Pressure Profiling Simulator (Espresso)
Pressure is the invisible lever in espresso
You can't see it, but it shapes the shot: how gently the water first wets the puck, how high the pressure rises and how it tails off. Play through what pre-infusion, peak pressure and profile change in the model — and when the water starts looking for channels.
The controls: profile (declining, flat, rising), pre-infusion on or off, peak pressure in bar (4–12), grind size as a relative scale.
The results: EstimateModel values, not measurements; the curve shows the course of the shot, not seconds. The basis: the 9-bar convention, a sensory study on pressure and recent measurements of pressure and flow. No guarantee — details right below the tool.
In more detail: controls, model and sources
The controls in detail: Pre-infusion is a switch, on or off — in the model, 2.5 bar for the first fifth of the shot. Peak pressure has a real unit: 4 to 12 bar in steps of 0.5 bar. Profile offers three shapes — declining, flat, rising. Good to know: in the calculation, this choice changes only two results, namely clarity / sweetness and bitterness. Flow, crema, dissolved amount and channeling risk are unaffected by it. Grind size is a relative scale from 0 to 100 without a unit: 0 is coarse, 100 is very fine. These are not micrometres and not the marks on your grinder — the number only describes how much resistance the coffee bed offers the water.
The results in detail: Channeling risk, dissolved amount (extraction), crema, clarity / sweetness and bitterness are indicators from 0 to 100, not measurements and not lab results. They show you the direction your shot is moving in, not how it will taste. “Evenness” isn't a separate value here but simply 100 minus channeling risk — the same number seen from the other side; that's why we no longer show it as its own bar. The curve “pressure in bar over the shot” is calculated too: it shows what your control setting produces in the model — a calculated value, not a measurement on your machine. Its horizontal axis is the course from start to finish, deliberately without seconds: we don't brew by the clock, and a number on this axis would quickly be misread as a target.
The basis in detail: The 9 bar come from the Italian definition of espresso (INEI) — a convention, not a proven optimum. Peer-reviewedThat pressure shifts taste is shown by the sensory study of Andueza et al. 2002 (J. Agric. Food Chem. 50, 7426–7431): at 11 bar the espresso became bitter and astringent, at 7 bar the foam was unstable, at 9 bar foam consistency and fruity aroma compounds were best — at a fixed grind size. That's what the model's bitterness above 9 bar and the crema are based on. That more pressure does not mean more flow was measured by Waszkiewicz et al. 2026 (Physics of Fluids 38, 063113, University of Warsaw) on 60 shots between 1 and 12 bar: flow reaches a maximum around 5 bar; above that, the puck compresses and flow drops again. The model therefore uses a flow factor that rises up to 5 bar and falls slightly above it — the direction is measured, the strength of the drop is our assumption. That the water front needs 5 to 10 seconds to penetrate the puck and displace the air is shown by the flow and mass curves of the same paper (Waszkiewicz et al. 2026; the wetting itself was filmed time-resolved by Foster et al. 2025, Physics of Fluids 37, 013383); that's why the animation starts with a wetting phase. AssumptionThat pre-infusion reduces channeling is plausible and claimed by every manufacturer — it has not been measured. Cameron et al. 2020 (Matter 2, 631–648) show what uneven flow costs (at the finest grind size, the measured yield was up to 13.1 % below what the model predicted — the authors explain this with clumping and uneven flow), not that pre-infusion prevents channels; their model explicitly applies only after wetting. The calculation here still lowers the channeling risk noticeably with pre-infusion — as an experience value, not a measurement. That a declining profile takes out bitterness is likewise an experience value from practice with lever machines, not a study. ManufacturerPre-infusion values in practice: La Marzocco 3 bar or line pressure, 2–8 s; Slayer from 0.5 bar, typically 2.5 bar; Decent from pressureless up to around 6.8 bar depending on the profile — manufacturer figures, not re-measured by us. More on this on our page about the chemistry of pre-infusion.
A contradiction we named openly — and resolved in October 2026: The old version of this tool calculated flow proportional to pressure (9 bar as the 100 percent reference) and rated only 8 to 10 bar as “in the window”; the text next to it played down the 9 bar as tradition. Anyone who set the control to 6 or 7 bar got a harsher verdict than the data supports — many people today deliberately work at 6 to 7 bar and are very happy with it; Cameron et al. 2020 brewed their experiments at 6 bar. We've corrected both: flow now follows the measurement by Waszkiewicz et al. 2026, and the tool only puts the pressure in context (low, usual, high) instead of rating it. We'd rather say this clearly than quietly replace the old calculation logic.
The Pressure Profiling Simulator is loading … If nothing appears, please reload the page — or have a look at espresso machines.
This is a simulator. It works with a simplified model and shows you relationships — not measurements and not an assurance of any kind. What ends up in your cup depends on your machine, your water, your beans and the way you work.
Our recommendations are based on experience from consultations, courses and the showroom. They are non-binding and provided without guarantee. We accept no liability for damage arising from their use. When in doubt, what your manufacturer writes in the instruction manual applies.
Straight to the results: The five bar values are indicators from 0 to 100 from our model — not measurements. The bar values in the curve are also a calculated value from the model and not a measurement on your machine: the curve draws what your control produces in the model — not what is actually present in your group head.
