drippage before extraction

At coarse settings, dynamic blooming markedly reduces the beverage mass released before the main extraction stage. At EK1.9, the fixed bloom produces roughly 7.5–7.7 g of early drippage compared with approximately 5.8 g under dynamic bloom.

The relationship reverses toward the fine end. At EK1.4, the fixed profile produces less than approximately 1 g, whereas the dynamic profile produces around 3 g. Dynamic blooming therefore redistributes bloom duration according to puck resistance rather than minimizing drippage uniformly.

Extraction pressure

The largest pressure peaks occur at the fine end of the grind range. Around EK1.5–EK1.4, peak extraction pressure approaches approximately 12–13 bar under the fixed profile. Dynamic bloom lowers these extreme peaks modestly, to approximately 11–12 bar.

The difference is relatively small in the middle and coarse parts of the range, but it supports the presentation's central claim that extraction pressure becomes somewhat less sensitive to grind variation.

Sensory results with fast flow rise

The sensory graphs show the clearest advantage of dynamic blooming not at the optimum grind, but toward the edges of the grind range.

Both profiles produce their highest taste score around EK1.7, at approximately 8/10. At that grind, the two profiles are essentially equivalent.

At more extreme settings, however, the dynamic profile performs better:

EK1.8: approximately 6 versus 4;

EK1.5: approximately 6 versus 4;

EK1.4: approximately 3 versus 2.

Dynamic blooming also keeps sweetness relatively stable at approximately 3/5 across the range, whereas the reference profile falls to about 2/5 at several settings. Flavor clarity is likewise more stable, particularly around EK1.5. Astringency remains broadly comparable and does not show an obvious penalty from dynamic blooming.

Here's the taste scores of the coffee. As stated before, in our context, "Quick flow rise" is the fixed bloom shots, whereas "Easy quick" is the dynamic bloom shots:

The cup photographs are consistent with the quantitative results in showing usable espresso throughout the tested range, but the study's principal distinction is sensory rather than simply visual.

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5.2. Slow flow rise

The slower 12-second ramp produces the same general adaptive behavior but with somewhat different hydraulic effects.

With a fixed bloom duration, total shot time of Easy Blooming is approximately 50–53 seconds across all grind sizes. With dynamic bloom (namely moving on once pressure reaches 1.5 bar) shot times vary much more widely: roughly 39–40 seconds at EK1.9–EK1.8, approximately 44–49 seconds in the middle, and approximately 56–61 seconds at EK1.5–EK1.4.

Extraction yield

Again, EY changes little between the two strategies.

Approximate values are:

The two profiles therefore produce broadly similar extraction yields despite substantially different bloom durations.

Drippage before extraction

Dynamic bloom has a large effect at coarse settings:

EK1.9 fixed: approximately 7 g

EK1.9 dynamic: approximately 3 g

By EK1.7, the values converge near 2 g. At finer settings, the fixed bloom approaches virtually zero drippage, whereas the dynamic profile retains roughly 1 g.

Pressure peak

Peak pressure rises sharply as the grind becomes finer.

At approximately EK1.5, the shot with fixed bloom reaches nearly 12 bar, while the dynamic bloom shot is closer to 10 bar. At EK1.4, both remain very high, but the dynamic bloom shot is still approximately one bar lower.

Thus, the pressure-triggered bloom again moderates, rather than eliminates, the increase in peak pressure caused by a much finer grind.

Sensory results with slow flow rise

The sensory data again indicate that dynamic blooming is most useful at the boundaries of the grind range.

The approximate overall taste scores are:

The improvement at EK1.4 is particularly notable. The fixed-bloom shot receives a very low score, while the dynamic version remains substantially more acceptable.

Dynamic bloom also preserves flavor clarity at the finest grind. The reference profile falls from approximately 3/5 to 1/5 at EK1.4, whereas the dynamic profile remains near 3/5. Bitterness at the fine extreme is also slightly lower, approximately 3/5 rather than 4/5. Sweetness and mouthfeel are generally equal or slightly better with dynamic bloom.

Here's all the results from the sensory analysis:

These results directly support Ribes' summary that the most extreme grind settings were more enjoyable when the bloom duration was pressure-triggered rather than fixed.

As in the previous experiment, the coffees looked fine from a visual perspective. However, what really matters when drinking coffee is that it tastes well:

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5.3. Pressure-priority extraction with dynamic pressure decline

The final experiment extends the concept from bloom control into the extraction itself.

Both profiles begin with a bloom ending at 1.5 bar. In the first round of experiments, flow then ramps up to 2.2 mL/s over five seconds and is held constant. The alternative enters a 6-bar pressure-priority phase whose pressure declines dynamically.

Extraction yield is very similar between the two methods, remaining approximately 22.5–23.5% throughout the EK2.1–EK1.6 range.

There is no consistent EY advantage for either strategy.

Sensory consistency, however, improves with pressure decline.

Approximate taste scores are:

Here's all the results from the sensory analysis. The "Easy quick flow" stands for the shots with fixed flow and the "pressure decline" speaks for itself:

The conventional flow-priority version reaches a slightly higher peak score at EK1.9, but its performance deteriorates rapidly toward the finest grind. In contrast, the dynamic-decline profile remains relatively stable.

The same pattern appears in other sensory variables. Mouthfeel with dynamic pressure decline remains near 2–3/5 rather than dropping to approximately 1/5 at coarse settings. Flavor clarity remains close to 3/5 throughout the entire range, whereas the flow-priority profile rises to approximately 4/5 around EK1.8 before collapsing toward roughly 1/5 at EK1.6. Bitterness and astringency remain restrained.

The presentation therefore concludes that combining dynamic bloom with pressure-priority extraction further widens the usable grind range and that dynamically increasing the pressure-decline rate as flow rises produces more consistent flow late in the extraction.

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6. Conclusion

Taken together, the experiments indicate that “Easy Blooming” is primarily a robustness strategy rather than a mechanism for substantially increasing extraction yield. A pressure-triggered bloom allows the profile to adapt its duration to puck resistance, reducing sensitivity to grind-size variation and improving sensory performance when the grind is considerably coarser or finer than the apparent optimum. The subsequent addition of dynamic pressure decline extends that principle into the extraction phase and improves consistency across an even broader grind range.

1. Can a pressure-triggered dynamic bloom make extraction less sensitive to grind size than a fixed-duration bloom?

Yes. With dynamic blooming, the bloom terminates according to puck pressure rather than elapsed time. Coarse grinds reach the pressure threshold sooner, while fine grinds remain in bloom longer. This makes extraction pressure less influenced by grind variation.

2. How does dynamic blooming affect bloom duration, shot time, drippage, pressure, extraction yield, and sensory quality?

It changes the hydraulic behavior substantially but affects EY only modestly. Bloom and total shot duration become adaptive: coarse-grind shots shorten and fine-grind shots lengthen. Dynamic blooming reduces early drippage at coarse settings and moderately suppresses the very high pressure peaks observed at the finest settings. Extraction yield remains close to that of the fixed-bloom profiles, while sensory results improve at several off-center grind settings.

3. Does dynamic blooming improve espresso at the coarse and fine extremes?

Yes. This is one of the strongest findings. Both fast- and slow-ramp experiments show markedly better taste scores at some extreme grind settings. Shots at the most extreme settings were more enjoyable with dynamic bloom.

4. How does the behavior differ between fast and slow post-bloom flow rises?

Both benefit from dynamic blooming, but the slower ramp appears especially tolerant at the finest end. The fast-ramp profile improves several coarse and fine settings while preserving a strong optimum around EK1.7. The slow-ramp version produces particularly large improvements at EK1.4, including substantially better taste score and flavor clarity.

5. Can pressure-priority extraction with dynamic pressure decline further widen the usable grind range?

Yes. The pressure-decline profile produces a more even sensory response from EK2.1 through EK1.6 than dynamic bloom followed by flow-priority extraction alone. Although extraction yield remains similar, taste scores and flavor clarity are substantially more consistent. Ribes explicitly identifies this as a further widening of the range of grind settings that yield enjoyable espresso.

6. Does dynamic pressure decline make the final extraction flow more consistent?

Yes. The decline is designed to become steeper when water flow rises more rapidly—illustrated with decline rates of approximately −0.04, −0.1, and −0.2 bar/s. This produces a more consistent flow rate during the final part of the extraction.

Easy Blooming, compared to the Default and Gentle & Sweet profiles

Introduction

This experiment by Stéphane Ribes (October 2020) evaluates the performance of the "Easy Blooming" espresso pressure profile in comparison to two standard Decent Espresso profiles: "Default" and "Gentle & Sweet". The study investigates how extraction dynamics across various grind sizes influence sensory attributes and overall extraction yield. Here's the slides of this presentation.

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2. Questions asked

Question 1: How does the "Easy Blooming" profile compare to "Default" and "Gentle & Sweet" in terms of overall taste score, flavor clarity, and extraction yield across different grind settings?

Question 2: Does "Easy Blooming" effectively reduce standard extraction defects—such as excessive bitterness and astringency—when grinding finer?

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3. Method

Hardware: Decent DE1PRO v1.1 with S9 Ultem prototype screen and mesh shower screen.

Grinder & prep: Mahlkönig EK43 S (SSP High Uniformity burrs), Craig Lyn Shaker Funnel, WDT (0.4 mm needles), Hog puck tool (0.8 mm needles in stand), and Bravo Tamper (58.50 mm at 37 lbs).

Recipe parameters: 16.5 g dose of washed Colombian filter roast in an 18 g VST basket yielding 43 g output at 90 °C.

Water & TDS testing: Custom Montcalm water (35 ppm alkalinity, 112 ppm hardness). TDS measured via Atago PAL refractometer at room temperature (3–5 shot average per data point).

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4. Proceeding

Prepared single doses of frozen beans ground across six settings from coarse to fine (EK2.0 down to EK1.0).

Applied rigorous puck distribution using both fine WDT and vertical-stroke Hog puck preparation.

Extracted shots sequentially across the three profiles ("Easy Blooming", "Default", "Gentle & Sweet") at every grind step.

Measured total dissolved solids and evaluated sensory indicators including taste score, mouthfeel, acidity, bitterness, sweetness, clarity, and astringency.

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5. Results

Below are the resulting charts showing the results of the experiments:

The Default profile's highest taste score occurs around EK1.4, at approximately 6/10. Extraction yield rises toward the fine end, eventually reaching about 23.1% at EK1.0, but taste score declines sharply there.

Acidity is strongest at the coarse settings and falls continuously as the grind becomes finer. Mouthfeel follows a similar downward tendency.

