Why we all talk about pressure when making espresso
Anyone who delves deeper into espresso – whether as a passionate home barista or as a technology nerd – will sooner or later stumble upon the same discussion:
"Which pressure is optimal for the perfect cover?"
The internet is teeming with opinions, modifications, and pressure profiles. 9 bar, 6 bar, profiling with slow pre-infusion... but what's this really about?
The Basics: A Classic Espresso Setup
Before we get started, here is the typical parameter framework for a double shot, excluding pressure:
- Basket diameter: approx. 60 mm
- Coffee powder: 15–20 g
- Shot volume: 40–60 ml
- Extraction time: approx. 25 seconds
- Temperature: 90–95 °C
Puckprep vs. grinder setting – what makes the difference?
Once the coffee grounds are perfectly distributed in the sieve and optimally tamped, the only remaining variable for controlling the pressure is the grind size . You can achieve optimal distribution and compression easily and reproducibly with your Barbro vibratory tamper.
The degree of grinding determines how fine or coarse the coffee grounds are – and thus how much resistance they offer to the water flow.
What exactly does the grind size do?
| Coarse ground material | Fine ground material |
|---|---|
| Large particles | Many small particles |
| Small surface area | Large surface |
| Large cavities | Narrow spaces |
| Low bulk density | High bulk density |
| Low pressure loss | High pressure loss |
The pressure loss corresponds to the decrease in static pressure over the height of the puck and is accordingly responsible for the pressure build-up above the puck – and this is where things get exciting.
Pressure loss = resistance = discussion
The pressure in your machine doesn't just happen—it's because the water or pump works against the resistance of the coffee grounds. Without the puck, there would be no increased static pressure in the brewing group.
It follows:
- Coarse grinding → Water flows through the larger cavities more slowly and easier due to the smaller particle surface → lower pressure
- Fine grinding → water flows faster through the smaller cavities and "heavier" due to the larger particle surface → high pressure
But: The pressure is not an active ingredient , but a consequence of the flow resistance .
And what about the extraction?
The speed at which the water flows through the puck affects how quickly flavors are released
- Fine powder → more surface area → faster and more intensive extraction
- Coarse powder → less surface area → milder extraction
Rule of thumb:
Finer powder → higher pressure → higher extraction, with all other conditions remaining the same.
Why does everyone still talk about pressure when espresso is all about taste?
Quite simply: because it can be measured. Pressure can be observed with a manometer, and its changes can be correlated with changes in taste. The degree of grinding can only be determined with great effort using particle size distribution.
Pressure is therefore a practical measurement that can be used to determine flavor development under otherwise constant conditions. The big "pressure debate" is therefore actually a discussion about grind size or extraction . It has been found that, in general, a pressure of 9 bar produces good results.
What else is there to consider?
Extraction during espresso preparation is a so-called batch process that doesn't occur at a constant time. Thus, the static pressure can change under otherwise constant conditions even without active flow profiling, as the particles change their fluidic properties during extraction. Furthermore, the pressure within the puck decreases anyway, which we discussed in our last blog post.