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.
2. Questions asked
The experiment can be organized around five principal questions:
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:
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!"
Step 1 – Preinfusion
Thus, the 20-second value acted as a maximum rather than necessarily determining the actual preinfusion duration.
Step 2 – Low-pressure bloom
This created a pressurized blooming period after initial saturation.
Step 3 – Flow rise
Rather than abruptly imposing the extraction flow, the machine gradually increased flow to the final target.
Step 4 – Hold flow
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:
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:
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:
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:
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:
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:
Peak pressure was approximately 7.2 bar, much closer to Shot 1.
The critical comparison was then between:
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.
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:
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:
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:
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:
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:
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.
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?
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?
3. Does changing from the IMS CI 200 IM to the IMS SI 200 IM produce a noticeable difference in taste?
4. Does the IMS SI 200 IM change the physical condition and behavior of the coffee puck after extraction?
5. Does the IMS SI 200 IM improve the radial uniformity of extraction between the center, middle, and outer regions of the puck?
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.
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mirjam created 2026/08/27, mirjam updated 2026/10/07