Pre-infusion, peak pressure and profile
Pressure drives the water through the coffee puck. How fast depends on the resistance of the coffee bed (finer grind = more resistance) — and not simply on how high the pressure is: measurements on 60 shots show that flow reaches its maximum around 5 bar and drops again at higher pressure because the puck compresses (Waszkiewicz et al. 2026). A pre-infusion — brief pre-wetting at low pressure — wets the puck before full pressure arrives; the water front needs 5 to 10 seconds for this (Waszkiewicz et al. 2026). That this reduces channels (channeling), through which water shoots unevenly and over-extracts one part of the coffee while under-extracting another, is plausible and widespread practice — it hasn't been measured so far.
The peak pressure shapes crema and taste. The Italian espresso standard is 9 bar ± 1 — a tradition from the spring lever machine, not a physically proven optimum, but not arbitrary either: Andueza et al. 2002 compared 7, 9 and 11 bar. At 11 bar the espresso became bitter and astringent, at 7 bar the foam was unstable, at 9 bar foam and fruity aromas were best — at a fixed grind size. A declining profile (start high, tail off gently) — as classic lever machines deliver by nature — in our experience often takes out bitterness towards the end; we're not aware of a study on it.
The Italian association INEI describes certified espresso with five numbers. We've checked them, and they're correct: dose 7 g ± 0.5, water temperature at the group head outlet 88 °C ± 2, pressure 9 bar ± 1, flow time 25 s ± 5 and 25 ml ± 2.5 in the cup, crema included (plus 67 °C ± 3 drinking temperature). That's a product definition, not a law of nature: it defines what may be called “espresso” in Italy — not what tastes best. For us, the 25 seconds in it are an observation, not a target.
Correction, stated openly: Until October 2026, the simulator above normalised flow to a fixed 9 bar and called only 8 to 10 bar “in the window” — a harsher verdict on 6 or 7 bar than is justified. We've adapted the calculation logic to the measurements (flow maximum around 5 bar) and replaced the verdict with a classification. The details are in the expandable note above the tool.
Important in the CCC sense: pressure is a tool, not an end in itself. We choose by taste, weight and ratio — not by the clock. There's no right or wrong; the cup decides.
Sources: Istituto Nazionale Espresso Italiano (certified Italian espresso: 7 g ± 0.5, 88 °C ± 2 at the group outlet, 9 bar ± 1, 25 s ± 5, 25 ml ± 2.5 including crema — checked by us); Andueza, S. et al. (2002), “Influence of water pressure on the final quality of Arabica espresso coffee”, J. Agric. Food Chem. 50(25), 7426–7431, doi:10.1021/jf0206623; Waszkiewicz, R. et al. (2026), “Under pressure: poroelastic regulation of flow in espresso brewing”, Physics of Fluids 38, 063113, doi:10.1063/5.0319611 (60 shots, 1–12 bar: flow maximum around 5 bar; water front 5–10 s); Foster, J. M. et al. (2025), “Dynamics of liquid infiltration into an espresso bed using time-resolved micro-computed tomography”, Physics of Fluids 37, 013383, doi:10.1063/5.0245167 (wetting of the puck filmed); Cameron, M. I. et al. (2020), “Systematically Improving Espresso”, Matter 2(3), 631–648 (extraction evenness & channel formation, brewed at 6 bar).
Controlling pressure
Whether pre-infusion, pressure profile or classic 9 bar — how much control you have depends on the machine. A good fit if you want to feel the pressure by hand: on a Flair lever machine, you build the profile yourself. A good fit if the machine should store the profile: paddle and profiling models such as those from La Marzocco control pressure and flow electronically. You'll find the overview of all espresso machines here. How pressure interacts with grind size and ratio is shown in the Extraction Simulator; an even puck starts in the Puck Prep Workshop. Questions about your setup are answered by Jackson, our AI advisor, around the clock.
Frequently asked questions
What does pressure profiling mean in espresso?
Pressure profiling means deliberately changing the pressure over the course of the extraction instead of keeping it constant — for example with a pre-infusion at low pressure, a peak pressure and a declining tail. This lets you influence evenness, crema and taste.
How many bar does an espresso need?
The Italian standard (INEI) is 9 bar ± 1. That's a tradition from the spring lever machine, not a physically proven optimum — but not arbitrary either: in a sensory study (Andueza et al. 2002), espresso tasted bitter and astringent at 11 bar, and at 7 bar the foam was unstable. Many people deliberately work at 6 to 7 bar; Cameron et al. 2020 brewed at 6 bar. What matters is the taste in the cup. The simulator above puts the pressure in context (low, usual, high) and doesn't rate it.
What does pre-infusion do?
A pre-infusion wets the puck at low pressure before full pressure arrives; the water front needs 5 to 10 seconds for this. That this reduces channels and makes extraction more even is plausible and widespread practice — especially with lighter roasts — but not supported by a controlled study.
Does higher pressure mean more extraction?
Not automatically. More pressure doesn't even mean more flow: the puck compresses, and above around 5 bar the flow drops again (Waszkiewicz et al. 2026). Too much pressure can encourage channels that extract unevenly. More pressure means more crema, but not necessarily better taste — weight, ratio and taste decide.
You'll find all interactive tools bundled in our Coffee Tools.