In contrast, Gentle & Sweet produces comparatively stable acidity, mostly around 2–2.5, and extraction yield rises gradually as the grind becomes finer.

Its overall taste score improves from the coarse end but levels off at roughly 4.5/10 from EK1.4 onward. It never reaches the highest overall taste scores recorded by Default or Easy Blooming.

The winner among the profiles is Easy Blooming. It reaches approximately 23.4% at EK1.4, the highest plotted extraction yield in the experiment. Its taste score rises progressively from approximately 4 at EK2.0 to a maximum of approximately 7 at EK1.2. Clarity also peaks at 4 at EK1.2, higher than either comparison profile. Sweetness reaches about 3 from EK1.6 onward. Astringency decreases toward the finer settings and reaches its minimum, approximately 1.5, at EK1.2. The finest tested setting, EK1.0, does not continue improving the cup.

Although extraction yield remains high, taste score drops from about 7 to 5.5, mouthfeel falls to about 1, and clarity falls from about 4 to 3.

Below is a chart of the best scores of each profile, showing Easy Blooming outdoing the other profiles:

To summarize, the following overall best scores were achieved:

Extraction yield: Easy Blooming achieved the highest extraction yields, reaching about 23.4% at fine grind settings (EK1.4–EK1.0).

Taste score & clarity: Easy Blooming produced the highest overall taste scores (peaking around 7/10 at EK1.2) and led consistently in flavor clarity.

Off-flavor control: Astringency and bitterness remained controlled on Easy Blooming at finer grind settings, whereas Default experienced elevated astringency and sharp drops in acidity.

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6. Conclusion

Based on the sensory data and extraction trends captured across the profile test runs, the evaluated research questions yield the following findings:

How does the "Easy Blooming" profile compare to "Default" and "Gentle & Sweet" in terms of overall taste score, flavor clarity, and extraction yield across different grind settings?

Easy Blooming outperforms both alternative profiles by achieving higher extraction yields, superior flavor clarity, and noticeably higher taste scores, particularly at finer grind sizes (EK1.4 to EK1.2).

Does "Easy Blooming" effectively reduce standard extraction defects—such as excessive bitterness and astringency—when grinding finer?

Yes, Easy Blooming limits astringency and stabilizes bitterness even as grind size decreases, allowing high extractions without harsh, astringent off-notes.

Evaluating what Michael's spacer and various shower screens do to coffee

1. Introduction

In November 2019, Stéphane Ribes conducted several experiments to evaluate the impact Michael's 3.8mm brass spacer has on coffee made with a DE1PRO v1.1 espresso machine from Decent Espresso. A spacer is a device installed between the group-head shower and the water-diffusion screen, usually used to reduce head space (the distance between the upper surface of the puck and the shower screen).

The study, which can be downloaded here, examined whether changing the position of the shower screen—and therefore reducing head space—would influence pressure behavior, extraction uniformity, extraction yield, and sensory performance.

The spacer was not tested in isolation. Instead, Ribes compared four shower-screen configurations representing different degrees of protrusion into the basket and different puck-to-screen distances.

The four configurations were as follows:

All configurations were tested with a 15 g dose. The IMS CI 35 WM plus spacer created the greatest intrusion into the basket and therefore the most restricted headspace.

The central hypothesis is that reducing the puck-to-screen distance (aka headspace) might change the hydraulic behavior above the puck, produce a gentler pressure decline following peak pressure, and potentially improve extraction uniformity and cup quality.

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2. Questions asked

The following questions can be inferred from Stéphane's presentation:

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3. Method

The tests were carried out on a Decent Espresso Machine DE1PRO v1.1 fitted with a red Cafelat 8.0 mm silicone gasket.

A 15 g VST basket was used, each time with a 15 g dose.

Coffee was ground with a Mahlkönig EK43 S fitted with SSP “High Uniformity” burrs with Silver Knight coating.

The coffee used was Finca Los Cotuzos, a naturally processed bean from El Salvador, which was roasted on 30 October 2019.

The experiment used Montille water from Le Mont-Dore, France, adjusted to 50 ppm as CaCO₃ alkalinity and 100 ppm as CaCO₃ total hardness. The mineral composition was adjusted using sodium carbonate and Epsom salts.

Before every shot, both the basket and shower screen were thoroughly dried with a clean tissue.

The beans were ground into a double-wall stainless-steel cup. Distribution consisted of WDT in the basket with a Londinium tool and a Decent funnel, with no tapping afterward.

Tamping was performed using The Force Tamper with a 58.5 mm flat base, applied twice consecutively.

The profile was described as a mixture of a Londinium profile and a blooming shot. Its low-pressure bloom was specifically intended to maintain a relatively constant air-pocket volume above the puck and thereby limit additional damage to the puck surface when water flow subsequently increased.

Here's what the four programmed stages look like:

Thus, the profile intentionally separates rapid initial wetting from a pressure-controlled bloom and then raises flow progressively before maintaining a fixed flow.

TDS was then measured with an Atago PAL refractometer zeroed with SCAA water. Coffee samples were not additionally filtered. Samples were measured at room temperature after thorough agitation.

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4. Proceeding

The four configurations of shower screens and spacers tested were as follows:

The IMS CI 200 IM screen used was the standard screen included with the Decent Espresso machine. So it being tested without the spacer provided the baseline. The latter three configurations progressively moved the shower screen toward the puck, with the CI 35 WM plus spacer creating the smallest available head space.

Coffee was brewed in all configurations and the resulting espresso, basket/puck surface, shower screen, and knocked-out puck were documented.

First pressure comparison: similar maximum pressure

In the first round of experiments, the dose, extraction parameters, and workflow were held constant at 15 g. When the IMS CI 200 IM screen was used with the spacer, the grinder was tightened slightly, from EK1.3 to EK1.25, so that a similar maximum extraction pressure could be reached.

The primary measurement was the percentage pressure decline following the maximum pressure peak.

Second pressure comparison: identical grind setting

In the second round of experiments, the grinder was fixed at EK1.4, while maintaining the same extraction parameters and workflow.

The exception was the IMS CI 35 WM screen plus spacer. Because this arrangement placed the shower screen especially close to the puck, the dose had to be reduced from 15.0 g to 14.5 g to prevent direct puck-to-screen contact.

Pressure-level comparison

For each of the configurations, shots were brewed and compared at:

6–7 bar

9–10 bar

The following sensory and visual comparisons were then made:

visual extraction uniformity from the bottomless portafilter;

visual uniformity of the spent puck;

extraction yield;

body;

acidity;

sweetness;

flavor intensity;

bitterness;

astringency;

overall taste score.

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Results

5.1. Pressure decline after peak pressure

The first round of experiments found that with either the spacer or the IMS SI 200 IM screen installed, the pressure decline after maximum pressure was gentler.

The first comparison, in which maximum pressure was approximately matched, produced the following results:

The standard CI 200 IM arrangement therefore produced the steepest decline, losing roughly half of its peak pressure. Adding the spacer reduced that decline by approximately six percentage points.

The IMS SI 200 IM without a spacer behaved similarly to the CI 200 IM plus spacer, supporting the idea that screen position and head space—not merely the presence of a brass component—were responsible for much of the change.

The most extreme geometry, CI 35 WM plus spacer, produced by far the gentlest decline at approximately −30%, although its extraction yield in this test was also the lowest at 18.5%.

5.2. Same-grind comparison at EK1.4

At an identical EK1.4 grind setting, the same pattern appeared:

Again, the standard CI 200 IM produced the greatest pressure loss. The brass-spacer version and protruding IMS SI 200 IM screen both moderated the pressure decline substantially, while the CI 35 WM plus spacer once again produced the smallest drop.

Ribes thus noted again that less headspace, be it through a spacer or a shower screen, lead to a gentler pressure decline.

5.3. Experiments comparing the configurations at 6-7 bar vs 9-10 bar

Extraction yield at 6–7 and 9–10 bar

The combined extraction-yield chart gives the following values:

The results therefore do not show a general extraction-yield increase from adding the spacer. The conventional CI 200 IM arrangement actually produced the highest measured EY, approximately 19.5%, in the high-pressure condition.

The spacer's clearest benefit was instead in pressure behavior and visual extraction characteristics.

The CI 35 WM plus spacer is particularly revealing: despite producing the gentlest pressure decline, its extraction yield did not increase and actually fell to approximately 18.5% at 9–10 bar.

Visual extraction uniformity

Ribes separates visual uniformity into observations from the bottomless portafilter and the spent puck. Here's the charts showing his assessments:

And here's what the spent pucks looked like:

The standard IMS CI 200 IM configuration showed reasonable visual uniformity from the bottomless portafilter—particularly at 6–7 bar—but very poor visual puck uniformity at both pressure levels.

Adding the spacer to the CI 200 IM changed this markedly. Both the bottomless-portafilter assessment and the puck assessment moved toward the high-uniformity end of the graphical scales, and the 6–7 and 9–10 bar results were relatively close together.

The IMS SI 200 IM configuration also displayed comparatively high puck uniformity, although bottomless-portafilter uniformity was better at 6–7 bar than at 9–10 bar.

The CI 35 WM plus spacer behaved similarly: puck uniformity appeared strong at both pressures, while the bottomless-portafilter assessment was better at 6–7 bar than at 9–10 bar.

Taken together, these visual assessments support the hypothesis that reducing the distance between the screen and puck can improve the apparent uniformity and structural condition of the puck, even when extraction yield itself does not rise.

Taste assessment and taste scoring

Ribes then went ahead and evaluated the coffees made with each shower screen and spacer configuration for their body, acidity, sweetness, flavor, bitterness, astringency, and he also gave them an overall taste score. Here's the results:

Sensory results: standard IMS CI 200 IM

With the standard screen and no spacer, the sensory plot shows clear pressure-dependent differences.

At approximately 6–7 bar, the cup retained more acidity and flavor and exhibited somewhat less bitterness.

At 9–10 bar, the profile showed:

more body;

much lower acidity;

similar sweetness;

lower flavor intensity;

substantially more bitterness;

somewhat more astringency.

The overall taste score appears to be only about 2–3/10, with the lower-pressure version scoring slightly better than the higher-pressure shot.

Thus, the baseline screen configuration performed relatively poorly sensorially in this test.

Sensory results: IMS CI 200 IM plus spacer

Adding the brass spacer produced a substantially more balanced sensory pattern.

The differences between the 6–7 and 9–10 bar shots became comparatively small:

body remained moderate;

acidity remained moderate;

sweetness was low to moderate;

flavor was moderate;

bitterness remained low;

astringency was particularly low at 6–7 bar.

