Walk through any espresso machine listing and you will see pressure used as a headline number: 15 bar, 19 bar, 20 bar. The implication is obvious — bigger is better.
It is not. Understanding why is the single fastest way to get better at reading espresso spec sheets.
The number everyone actually agrees on is 9
Espresso, as a brew method, is defined around roughly 9 bar of pressure at the coffee puck. That is the figure commercial machines are built to deliver and the one baristas dial in against. It is not arbitrary — it emerged because it reliably produces the extraction rate, body, and crema that define the drink.
So when a portable machine advertises 20 bar, the honest question is: 20 bar of what, measured where?
Pump rating is not puck pressure
Here is the part that spec sheets rarely explain.
The "20 bar" on most listings is the maximum rated output of the pump — typically measured with no coffee in the path, or as a theoretical peak the pump can reach before it stalls. It is a component specification, not a brewing specification.
By the time water has passed through the group, met the resistance of a packed coffee bed, and exited as espresso, actual pressure at the puck is substantially lower. A pump rated at 20 bar might be delivering something in the 8–10 bar range at the coffee — which is exactly what you want.
In other words: the 20 bar figure and the 9 bar figure are not competing claims. They describe different points in the same system. A machine quoting only the big number is not lying — it is just quoting the number that sounds most impressive rather than the one that predicts what is in your cup.
Why more pressure is not better
Suppose you could actually force 20 bar through the puck. You would not get better espresso. You would get:
- Channelling. Excess pressure fractures the coffee bed, opening low-resistance routes that water rushes through, bypassing most of the grounds.
- Harsh, over-extracted flavour from the parts of the bed that do get saturated.
- Thin body, because a fractured puck cannot build the even resistance that produces proper crema.
This is why commercial machines do not chase higher numbers. The industry settled on ~9 bar because that is where the drink is best, not because it was the most they could manage.
What actually matters: stability
Here is the spec nobody advertises, and the one that separates a good shot from a bad one — can the machine hold its pressure for the whole extraction?
A shot takes roughly 25–30 seconds. Over that window, a small battery-powered pump has to fight a rising back-pressure as the puck saturates. Many portable machines cannot. They spike at the start, sag through the middle, and trail off at the end. That is the real cause of the thin, watery shots people blame on their beans.
This is why Cera+ quotes the Ceramax as delivering a stable 9 bar extraction with up to 20 bar peak performance — two numbers, describing two different things, both stated honestly. The 9 bar figure is the one that determines your shot. The 20 bar figure describes the headroom the pump has to hold that 9 bar steady when the puck fights back.
How to read a pressure claim
A quick checklist for any machine you are evaluating:
- Does it state a working pressure, or only a maximum? A single big number with no context is a marketing figure.
- Does it mention stability or hold time? Peak pressure over 3 seconds is not the same as steady pressure over 30.
- Is there a pre-infusion stage? Gently wetting the puck before full pressure reduces channelling significantly — and it requires real pressure control, not just a strong pump.
- Is the basket standard size? Pressure behaves differently across a wide bed than a narrow one. (We covered this in the 58mm article.)
Where control beats raw power
If pressure stability is what matters, then the useful feature is not a bigger pump — it is the ability to manage the extraction. On the Ceramax that means pre-infusion, adjustable temperature (84 / 88 / 92 / 96°C), and adjustable extraction time, all set from the Cera+ app and saved so you can repeat the shot that worked.
That is a meaningfully different design goal from "make the number on the box bigger."
The short version
9 bar is the target. 20 bar is the headroom. A machine that only tells you the second number is telling you about its pump, not about your coffee. Ask what it holds, for how long — that is the spec that reaches your cup.
Next in the Brew Guide: how to dial in a shot when you did not bring a scale.
