Single-dose filter basket for the portafilter arm of Rancilio coffee machines.

The filter fits inside the portafilter arm and holds the ground coffee during extraction: pressurised water passes through the filter holes to extract the espresso, while the coffee grounds are retained inside. It is a wear part: over time the holes can clog with coffee residue or limescale, or widen through abrasion, causing extraction that is too fast or too slow, poor crema, or grounds passing through into the cup.

Replace it when extraction becomes irregular, when grounds appear in the cup, or when the filter shows clogged, deformed or corroded holes.