The total taste scores rise to approximately 4–4.5/10, noticeably above the unmodified CI 200 IM configuration.

This suggests that even though extraction yield was slightly reduced, cup balance improved.

Sensory results: IMS SI 200 IM

The protruding IMS SI 200 IM screen produced one of the strongest sensory outcomes in the experiment.

Its cups showed:

relatively high acidity;

relatively high sweetness, especially at 6–7 bar;

moderate flavor intensity;

extremely low bitterness;

extremely low astringency.

The overall taste score is approximately 5–5.5/10, substantially higher than the standard CI 200 IM and slightly higher than the CI 200 IM with spacer.

This reinforces the idea that the observed improvements were connected to screen geometry and reduced headspace, rather than being unique to the brass spacer itself.

Sensory results: IMS CI 35 WM plus spacer

The CI 35 WM plus spacer produced the greatest reduction in puck-to-screen distance and also yielded the highest plotted overall taste score.

At 6–7 bar, the cup shows approximately:

low-to-moderate body;

high acidity;

high sweetness;

relatively low flavor intensity;

almost no bitterness;

almost no astringency.

Its taste score is approximately 6/10, the highest individual result shown on the page.

At 9–10 bar, however, acidity and sweetness drop, while the overall taste score falls to approximately 4–4.5/10.

The configuration therefore appears to work particularly well at the lower 6–7 bar pressure range, rather than benefiting from a higher peak extraction pressure.

5.4. Overall comparison of all four shower screen and spacer configurations

The results reveal several important distinctions:

The experiment therefore separates two concepts that are often treated as equivalent: higher extraction yield and better extraction quality were not the same thing here.

The standard shower screen without space (baseline) generated the highest measured extraction yield, yet it showed the steepest post-peak pressure decline, the weakest puck-uniformity assessment, and the poorest taste results.

Conversely, configurations that reduced headspace produced smoother pressure behavior and generally better sensory scores even when their extraction yields were slightly lower.

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6. Conclusion

Taken as a whole, Ribes's experiments suggest that reducing headspace can materially change the hydraulic and sensory behavior of a Decent espresso extraction, but the benefits are expressed more clearly in pressure stability, puck uniformity, and cup quality than in extraction yield alone.

Based on the results, we can now answer the questions brought up in chapter 2 as follows:

1: Does installing the 3.8 mm brass spacer—or using a shower screen that similarly reduces headspace—change the pressure decline after the maximum extraction-pressure peak?

Yes. This is the clearest result of the experiment. With the standard IMS CI 200 IM screen, pressure declined by roughly 44–51% following the peak. Adding the spacer reduced this to approximately 37–45%. The protruding IMS SI 200 IM produced a similar improvement without a spacer, with declines around 36–45%, while the IMS CI 35 WM plus spacer reduced the decline to approximately 30%.

The result therefore suggests that reduced headspace is a major explanatory variable, rather than the brass spacer itself having a unique effect.

2: Does reducing headspace improve extraction uniformity, as judged visually from the bottomless-portafilter extraction and the spent puck?

The visual evidence indicates that it does.

The standard CI 200 IM screen showed particularly weak puck uniformity. In contrast, the CI 200 IM plus spacer, IMS SI 200 IM, and CI 35 WM plus spacer all showed substantially stronger puck-uniformity assessments.

The photographs also show a noticeably fragmented knocked-out puck with the standard CI 200 IM configuration, while the other configurations produced more intact puck discs. Because this was evaluated visually rather than through a quantitative imaging method, the result should be regarded as suggestive rather than definitive.

3: How does the spacer or altered shower-screen geometry affect extraction yield?

It does not systematically increase extraction yield.

The highest individual result was approximately 19.5% EY with the standard CI 200 IM screen at 9–10 bar. The spacer version reached approximately 19.2%, the IMS SI 200 IM about 19.3%, and the CI 35 WM plus spacer ranged from approximately 18.5% to 19.0%.

The experiment therefore provides no evidence that reducing headspace automatically raises extraction yield.

Instead, it demonstrates that a slightly lower extraction yield can coexist with better pressure behavior and better sensory performance.

4: How do the different spacer/screen configurations affect sensory attributes and overall taste score at approximately 6–7 bar and 9–10 bar extraction pressures?

The standard CI 200 IM configuration produced the weakest overall taste scores and displayed substantially more bitterness at high pressure.

Adding the spacer improved balance and raised taste score to roughly 4–4.5/10.

The IMS SI 200 IM performed better still, reaching approximately 5–5.5/10, with high acidity and sweetness and very little bitterness or astringency.

The strongest individual result was the IMS CI 35 WM plus spacer at 6–7 bar, at approximately 6/10. It combined high acidity and sweetness with almost no bitterness or astringency.

Increasing that configuration to 9–10 bar did not improve the cup and instead reduced its sensory score.

5: Which of the four tested configurations appears to provide the best overall compromise between hydraulic behavior, extraction uniformity, extraction yield, and taste?

There is no single winner on every metric.

The IMS CI 35 WM plus spacer produced the gentlest pressure decline and the highest individual sensory score, particularly at 6–7 bar, but required a reduced 14.5 g dose to avoid puck contact and did not provide the highest extraction yield.

The IMS SI 200 IM without a spacer appears to offer the strongest practical compromise: it produced a similarly gentler pressure decline, good visual puck uniformity, extraction yield close to the baseline, low bitterness and astringency, and one of the highest taste scores.

The CI 200 IM plus brass spacer nevertheless demonstrated the spacer's effectiveness clearly: compared with the otherwise similar standard CI 200 IM arrangement, it reduced the post-peak pressure decline, improved visual puck behavior, reduced undesirable sensory intensity, and increased the overall taste score.

The central lesson of the experiments is therefore that shower-screen geometry and headspace can significantly influence espresso behavior even when conventional extraction-yield measurements change only modestly. The experiments suggest that reducing the air space above the puck can stabilize the extraction after peak pressure and potentially produce a more uniform and better-tasting espresso, but reducing headspace too far introduces practical constraints such as puck-screen contact and the need to lower the dose.

Reneka micro-sieve vs VST and IMS precision baskets: Hydraulic, extraction and sensory effects in espresso

1. Introduction

In December 2019, Stéphane Ribes conducted a comparative espresso experiment using a Decent Espresso DE1 Pro v1.1 to investigate whether the choice of filter basket should depend on the characteristics, or in the author's wording the “quality,” of the coffee beans. The specific comparison was between a Reneka Micro-Sieve basket, a VST 15 g ridgeless precision basket, and an IMS precision basket. His presentation can be found here.

The experiment is particularly interesting because the three baskets differ substantially in construction. The IMS B702TFh22NT is specified as having 715 holes of 0.300 mm diameter. The Reneka Micro-Sieve is specified as having approximately 15,000 holes of 0.170 mm diameter, while the VST 15 g precision basket contains 727 holes, although the hole diameter is not provided in the presentation. The diagram also labels the Reneka at 40 mm and the IMS/VST at 49 mm, although it does not state unambiguously whether those dimensions refer to the complete basket bottom or the active perforated region.

Thus, the Reneka is not simply another conventional precision basket. It uses roughly 21 times as many holes as the IMS, with each opening substantially smaller. The experiment therefore compares two broadly conventional precision-basket designs, IMS and VST, with a fundamentally different micro-sieve architecture.

The central outcome of the experiment is a trade-off. The Reneka produced a much more stable extraction-pressure profile, but simultaneously caused a large reduction in measured extraction yield. Sensory evaluation nevertheless suggested that, for the coffee used in this experiment, this lower-extraction behavior could be advantageous when the VST and IMS baskets emphasized unpleasant roasting notes. The presentation also reports no major practical difference between the VST and IMS baskets.

This means that the study is not really asking which basket is universally “best.” It asks whether different hydraulic and extraction characteristics can make different baskets more suitable for different coffees.

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2. Questions asked

The presentation explicitly asks whether a different filter basket might be appropriate depending on bean “quality.” From the actual experimental design, this overarching question can be divided into five research questions:

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3. Method

Experimental design

The experiment used three filter baskets:

IMS B702TFh22NT: 715 holes, 0.300 mm diameter.

Reneka Micro-Sieve: approximately 15,000 holes, 0.170 mm diameter.

VST ridgeless precision basket, 15 g: 727 holes; hole diameter not specified.

Each basket was tested at two Mahlkönig EK43 S grinder settings:

Grind setting 1: EK1.2

Grind setting 2: EK1.3

Espresso equipment

The setup consisted of:

Decent Espresso DE1PRO v1.1

Red Cafelat 8.0 mm silicone group gasket

IMS SI 200 IM shower screen, without spacer

Mahlkönig EK43 S grinder

SSP High Uniformity burrs with Silver Knight coating.

Water

Montille water from Le Mont-Dore, France, was modified to 50 ppm as CaCO₃ alkalinity and 100 ppm as CaCO₃ total hardness using sodium carbonate and Epsom salts.

This is important because water composition strongly affects extraction and sensory perception. Holding it constant reduces one source of variability between basket conditions.

Coffee

The coffee shown in the protocol is La Candelilla, a honey-processed grain from Costa Rica, which was roasted (filter roast) roughly a month before the experiment.

Puck preparation

Preparation was deliberately standardized. Before every shot, the basket and shower screen were thoroughly dried with a clean tissue. Frozen beans were single-dosed and ground into a double-walled stainless-steel cup. The grounds were distributed using WDT with a Londinium tool and a Decent funnel, without tapping. Tamping was performed with a Force Tamper with a 58.5 mm flat base, applied twice consecutively.

Every shot used:

14.5 g ground coffee → 29 g espresso

giving a fixed 1:2 brew ratio.

Extraction and TDS measurements

TDS was measured with an Atago PAL refractometer, zeroed using SCAA water. Coffee samples were not additionally filtered, were measured at room temperature after thorough agitation, and each reported data point was the average of three to five refractometer measurements of the same coffee sample.

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4. Proceeding

The DE1 was programmed with a profile described as a mixture of a Londinium profile and a blooming shot. The extraction consisted of four phases, which are illustrated below:

Step 1 – Preinfusion

The profile uses an initial preinfusion at approximately:

94°C

6.0 mL/s

maximum duration of approximately 10 seconds

transition set to fast

advancement once pressure exceeds approximately 2.5 bar

The aim is to saturate the puck rapidly before entering the bloom.

