What is a pressurised basket?

Look at the underside of your filter basket. If it is covered in dozens of small holes, it is a normal (single-wall) basket. If it has one small hole in an otherwise solid plate — often behind a removable outer shell — it is pressurised.

How it works

In a normal basket, resistance comes from the coffee itself. Water at nine bars has to push through a compacted bed, and how fast it does that depends on your grind, your dose and your distribution.

In a pressurised basket, the coffee bed is nearly irrelevant. Water passes through it easily, then meets the single small hole, and pressure builds against that valve instead. The coffee emerges through the hole as an aerated stream with a foamy head that looks like crema.

Why manufacturers fit them

Forgiveness. A machine with pressurised baskets works on day one with supermarket pre-ground coffee and no grinder. It produces something recognisably espresso-shaped from almost any input, which is exactly what an entry-level buyer needs.

Why they cap you

Because pressure no longer comes from the coffee, the variables that make espresso interesting stop mattering. Grinding finer barely changes the cup. Distribution barely changes the cup. The foam is manufactured by a valve rather than emulsified by pressure through the puck, so it collapses faster and tells you nothing.

You cannot improve, because there is nothing to adjust.

Switching to a normal basket

Worth doing — but only once you own a grinder that goes fine enough and holds consistency. Fitting a non-pressurised basket without one gives sour, gushing shots and a machine that is worse than it was.

Order of operations: grinder first, basket second.