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.

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