Step 2 – Low-pressure bloom

The profile then enters a low-pressure bloom at approximately:

90°C

3.0 bar

15 seconds

The purpose of this stage is to maintain a relatively constant volume of the air pocket above the puck. The intention is to limit further damage to the puck surface when water flow is subsequently increased.

Step 3 – Flow rise

After the bloom, flow is increased toward approximately:

1.5 mL/s

over approximately 6 seconds

using a smooth transition

at approximately 90°C

This gradual increase is intended to avoid a sudden hydraulic shock to the coffee bed.

Step 4 – Flow hold

The final stage maintains approximately:

1.5 mL/s

at approximately 90°C

with the profile showing a maximum duration of 45 seconds. In practice, the shots terminate once the target beverage mass of 29 g is reached.

The significance of using flow priority is that flow is the principal controlled variable during the extraction phase. Pressure is therefore especially useful as a response variable: it indicates how much hydraulic resistance the puck-and-basket system develops while the machine attempts to impose the programmed flow.

The experiment then compares, for every basket and grinder setting:

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5. Results

5.1. Quantitative pressure and extraction-yield results

The measured results were:

The maximum pressures themselves are not dramatically different between baskets at a given setting. At EK1.2, all three peak close to 10 bar; at EK1.3, all three peak close to 7 bar.

The major difference emerges after the pressure peak.

At EK1.2:

IMS falls from 10.2 to 3.3 bar: a 6.9 bar decrease.

VST falls from 10.3 to 3.7 bar: a 6.6 bar decrease.

Reneka falls only from 9.8 to 8.5 bar: a 1.3 bar decrease.

Reneka therefore retains approximately 87% of its peak pressure, compared with about 32% for IMS and 36% for VST.

At EK1.3:

IMS falls from 7.2 to 3.0 bar: 4.2 bar.

VST falls from 6.8 to 3.3 bar: 3.5 bar.

Reneka falls from 7.0 to 5.7 bar: again only 1.3 bar.

Reneka retains approximately 81% of its peak pressure, compared with about 42% for IMS and 49% for VST.

This quantitatively confirms the presentation's main hydraulic observation: the Reneka produces a much softer pressure decline after peak pressure.

5.2. Interpretation of the pressure graphs

The six DE1 graphs below from on page 7 of Stéphane's presentation make this behavior particularly clear:

During preinfusion and bloom, the traces are broadly similar because the machine follows the same programmed sequence. The differences become pronounced when the main flow phase begins.

With IMS and VST, pressure rises sharply to a peak and then continuously collapses as the shot progresses. With the Reneka, pressure also peaks, but instead of collapsing, it reaches a comparatively stable plateau.

This distinction is reproducible at both grinder settings.

The pressure curves therefore suggest that the combined hydraulic resistance of the puck and Reneka basket changes much less during the latter portion of the extraction. The experiment does not, however, establish the exact physical mechanism responsible. Possible contributions could include basket geometry, flow distribution or the interaction of fines with the micro-sieve, but these mechanisms were not separately tested.

The important empirical observation is simply that the Reneka provides a much more constant pressure response when flow is prescribed.

5.3. Pressure stability does not mean higher extraction

One of the most important lessons from these results is that a stable or high pressure is not equivalent to high extraction.

Despite maintaining considerably more pressure throughout the latter part of the shot, the Reneka produces the lowest extraction yield by a large margin:

Reneka: 16.3–16.4%

IMS: 19.7–19.8%

VST: 19.8–20.0%.

The difference is approximately 3.4–3.7 percentage points, which corresponds to roughly a 17–19% relative reduction in extraction yield compared with the conventional precision baskets.

Because every shot uses 14.5 g of coffee and produces 29 g of beverage, the brew ratio is exactly 2:1. Using the conventional relationship between extraction yield, beverage mass, dose and TDS, the reported yields imply approximate beverage concentrations of:

Reneka: 8.15–8.20% TDS

IMS: 9.85–9.90% TDS

VST: 9.90–10.00% TDS

Thus the Reneka shots were not merely lower in extraction yield; at the same beverage mass, they were also substantially less concentrated.

This is crucial when interpreting the sensory result. The improved perceived clarity with the Reneka may result partly from producing a less highly extracted and less concentrated espresso, rather than from the micro-sieve selectively removing specific undesirable compounds.

5.4. Effect of the two grinder settings

Moving from EK1.2 to EK1.3 reduced peak pressure with all three baskets:

IMS: 10.2 → 7.2 bar

Reneka: 9.8 → 7.0 bar

VST: 10.3 → 6.8 bar.

The remarkable point is that extraction yield barely changed:

IMS: 19.8 → 19.7%

Reneka: 16.4 → 16.3%

VST: 19.8 → 20.0%

Within this relatively small adjustment range, the basket design had a far larger effect on extraction yield than the grinder-setting change.

At the same time, sensory preference changed considerably, particularly for the Reneka and VST. This demonstrates that a virtually identical extraction-yield number does not guarantee an identical-tasting espresso.

5.5. IMS versus VST

IMS and VST behaved very similarly.

At EK1.2 they produce almost identical peak pressures, similarly steep post-peak declines, and exactly the same reported extraction yield of 19.8%.

At EK1.3 the pattern remains close: 7.2 versus 6.8 bar maximum pressure, 3.0 versus 3.3 bar final pressure, and 19.7 versus 20.0% extraction yield.

This directly supports Ribes' statement that there were “no major differences between the VST 15g and IMS precision filter baskets.”

The basket comparison is therefore primarily Reneka versus conventional precision baskets, rather than a meaningful IMS-versus-VST contest.

5.6. Post-shot puck photographs

The page 6 photographs of the presentation, illustrated below, document the puck surface, basket after extraction, espresso and removed spent puck for each condition.

At EK1.2, all three removed pucks appear comparatively intact. At EK1.3, the IMS puck shown in the photograph is visibly fractured, whereas the photographed Reneka and VST pucks remain more intact.

This should not be treated as direct proof of channeling. A puck can crack during depressurization or removal. The photographs are therefore useful supporting observations, but the pressure and extraction measurements provide stronger evidence than the appearance of a single spent puck.

5.7. Sensory results

The final slide in Ribes' presentation compares six sensory attributes:

body, acidity, bitterness, sweetness, flavor and astringency, together with an overall taste score on a 0–10 scale. It is illustrated below:

The exact taste-score values are not printed numerically, so the following values are approximate readings of the marker positions.

For EK1.2:

IMS: approximately 4/10

Reneka: approximately 4/10

VST: approximately 3/10

For EK1.3:

IMS: approximately 4.5/10

Reneka: approximately 6–6.5/10

VST: approximately 5/10

The clearest visual result is therefore the relatively high preference for Reneka at EK1.3, while VST at EK1.2 appears to be the least favored condition.

The intensity plots add nuance. Across the conditions, acidity is generally medium to high, whereas sweetness, flavor intensity and astringency occupy lower portions of their scales. The Reneka EK1.3 cup combines relatively strong acidity and bitterness with comparatively low astringency, yet obtains the highest overall taste score.

This is significant because it shows that the preference for the Reneka was not simply a matter of minimizing bitterness. Ribes instead characterizes the result as higher flavor clarity, specifically in a situation in which the VST or IMS shots displayed unpleasant roasting notes.

In other words, the sensory advantage appears to concern balance and clarity rather than the absolute intensity of any single taste dimension.

5.8. The central trade-off

Taken together, the results identify a clear trade-off:

IMS/VST

Higher extraction yield: approximately 19.7–20.0%.

Much larger pressure decline during extraction.

Similar performance to one another.

For the coffee used, greater expression of undesirable roasting notes in at least some conditions.

Reneka

Much lower extraction yield: approximately 16.3–16.4%.

Far more stable post-peak pressure.

Lower beverage concentration at the same brew ratio.

In this particular coffee, potentially better flavor clarity and, at EK1.3, the highest sensory score.

Consequently, the Reneka cannot simply be described as technically “better.” It produces a different extraction regime.

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6. Conclusion

The experiments show that basket architecture can substantially change espresso behavior even when the coffee dose, beverage mass, grinder, puck preparation, water and machine profile are held constant. The most striking result is the separation between hydraulic behavior and extraction: the Reneka maintains much more pressure throughout the shot while extracting considerably less coffee material.

For the specific Costa Rican coffee tested, that lower-extraction regime was not necessarily undesirable. On the contrary, it could reduce the prominence of unpleasant roasting characteristics and yield a cup perceived as clearer and, in the best-performing condition, more enjoyable.

The data therefore argue against the idea that the basket with the highest extraction yield or the most stable pressure is automatically superior. Basket choice can be understood as another variable for shaping extraction and sensory expression.

The five questions posed at the beginning can now be answered as follows.

1. Does the Reneka Micro-Sieve produce a different pressure profile from the IMS and VST precision baskets when the espresso machine is operated in flow-priority mode?

Yes. This is the strongest result of the study. Reneka shows only a 1.3 bar decline from peak to final pressure at both grinder settings, whereas the IMS and VST lose approximately 3.5–6.9 bar. Reneka retains roughly 81–87% of peak pressure, compared with approximately 32–49% for IMS/VST. The pressure curves consequently show a clear plateau with Reneka and a pronounced decline with the two conventional precision baskets.

2. Does the Reneka Micro-Sieve change extraction yield when dose, beverage mass, preparation and grinder setting are held constant?

Yes, dramatically. Reneka produces only 16.3–16.4% extraction yield compared with approximately 19.7–20.0% for IMS and VST. The loss is around 3.5 percentage points, or roughly 17–19% in relative terms.

At the fixed 1:2 brew ratio, this also means that the Reneka shots are substantially less concentrated.

Therefore, the stable pressure provided by the Reneka must not be interpreted as evidence of stronger or more complete extraction.

3. Do the hydraulic and extraction differences translate into a different sensory profile or overall taste quality, particularly when unpleasant roasting notes are present?

For the coffee used in this experiment, apparently yes.

Ribes reports higher flavor clarity with the Reneka when unpleasant roasting notes were present with IMS or VST. The sensory graph also gives Reneka at EK1.3 the highest overall taste score of the six conditions.

However, this result must be interpreted carefully. Because the Reneka also produces much lower EY and TDS, the experiment does not establish whether the sensory improvement is caused specifically by the micro-sieve architecture or simply by the lower degree of extraction and concentration that the architecture produced.

4. Is there a meaningful difference between the VST 15 g and IMS precision baskets?

Not in this experiment.

Their pressure profiles, extraction yields and general behavior are very close. The author explicitly concludes that there are no major differences between them.

