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.

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