The 15 bar myth

"15 bar of pressure" is one of the most widespread lines on coffee machine boxes, and one of the most misunderstood. It is not false: that pump really does reach fifteen bar. The point is that the number does not describe the extraction, and whoever reads it thinks it does.

Two different numbers sharing a unit

Maximum pump pressure is how hard the pump pushes against a closed outlet — a component specification, measured without coffee.

Brewing pressure is what establishes itself at the group while water crosses the puck of ground coffee. That is the number that matters, and it is always lower: between pump and group sits an over-pressure valve (OPV) that dumps the excess, and on many machines that valve is calibrated precisely to bring the pump's fifteen bar down to nine at the group.

The two coexist without contradiction, and manufacturers sometimes write it plainly: our catalogue holds official documents that in the same sentence state a 15 bar pump and a 9 bar extraction. Marketing keeps the first half of the sentence and lets the second fall away.

Why nine

Nine bar is neither an arbitrary convention nor a magic number: it is the point at which, with correct grind and dose, water crosses the puck in a time that extracts the desirable compounds without tearing out the bitter ones. More pressure does not extract "more": past a certain point it further compacts the puck and encourages channelling, which is the opposite of what it promises.

It should be said that nine is not dogma either. Machines that profile pressure work deliberately on curves that rise and fall, and there are fine extractions at six or seven bar. But those are choices made knowing what pressure you are working at, which is exactly the opposite of reading fifteen on a box.

What actually makes the difference on inexpensive machines

The real dividing line on an entry-level machine is not the pump: it is the pressurised basket. It is a basket with an extra chamber and a small outlet hole that artificially generates back-pressure. Its purpose is to produce crema even with pre-ground coffee or a wrong grind: the foam is made by the hole, not by the extraction.

It works, and it is meant for people without a grinder. But it makes it nearly impossible to understand what is happening, because the basket masks every error — and masks every improvement too. Moving to a non-pressurised basket is, on many entry-level machines, the single biggest improvement available without changing anything else, provided you have a grinder able to support it.

What our catalogue says

As of 7 September 2026 the portafilter machines declaring a pressure number 17, and the declared values are these: 9 bar on 6 entries, 15 bar on 6, 13 bar on 4, 19 bar on one.

The low count — 17 out of every machine in the catalogue — is no accident and is the most interesting part: most upper-tier manufacturers do not declare a pressure at all, because they know the pump's specification does not describe their product. It is the entry-level segment that puts it on the front page.

Where the value is declared we record it together with the sentence it came from, exactly as the manufacturer wrote it. When that sentence says two things at once — pump and extraction — both remain, and the product page shows which of the two is the data.

What to look at instead of bar

• The pressure gauge, if there is one: it tells you what pressure you are actually brewing at, right now.
• Whether the OPV can be adjusted, which on many machines is a screw and changes everything.
• The basket type: pressurised or not, and it is the only entry on this list you can change for a few euros.
• The grinder. If the grind is wrong, the pressure at the group is decided by the coffee, not by the machine — and no number on a box will change that.