For practical interpretation of this dataset, IMS and VST can therefore be treated as broadly equivalent conventional precision-basket references.

5. Do the results support choosing a filter basket according to the characteristics or “quality” of the beans?

They support the idea as a hypothesis and practical strategy, but not yet as a universal rule.

For a coffee that tastes clean and pleasant at an extraction yield around 20%, IMS or VST may be preferable because they achieve substantially more extraction.

For the particular coffee used here, where that higher extraction could reveal unpleasant roasting notes, the Reneka's lower-extraction behavior appeared capable of producing greater clarity and a better sensory result.

The most defensible conclusion is therefore not “Reneka is better”, but: Reneka, IMS and VST create different extraction conditions, and those differences may make one basket more appropriate than another depending on how a particular coffee responds to extraction.

The presentation consequently provides evidence that the filter basket can be treated as an active extraction variable rather than merely as a passive container for the coffee bed. At the same time, broader testing across coffees, roast levels, matched extraction yields and blind replicated tastings would be required before establishing a general rule for selecting baskets according to bean quality.

IMS CI 200 IM vs IMS SI 200 IM: Effects on espresso pressure, Extraction Yield, puck structure, and radial uniformity

1. Introduction

In March 2020, Stéphane Ribes compared two IMS shower screens—the IMS CI 200 IM and IMS SI 200 IM—on a Decent Espresso DE1PRO v1.1. The slides of the presentation can be found here.

The purpose of the experiment was not simply to determine whether one screen produced a higher extraction yield, but to examine how changing the shower screen affected the complete espresso system: pressure development, pressure decline during a flow-controlled extraction, extraction yield (EY), puck behavior after brewing, sensory properties, and the radial uniformity of extraction from the center of the puck to its outer edge.

The distinction is important because a shower screen can affect more than the visible distribution of water. By changing the geometry above the coffee puck and the available clearance for puck expansion, it can influence how the puck wets, swells, resists flow, and maintains its structure during extraction. Those changes can then be reflected in the machine's pressure curve and in how evenly different parts of the coffee bed are extracted.

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2. Questions asked

The experiment can be organized around five principal questions:

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3. Method

Espresso equipment

The experiment was performed on a Decent Espresso Machine DE1PRO v1.1. The only component intentionally compared was the shower screen:

IMS CI 200 IM

IMS SI 200 IM

Grinding was performed using a Mahlkönig EK43 S fitted with SSP "High Uniformity" burrs with Silver Knight coating.

A VST 15 g ridgeless filter basket was used, with a target brew ratio of 1:3.

Water

The test water was Montille water from Le Mont-Dore, France. It was adjusted to 50 ppm as CaCO₃ alkalinity and 125 ppm as CaCO₃ total hardness.

The mineral adjustment was made using sodium carbonate and Epsom salts.

Controlling the water composition was important because mineral composition can influence extraction and therefore had to remain constant while the shower screens were compared.

Thermal preparation

The portafilter was preheated in a kettle to 80°C.

Before every shot, both the filter basket and shower screen were completely dried with a clean tissue. This eliminated residual water as a source of variation in puck preparation and initial wetting.

All extraction stages were run with a target coffee temperature of 90°C.

Coffee preparation

The beans were stored frozen and single-dosed. Each dose was ground into a double-walled stainless-steel cup.

Puck preparation was deliberately standardized:

The extensive preparation protocol was intended to minimize distribution and tamping inconsistencies so that differences observed during extraction would be more closely associated with the shower-screen configuration.

Extraction profile

A hybrid "Lever-Blooming" profile was used. It combined elements of a Londinium-style lever profile and a blooming extraction.

Here's the screens of the individual profile steps:

The programmed sequence was as follows:

Step 0 – "Lock portafilter!"

90°C

0.0 bar

5 seconds

Fast transition

Step 1 – Preinfusion

90°C

Flow: 6.0 mL/s

Maximum programmed duration: 20 seconds

Fast transition

The machine moved to the next step once pressure exceeded 2.0 bar

Thus, the 20-second value acted as a maximum rather than necessarily determining the actual preinfusion duration.

Step 2 – Low-pressure bloom

90°C

Pressure target: 3.0 bar

Duration: 6 seconds

Fast transition

This created a pressurized blooming period after initial saturation.

Step 3 – Flow rise

90°C

Target flow: 2.2 mL/s

Duration: 10 seconds

Smooth transition

Rather than abruptly imposing the extraction flow, the machine gradually increased flow to the final target.

Step 4 – Hold flow

90°C

Flow: 2.2 mL/s

Maximum duration: 45 seconds

Fast transition setting

The extraction then continued under flow priority until the target beverage output was obtained.

Extraction-yield measurements

Total Dissolved Solids were measured with an Atago PAL refractometer.

The instrument was zeroed using the same adjusted Montille water used for brewing. Coffee samples were not filtered before measurement.

Before measurement:

samples were allowed to reach room temperature;

they were vigorously stirred;

each reported data point represented the average of three to five refractometer measurements of that coffee sample.

TDS measurements were then used to determine Extraction Yield.

Radial extraction measurements

The experiment also examined whether the puck was extracted uniformly from its center to its circumference.

Essentially, the puck was divided into three concentric regions:

center

middle

outside

Ribes places the center of the basket at 0 mm and the basket wall at approximately 29 mm radius, with the central sampling region extending to approximately 18 mm before the intermediate and outer annular regions.

A local EY was determined for each radial zone:

EY puck center

EY puck middle

EY puck outside

The final espresso itself was measured separately to obtain the overall beverage EY.

This allowed the experiment to distinguish between a shot having a high average EY and a shot extracting uniformly throughout the puck. Those are not necessarily the same thing.

4. Proceeding

Three principal shots were used for the shower-screen comparison. Here's the charts:

Shot 1: IMS CI 200 IM reference

The reference shot used:

IMS CI 200 IM

Dose: 14.5 g

EK43 setting: EK2.3

Overall EY: 21.7%

This established the hydraulic and extraction behavior of the CI screen.

During the main extraction stage, pressure rose to approximately 6.4 bar. Once the target flow was established, pressure fell comparatively rapidly and eventually approached roughly 2.5 bar.

Shot 2: IMS SI 200 IM at identical dose and grind

The screen was then changed to the IMS SI 200 IM, while the two most important puck-resistance variables were deliberately left unchanged:

Dose: 14.5 g

Grind: EK2.3

Overall EY: 22.3%

This was the direct same-dose, same-grind comparison.

The resulting pressure curve was dramatically different. Instead of peaking around 6–7 bar, pressure climbed to almost 12 bar. It subsequently decreased but remained at approximately 8 bar late in the extraction.

This demonstrated that merely substituting the SI 200 screen substantially altered the hydraulic behavior.

However, because pressure was now very different, Shot 2 could not by itself provide a clean comparison of the screens under equivalent extraction pressure.

Shot 3: IMS SI 200 IM adjusted to approximately match pressure

A third shot therefore retained the SI 200 screen but changed the recipe to reduce puck resistance and bring the peak pressure closer to that of Shot 1:

Dose reduced from 14.5 g to 14.0 g

Grind changed from EK2.3 to the coarser EK2.4

Overall EY: 22.0%

Peak pressure was approximately 7.2 bar, much closer to Shot 1.

The critical comparison was then between:

Shot 1: CI 200, 14.5 g, EK2.3

Shot 3: SI 200, 14.0 g, EK2.4

This permitted the two pressure curves to be compared in a similar range while acknowledging that dose and grind had been deliberately changed.

Post-extraction puck examination

After every shot, the basket, puck and shower-screen contact were visually inspected.

The physical condition of the SI-screen pucks differed noticeably from the CI-screen puck.

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5. Results

5.1. The SI 200 produced much higher pressure at the same dose and grind

The most immediate result came from comparing Shots 1 and 2.

Both shots used:

14.5 g coffee

EK2.3 grind setting

the same basket

the same puck-preparation procedure

the same extraction profile

Yet their pressure curves were radically different.

With the CI 200, peak extraction pressure was approximately 6.4 bar.

With the SI 200, pressure climbed to almost 12 bar.

The SI screen therefore caused the system to exhibit substantially greater effective hydraulic resistance under otherwise comparable preparation conditions.

The experiment does not establish that the metal mesh itself was simply "more restrictive." The later puck observations indicate that altered shower-screen-to-puck clearance and the resulting interaction with an expanding puck are also relevant. What can be stated directly is that changing to the SI screen dramatically altered the pressure response.

5.2. Matching pressure required a lower dose and a coarser grind with the SI 200

To bring the SI-screen shot back into approximately the same pressure range as the CI-screen reference, both resistance-related variables were reduced:

dose: 14.5 g → 14.0 g

grind: EK2.3 → EK2.4, i.e. coarser

This produced a peak of about 7.2 bar.

The need to make those changes reinforces how strongly the screen configuration affected shot hydraulics.

5.3. Pressure declined more gently with the SI 200

Once peak pressures were brought into a comparable range, another difference became visible.

With the CI 200, pressure fell relatively sharply after its peak. The curve declined from approximately 6.4 bar toward roughly 2.5 bar.

With the adjusted SI 200 shot, pressure declined more gradually, from roughly 7.2 bar toward approximately 4.5–5 bar late in the shot.

Thus, the SI 200 did not merely change the peak pressure. It was also associated with a gentler pressure decrease during the constant-flow stage.

A gentler decline means that the puck maintained resistance to water flow more effectively as the extraction progressed.

5.4. Overall extraction yield was slightly higher with the SI 200

The measured overall extraction yields were:

At identical dose and grind, the SI screen yielded 0.6 percentage points more extraction than the CI screen, although that comparison also involved a radically higher pressure.

The more meaningful pressure-adjusted comparison was Shot 1 versus Shot 3. Despite using both a lower dose and a coarser grind, the SI shot still reached an EY of 22.0%, versus 21.7% with the CI screen.

The difference was small—+0.3 EY percentage points—but notable because the coarser grind would not ordinarily be chosen to maximize extraction.

5.5. Taste differences were minor

The experiment reported no major taste difference between Shot 1 and Shot 3.

The only sensory distinction noted was slightly lower acidity with the IMS SI 200.

Consequently, the measurable changes in pressure behavior and radial extraction were larger than the observed sensory difference in this particular comparison.

5.6. The SI 200 produced drier, more solid spent pucks

The physical pucks provided another clear distinction.

After extraction, the pucks produced with the IMS SI 200 screen were drier and more solid than the puck produced with the IMS CI 200. Here's the photos showing the pucks, in which the spent puck from the IMS CI 200 IM shower screen is noticeably wetter:

This suggests that the SI configuration constrained the puck differently during extraction and helped it retain a more coherent structure after brewing.

5.7. Puck swelling caused contact with the SI 200 screen

The dry puck initially had only an estimated 1 mm of clearance below the IMS SI 200 screen.

During brewing, the grounds were estimated to swell by more than 3 mm.

Because the swelling exceeded the initial clearance, the coffee puck necessarily contacted the shower screen during extraction.

This interaction was strong enough that, after Shots 2 and 3, the puck remained stuck to the shower screen when the portafilter was removed. The imprint of the shower screen is visible in the pucks of shot 2 and 3:

This is an important mechanical result. It provides a plausible physical context for both the higher resistance and the greater stability of the pressure curve: with very little headspace, the swelling puck becomes mechanically constrained by the shower screen instead of expanding freely upward.

5.8. All three shots remained radially non-uniform

The radial measurements reveal that none of the screens created perfectly uniform extraction.

The local EYs were:

The dominant pattern is immediately visible: the center and middle of the puck extracted much more strongly than the outer edge.

For the CI 200 reference:

center: 24.7%

middle: 24%

outside: only 16%

The center-to-edge difference was therefore approximately 8.7 EY percentage points.

This indicates severe underextraction around the circumference of the coffee bed even though the average beverage EY was a respectable 21.7%.

5.9. The SI 200 improved the outer-puck extraction

With the adjusted SI-screen shot:

center: 24.6%

middle: 24%

outside: 18%

The center and middle values were essentially unchanged relative to the CI reference, but the outer section rose from 16% to 18%.

The center-to-edge spread consequently decreased:

CI 200: 24.7 − 16 = 8.7 points

SI 200 adjusted: 24.6 − 18 = 6.6 points

The radial spread therefore narrowed by approximately 2.1 EY percentage points.

The improvement did not come from extracting the already highly extracted center harder. Instead, most of the gain appeared at the region that needed it most: the perimeter of the puck.

This is why the slightly higher overall EY of the SI-screen shot is consistent with a more uniform radial extraction.

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6. Conclusion

Taken together, the experiment indicates that changing from the IMS CI 200 IM to the IMS SI 200 IM alters the mechanical interaction between the shower screen and puck, substantially changes shot hydraulics, and appears to modestly improve extraction efficiency primarily by reducing underextraction at the outer edge of the coffee bed. The findings can be summarized by answering the original questions directly:

1. At the same coffee dose and grind setting, does replacing the IMS CI 200 IM with the IMS SI 200 IM change the extraction-pressure profile?

Yes. At 14.5 g and EK2.3, the CI 200 produced a peak pressure of roughly 6.4 bar, whereas the SI 200 reached almost 12 bar. The screen change therefore produced a very large increase in effective puck resistance and fundamentally altered the pressure curve.

2. When dose and grind are adjusted to obtain a comparable peak pressure, does the IMS SI 200 IM still alter the pressure decline or total extraction yield?

Yes. Reducing the SI-screen dose to 14.0 g and grinding more coarsely at EK2.4 brought peak pressure back to approximately 7.2 bar. Even under those conditions, the SI shot showed a noticeably gentler pressure decline than the CI reference. Its overall EY was also slightly higher: 22.0% versus 21.7%, despite the coarser grind and lower dose.

3. Does changing from the IMS CI 200 IM to the IMS SI 200 IM produce a noticeable difference in taste?

Only a small one in this experiment. No major sensory difference was reported between the pressure-comparable CI and SI shots. The SI 200 was described as producing slightly lower acidity, but the overall taste profiles were otherwise similar.

4. Does the IMS SI 200 IM change the physical condition and behavior of the coffee puck after extraction?

Yes, substantially. The SI-screen pucks were drier and more solid after extraction.

The dry puck had only about 1 mm of clearance below the SI screen, while the grounds were estimated to swell by more than 3 mm during brewing. The expanding puck therefore contacted the shower screen, and in both SI shots the puck remained stuck to the screen when the portafilter was removed.

This reduced clearance and mechanical constraint of the swollen puck provide an important physical context for the SI screen's higher pressure and more gradual pressure decline.

5. Does the IMS SI 200 IM improve the radial uniformity of extraction between the center, middle, and outer regions of the puck?

Yes, although the extraction remains significantly non-uniform. The central and middle regions were essentially unchanged, but the extraction of the outer puck increased by approximately 2 EY percentage points.

Therefore, the principal extraction advantage of the IMS SI 200 IM was not a further increase in the already highly extracted center. Instead, it reduced some of the severe extraction deficit at the perimeter of the puck. This more even radial distribution is the most plausible explanation offered by the experiment for why the SI 200 achieved a slightly higher overall extraction yield even when it was paired with a lower dose and coarser grind.

The IMS SI 200 IM therefore appears to provide greater puck constraint, higher hydraulic resistance, a more stable late-shot pressure curve, a drier and more coherent spent puck, and moderately better radial extraction uniformity than the IMS CI 200 IM under the conditions tested. Its improvement was measurable but not absolute: the outer edge remained significantly less extracted than the center, and the observed sensory advantage was small.

10g espresso dose: better in a 7g or in a 15g basket?

1. Introduction

In May 2020, Stéphane Ribes documented an experiment asking a practical espresso question: when using a 10 g coffee dose, is it better to use a nominal 7 g single basket or a 15 g double basket? The slides of his presentation can be found here . The reference configuration was a VST 15 g basket, while the alternative was the Decent 7 g basket.

This was not a simple test in which the basket alone was changed and every other parameter held fixed. Instead, the objective was to determine what changes were necessary to make a 10 g dose function sensibly in the geometrically very different 7 g basket. The experiment therefore progressively modified shower-screen geometry, grind size, extraction flow and brew ratio, then compared extraction yield (EY), total dissolved solids (TDS), pressure behavior and qualitative cup characteristics.

The central result is clear: a 10 g dose can produce a pleasant espresso in the 7 g single basket, but it requires substantial retuning and still does not reproduce the extraction performance of the 15 g basket. The final 7 g-basket shot reached only 12.1% EY and 5.5% TDS, versus 20.0% EY and 7.6% TDS in the 15 g reference. The 7g basket also produced less crema and a thinner body.

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2. Questions asked

Ribes' presentation addresses five closely related questions:

These questions reconstruct the experimental logic of the slides from the stated comparison, the tuning sequence and the reported observations.

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3. Method

Experimental setup and preparation

The experiment used a Decent Espresso DE1PRO v1.1 fitted with a red Cafelat 8.0 mm silicone gasket. The following two basket/screen combinations were compared, whereby the 7g basket was called single filter basket and the 15g basket double filter basket in the presentation:

The different shower screens were deliberate. Ribes wanted to maintain approximately 4 mm of clearance between the coffee puck and shower screen in both configurations. The CI 200 screen was therefore used with the much shallower 7 g basket.

Grinding was performed with a Mahlkönig EK43 S fitted with SSP “High Uniformity” burrs with Silver Knight coating. Water was Montille water from Le Mont-Dore, France, adjusted with sodium carbonate and Epsom salts to 40 ppm as CaCO₃ alkalinity and 90 ppm as CaCO₃ total hardness.

Portafilters were preheated to 70 °C in a kettle. The basket and shower screen were completely dried before every shot. Beans were single-dosed and ground while frozen into a double-walled stainless-steel cup. For distribution, Ribes used WDT directly in the basket with a Londinium tool and Decent funnel, followed by gentle raking to create a uniform surface. For tamping, he used a Force Tamper with a 58.5 mm smooth flat base at 33 lb, rather than its 24 lb standard force.

TDS was measured with an Atago PAL refractometer, zeroed using the adjusted Montille water. Coffee samples were not filtered, were vigorously stirred and measured at room temperature. Each reported TDS data point was the average of three to five refractometer measurements of the same coffee sample.

Coffee

The package shown on page 6 of the presentation identifies the coffee as OR Coffee Roastery, Brasil – Sitio das Pedras, processed as a fermented natural and roasted as a filter roast.

Important experimental limitation

This is best understood as a tuning comparison, not a strictly controlled one-variable basket experiment. Changing from the 15 g to the 7 g basket also required changes in shower screen, grind, flow profile and eventually brew ratio. Consequently, the experiment shows how the two systems perform when individually adapted, but it cannot attribute every difference exclusively to basket geometry.

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4. Proceeding

Establishing the 15 g-basket reference

The 10 g dose in the VST 15 g basket was used as the reference. Its principal settings and results were:

IMS SI 200 screen

EK43 grind setting EK1.1

approximately 2.7 mL/s extraction flow

approximately 1:2.6 brew ratio

7.6% TDS

20.0% EY

The graph of the reference shot shows a controlled initial flow/preinfusion phase followed by extraction. Pressure builds progressively during the extraction rather than immediately jumping to an extreme value. This became the hydraulic behavior Ribes attempted to approximate with the 7g basket.

Here's the chart of the 15g shot, which he tried to replicate with the 7g basket:

Step 1: adapting the grind to the 7 g basket

The first major problem appeared as soon as the same EK1.1 grind was used in the 7 g basket. Here's the first shots with the 7 g basket, with gradually adjusted grind settings:

The 7 g basket has a much narrower perforated section: approximately 29 mm in diameter compared with 49 mm for the double basket. Ribes estimates that its perforated surface area is therefore approximately 65% lower.

That figure is also geometrically consistent with the indicated diameters:

(29/49)^2≈0.35

so the smaller basket has only about 35% of the perforated area, or roughly 65% less.

The practical consequence was very high hydraulic resistance. In the pressure plots above it's visible that using EK1.1 in the 7 g basket drives pressure rapidly to a very high plateau. Progressively coarsening the grind changes the hydraulic behavior, as visible in the charts above. For easier comparison, the resulting EY are also listed below:

The final required setting was EK2.2, corresponding in the slides to approximately a 90 µm burr gap, compared with approximately 45 µm at EK1.1. In other words, the burr gap had to be approximately doubled.

An important chart-level observation follows from these values: coarsening the grind solved a hydraulic problem, but it did not solve the extraction-yield problem. Across the four 7 g-basket grind settings, EY remained clustered around 12.3–12.6%. It never approached the reference value of 20%.

Ribes interprets the need for such a coarse grind primarily as a consequence of the much smaller perforated area of the single basket. This is presented as a likely explanation rather than demonstrated as a separate causal test.

Step 2: reducing extraction flow

Even at EK2.2, pressure remained undesirable at the higher extraction flow. The next intervention was therefore to reduce extraction flow from 2.7 mL/s to 1.7 mL/s.

The purpose was explicitly hydraulic: reduce extraction pressure and prevent channeling and spraying. The length of the flow ramp was also reduced so that the rate at which water flow increased remained approximately constant.

Below are the charts comparing shots 8, 9 and 10 for reference:

The charts above are particularly informative here. At 2.7 mL/s, the green pressure trace rises very steeply late in the shot and approaches the high end of the plotted pressure range. At 1.7 mL/s, the pressure trajectory becomes substantially lower and smoother, peaking at roughly the 6-bar region rather than approaching roughly 9 bar.

Yet TDS and EY remain exactly the same in the reported measurements: 4.8% and 12.4%.

That means the reduction in flow was valuable primarily for hydraulic stability and pressure control, rather than because it directly increased extraction.

Step 3: shortening the brew ratio

With extraction yield still low, Ribes then changed the output mass instead of trying to force higher extraction from the puck.

Shot 10 (shown above under step 2) retained the 1.7 mL/s flow but stopped at 22 g out from 10 g in, giving a 1:2.2 brew ratio, compared with 26 g / 1:2.6 previously:

1.7 mL/s

10 g in, 22 g out

brew ratio 1:2.2

27 s

TDS 5.5%

EY 12.1%

This produces one of the most important distinctions in the experiment: concentration and extraction yield are not the same thing.

Using the standard espresso EY relationship as an interpretive check,

Shot 9 gives approximately: 26×0.048/10≈12.5%

while Shot 10 gives: 22×0.055/10≈12.1%

So the shorter shot did not extract more material from the coffee. In fact, EY decreased slightly. What it did was put a similar amount of extracted coffee solids into less beverage, thereby raising concentration from 4.8% to 5.5%.

That increased concentration appears to have helped the sensory result. Ribes describes the final shot as more balanced, brighter and no longer bitter relative to the previous shot.

Visual assessment

In his presentation, Ribes included photographs of the two preparations side by side, apparently documenting the grounds/puck before extraction, the tamped surface, the espresso in the cup, the spent puck and the basket after puck removal.

The cup photographs qualitatively support the explicit observation elsewhere in the deck that the 7 g configuration produced less crema. Ribes also reports a thinner body with the 7 g basket.

The knocked-out 7 g puck also appears less intact around its perimeter than the 15 g puck, although Ribes does not explicitly interpret puck integrity, so this should not be treated as a measured result.

One further documentation gap should be noted: the presentation shows shots 0–4 and then 8–10. Shots 5–7 are not shown, so the complete tuning path between the grind-adjustment phase and the final flow experiments cannot be reconstructed.

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5. Results

Final tuned comparison

In his presentation, Ribes reported that adapting the 10 g dose to the 7 g basket required substantial changes relative to the VST 15 g reference: maintaining roughly 4 mm puck-to-screen clearance with an IMS CI 200 shower screen, grinding much coarser from EK1.1 to EK2.2, lowering the extraction flow rate to reduce pressure and limit channeling and spraying, and shortening the flow ramp. Even after these adjustments, extraction performance remained markedly lower: extraction yield fell from 20.0% to 12.1% and TDS from 7.6% to 5.5%. Reducing the brew ratio from 1:2.6 to 1:2.2 partly compensated for the low extraction yield by increasing beverage concentration and produced what Ribes described as a more balanced and quite pleasant shot. However, the 7 g basket still produced less crema and a thinner body than the 15 g reference.

Magnitude of the extraction difference

The final 7 g-basket EY of 12.1% is 7.9 percentage points below the 20.0% reference. In relative terms, it represents only about 60.5% of the reference extraction yield, or a roughly 39.5% reduction.

Similarly, TDS falls from 7.6% to 5.5%, a decline of 2.1 percentage points, or roughly 28% relative to the reference.

The smaller brew ratio partly compensates for the low extraction by concentrating the beverage, but it cannot fully recover the concentration of the double-basket shot. This is exactly what Ribes means by saying that shortening the ratio could “partly offset” the low EY's impact on TDS.

What the charts collectively demonstrate

The sequence of DE1 plots reveals three separate phenomena.

First, basket geometry changes puck hydraulics dramatically. The narrow 29 mm perforated region in the single basket is substantially more restrictive, requiring a grind that would normally be considered extremely coarse relative to the double-basket reference.

Second, hydraulic optimization and extraction optimization are not identical. Moving from EK1.1 to EK2.2 and then from 2.7 to 1.7 mL/s makes the single basket easier to control, lowers pressure and is intended to reduce channeling and sprays, but EY remains at about 12%.

Third, brew ratio can modify cup concentration independently of extraction yield. Shortening the output from 26 to 22 g raises TDS from 4.8 to 5.5%, even though EY falls slightly from 12.4 to 12.1%. This is why the final shot can become more satisfying despite the underlying extraction remaining low.

This distinction is the most useful general lesson contained in the deck: a better-tasting espresso after a recipe adjustment does not necessarily mean that extraction yield has increased.

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6. Conclusion

Taken together, the experiment supports the following answers to the questions posed above:

1. For a 10 g dose, can the 7 g Decent basket produce a shot comparable to the VST 15 g reference basket?

It can produce a drinkable and even pleasant shot, but it does not match the reference in extraction performance. The optimized single-basket (7g) shot reached 12.1% EY and 5.5% TDS, whereas the double-basket (15g) reference reached 20.0% EY and 7.6% TDS. It also had less crema and thinner body.

Thus, “comparable” is true only in the sense that the single basket can be tuned into a balanced beverage. It is not comparable in terms of EY, TDS or body.

2. What mechanical and extraction-profile changes are required to make the 7 g basket workable?

Several large changes were required: an IMS CI 200 screen to maintain roughly 4 mm headspace, a move from EK1.1 to EK2.2, a lower extraction flow of 1.7 instead of 2.7 mL/s, a shorter flow ramp, and eventually a 1:2.2 instead of 1:2.6 brew ratio.

The 7g basket therefore cannot simply replace the 15g basket while keeping the same recipe.

3. How does the much smaller perforated area of the 7 g basket affect grind requirements and extraction hydraulics?

Ribes attributes the approximately 65% reduction in perforated area to a major increase in hydraulic resistance. The practical response was to double the approximate burr gap from 45 to 90 µm.

The pressure charts support this interpretation: finer settings in the single basket generate very high pressures, while the much coarser EK2.2 grind produces a more manageable flow path.

4. What do a lower extraction flow rate and a shorter brew ratio do to pressure, TDS, extraction yield and taste?

Reducing flow from 2.7 to 1.7 mL/s substantially reduces extraction pressure and stabilizes the hydraulic profile, while the measured TDS and EY of the compared shots remain unchanged at 4.8% and 12.4%. The flow change therefore functions primarily as pressure/channeling control.

Reducing the brew ratio from 1:2.6 to 1:2.2 then increases TDS from 4.8% to 5.5%, while EY remains essentially unchanged or slightly lower, at 12.1%. The espresso consequently becomes more concentrated without extracting more total soluble material. Sensory balance improves, with Ribes describing the final shot as brighter and no longer bitter.

5. Under the tested conditions, which basket is the more suitable choice for a 10 g espresso dose?

If the objective is extraction efficiency, concentration, crema and body, the 15 g VST double basket is clearly the stronger configuration in this experiment. It achieves 20% EY and 7.6% TDS with substantially less extreme recipe adaptation.

The 7 g single basket remains a viable alternative when a smaller, concentrated beverage is desired, but it demands much coarser grinding, lower flow and a shorter ratio, while still producing only about 12% EY. Its advantage in this experiment is therefore not superior extraction but the ability, after extensive tuning, to produce a balanced and quite pleasant 10 g-dose espresso despite its low extraction yield.

The broader implication should be kept narrow: this research provides a strong case study of how basket geometry, grind resistance, pressure, flow, extraction yield and beverage concentration interact, but it does not establish a universal rule for every single versus double basket. The evidence applies directly to the specific Decent/VST baskets, coffee, grinder, water and preparation protocol tested here.

Effect of Development Time Ratio (DTR) on Kaffelogic-roasted espresso: a comparison of 10% and 15% DTR

Introduction

In May 2020, Stéphane Ribes conducted research comparing different Development Time Ratios on his Kaffelogic Nano 7 roaster. The slides of his presentation can be found here.

The experiment compares two 90 g coffee roasts produced using the same “LightSide” roast profile but different Development Time Ratios (DTR): 10% and 15%. The roasted coffees were then prepared as espresso on a Decent Espresso machine and evaluated through extraction data, pressure/flow graphs, TDS and extraction-yield measurements, and sensory comparison.

The central purpose is therefore not simply to compare two roast curves. It is to investigate how extending development after first crack affects the coffee as an espresso: its physical extraction behavior, measured concentration and yield, and ultimately its sensory character.

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2. Questions asked

The following questions can be inferred from Ribes' experiments:

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3. Method

Coffee

The coffee used was a washed, green Yirgacheffe, variety Kurume, from Mr. Tessema Edima in Ethiopia.

Roasting equipment and experimental variable

Both batches were roasted on a Kaffelogic Nano 7:

Roast profile: “LightSide”

Batch size: 90 g

The experimental variable was DTR.

From those times, the actual development periods can also be calculated:

Roast 1: 8:24 − 7:33 = 51 seconds

Roast 2: 8:46 − 7:27 = 79 seconds

Thus Roast 2 had 28 seconds more post-first-crack development, approximately a 55% increase in absolute development time. The total roast itself was only 22 seconds longer, because first crack occurred six seconds earlier in Roast 2.

The roast-end temperature increased by 3°C, from 215°C to 218°C. Weight loss increased by 1.1 percentage points, from 12.1% to 13.2%.

Espresso equipment

The setup of Ribes' experiment consisted of:

Decent Espresso DE1PRO v1.1

Red Cafelat 8.0 mm silicone gasket

IMS SI 200 IM shower screen

Mahlkönig EK43 S grinder

SSP “High Uniformity” burrs with Silver Knight coating

VST 22 g ridgeless basket

The Force Tamper with 58.5 mm smooth flat base

Tamping force set to 33 lb, compared with the normal 24 lb setting.

Water

Montille water from Le Mont Dore, France, was adjusted to 40 ppm as CaCO₃ alkalinity and 90 ppm as CaCO₃ total hardness.

Sodium carbonate and Epsom salts were used for the adjustment.

Puck preparation

The preparation procedure was tightly standardized:

Portafilter preheated to 70°C in a kettle

Basket and shower screen completely dried before every shot

Beans single-dosed

Beans ground frozen

Grinding into a double-walled stainless-steel cup

WDT performed directly in the basket

Home-made WDT tool using three 0.4 mm needles

Decent dosing funnel

0.8 mm “thin” Hog tool moved into and out of the puck

Hog stand used to ensure straight vertical movement

58.5 mm Force Tamper at 33 lb.

These details indicate a deliberate attempt to reduce variation from puck preparation.

TDS measurement

TDS was measured with an Atago PAL refractometer:

Refractometer zeroed with the adjusted Montille water

Coffee samples were not filtered

Measurements made at room temperature

Samples vigorously stirred before measurement

Each reported data point was the average of 3–5 measurements of the same coffee sample.

Intended extraction profile

The extraction-profile slide by Ribes gives the following target assumptions:

Below is the profile used to brew the shots:

The profile shows approximately nine seconds of preinfusion and a predicted total shot time of 34 seconds. Flow initially rises to about 5 mL/s, falls during the low-pressure/bloom stage, and then rises toward 2.6 mL/s. Pressure reaches approximately 2.2 bar during the bloom and then rises to roughly 6.5 bar before gradually declining while flow is held approximately constant.

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4. Proceeding

The experiment proceeded in two principal stages.

First, two 90 g batches of the same coffee were roasted using the Kaffelogic LightSide profile. The first was stopped at 8:24, producing a 10% DTR, while the second roast continued to 8:46, producing a 15% DTR. First crack was recorded for each roast, together with roast-end temperature and subsequent weight loss.

The roast graphs illustrated below show that the overall temperature trajectories were very similar.

In both cases the measured temperature curve tracks the selected LightSide trajectory reasonably closely after the initial turning phase. The actual rate-of-rise curve oscillates around its smoother target but broadly declines as the roast progresses. Power is reduced sharply during the early phase and then progressively increased until the roast is terminated. The second roast largely continues the same general trajectory for longer instead of being produced with a fundamentally different early-roast profile.

First crack was not exactly identical between the batches: Roast 2 cracked six seconds earlier and approximately 1°C cooler. Consequently, the comparison is very close to an “extended development” experiment, but not a perfectly identical roast up to first crack.

Second, espresso was prepared with:

The same grind setting: EK2.6

The same extraction profile

Nominal brew ratio 1:2.6

VST 22 g basket.

The Roast 1 espresso used 19.5 g in and 50 g out.

For Roast 2, the dose was deliberately reduced to 18 g, producing 46 g out, because Ribes adjusted the quantity of coffee to obtain the same extraction pressure.

The resulting brew ratios are identical:

Roast 1: 50 ÷ 19.5 = 2.56

Roast 2: 46 ÷ 18 = 2.56

So the dose changed, but the beverage ratio was effectively held constant.

After extraction, TDS and extraction yield were determined, and the shots were tasted comparatively.

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5. Results

5.1. Roast development

Increasing the target DTR from 10% to 15% changed several physical roast outcomes.

Roast 2 finished:

22 seconds later

3°C hotter

With 1.1 percentage points more weight loss

and had 79 rather than 51 seconds of post-first-crack development.

This is consistent with Roast 2 being meaningfully more developed, even though both were still presented as relatively light/City-style roasts.

The curves are important because they show that this was not a comparison between radically different roasting strategies. The general temperature, power and declining-ROR patterns remained similar. Most of the experimental difference was introduced near and after first crack by allowing the second roast to proceed further.

However, the experiment does not perfectly isolate DTR. First crack itself differed slightly between batches, occurring at 7:33/208°C versus 7:27/207°C.

5.2. Espresso extraction measurements

The central quantitative results were:

Two things are particularly notable.

First, the higher-DTR roast required less coffee to reach the same extraction pressure at the same grind setting and with the same general extraction program. The dose fell from 19.5 g to 18 g, a reduction of approximately 7.7%.

That strongly suggests that roast development altered how the coffee bed behaved hydraulically. In practical terms, less of the 15% DTR coffee was needed to create approximately the same pressure response. This is an inference from the dose adjustment rather than a direct measurement of a material property such as permeability.

Second, the higher-DTR espresso produced lower TDS and lower extraction yield:

TDS declined from 8.9% to 8.6%.

EY declined from 23.1% to 22.1%.

The target specified elsewhere was 8.0–8.5% TDS. Both measured shots therefore exceeded the stated target, although the 15% DTR shot at 8.6% was considerably closer to it.

5.3. Analysis of the actual espresso graphs

The actual shot screens below support the claim that the two shots had closely comparable hydraulic profiles:

Both graphs show a broadly similar blue flow trajectory and green pressure response. Flow initially reaches roughly 5 mL/s, falls sharply in the middle phase, and subsequently rises toward approximately 2.5–2.7 mL/s. Pressure responds with an initial low-pressure phase followed by a later peak and gradual decline.

The approximate maximum pressure is similar in the two plotted shots—visually around the mid-4-bar range—indicating that the dose adjustment did what it was intended to do: bring the two extractions to comparable pressure behavior.

The Roast 1 screenshot additionally records approximately:

4 s preinfusion

36 s pouring

41 s total

2 mL preinfusion volume

100 mL pouring volume

102 mL total machine-estimated volume

50.3 g measured beverage

Temperature goal 95.0°C

Metal temperature 96.0°C.

The Roast 2 display records approximately:

4 s preinfusion

33 s pouring

38 s total

2 mL preinfusion volume

86 mL pouring volume

88 mL total machine-estimated volume

46.3 g beverage

Temperature goal 95.0°C

Metal temperature 93.5°C.

Thus the second shot was approximately three seconds shorter in the recorded actual extraction.

5.4. Sensory results

The strongest result of the experiment was sensory rather than analytical.

According to the presentation, the 15% DTR espresso had:

Significantly increased body

More bitterness

Higher perceived intensity

No unpleasant roast flavors

Less flavor clarity

Lower fruity acidity

compared with the 10% DTR espresso.

This is especially interesting because the 15% DTR shot was perceived as more intense despite having lower TDS: 8.6% versus 8.9%. It also had the lower extraction yield, 22.1% versus 23.1%.

In other words, perceived intensity in this experiment did not simply track the amount of dissolved material in the cup.

Increasing development changed the character of those dissolved compounds—or at least the sensory balance created by them—toward more bitterness and body and away from acidity and clarity.

This is arguably the presentation's most important finding.

The photographs below of the finished cups show both shots with substantial crema. Roast 2 appears somewhat darker in the photograph, but this cannot be regarded as controlled color evidence because cup position, exposure and crema state are not standardized.

5.5. What the measurements do and do not demonstrate

The experimental comparison is useful, but several limitations affect how strongly its conclusions can be generalized.

First, dose was not held constant. Roast 1 used 19.5 g, whereas Roast 2 used 18 g. This was intentional—to match extraction pressure—but means the experiment tests the coffees under a matched-pressure strategy, not under strictly identical dose conditions.

Second, no independent espresso replicates are reported. The protocol states that a data point represents 3–5 measurements of each coffee sample, but these appear to be repeated refractometer measurements of one sample, not 3–5 separately prepared shots.

Third, no blind or randomized sensory protocol is documented. The slides give clear tasting impressions, but there is no information concerning multiple tasters, blindness, tasting order or statistical analysis.

Fourth, the extraction-profile documentation is internally inconsistent, particularly regarding brew temperature, preinfusion time and total shot time.

Fifth, Roast 1 and Roast 2 were not perfectly identical before development. First crack occurred six seconds earlier and 1°C cooler in Roast 2.

The study should therefore be treated as a carefully documented exploratory comparison, rather than a controlled experiment capable of establishing a universal causal law about DTR.

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6. Conclusion

The presentation provides a compact but informative demonstration of how a relatively small change in roast development can materially alter espresso behavior and taste. Extending DTR from 10% to 15% added only 22 seconds to total roast time and 3°C to final temperature, yet it increased weight loss, changed the dose necessary to obtain comparable extraction pressure, and produced a clearly different sensory profile.

Most importantly, the experiment demonstrates that sensory intensity and measured beverage concentration are not the same thing. The more developed coffee produced more body, bitterness and perceived intensity despite its slightly lower TDS and extraction yield.

1: What changes in the roast when Development Time Ratio is increased from 10% to 15% while using the same Kaffelogic “LightSide” profile?

The development phase increased from approximately 51 to 79 seconds. Roast 2 finished 22 seconds later overall, at 218°C rather than 215°C, and its weight loss increased from 12.1% to 13.2%. The underlying curves remained broadly similar, meaning the primary difference was greater late-roast/post-first-crack development rather than a fundamentally different roast trajectory.

2: Does the higher-DTR coffee behave differently during espresso extraction when grind setting and extraction profile are kept the same?

Yes. At the same EK2.6 grind setting and broadly the same extraction strategy, the 15% DTR coffee required the dose to be reduced from 19.5 g to 18 g to obtain approximately the same extraction pressure. This indicates that the coffee's puck/extraction behavior changed with the additional roast development.

3: How do the two roasts differ in objective espresso measurements such as dose, beverage mass, TDS and extraction yield?

Roast 1 produced 50 g espresso from 19.5 g coffee, with 8.9% TDS and 23.1% extraction yield. Roast 2 produced 46 g from 18 g, with 8.6% TDS and 22.1% extraction yield. Both maintained an effective brew ratio of approximately 1:2.56. The higher-DTR coffee therefore produced slightly lower measured concentration and extraction yield under the matched-pressure comparison.

4: What sensory differences result from increasing DTR from 10% to 15%?

The 15% DTR shot had substantially more body, more bitterness and greater perceived intensity. It did not display unpleasant roast flavors, but it had reduced flavor clarity and lower fruity acidity. The 10% DTR shot therefore better preserved the clarity and fruit-acid expression that the extraction profile was intended to emphasize.

5: Can the higher-DTR roast produce greater perceived intensity even if its measured TDS and extraction yield are lower?

Yes. This is exactly what happened here. The 15% DTR espresso was described as more intense even though its TDS fell from 8.9% to 8.6% and its extraction yield from 23.1% to 22.1%. The experiment therefore shows that, within this comparison, sensory intensity was influenced more by the qualitative balance of flavor, bitterness and body than by TDS alone.

Overall, the evidence favors 10% DTR when the priority is floral/fruity character, acidity and flavor clarity, while 15% DTR shifts the same coffee toward body, bitterness and perceived strength without creating obviously unpleasant roast flavors. That final statement should remain specific to this coffee, equipment and procedure because the slides do not supply independent shot replication, blind tasting, or statistical testing.