The silverskin is a thin membrane around each bean. During roasting, it detaches as chaff and is extracted by the roaster's ventilation. Residue in the grinder or portafilter is normal and harmless.

What happens to the silverskin of the coffee bean during roasting?

The silverskin is a thin membrane around each bean. During roasting, it detaches as chaff and is extracted by the roaster’s ventilation. Residue in the grinder or portafilter is normal and harmless.

Why that matters

Every coffee bean is surrounded by a paper-thin layer called the silverskin (or silver skin). It’s the innermost layer of the coffee cherry — what remains after all the outer layers have been removed during processing. On green (unroasted) beans, the silverskin is clearly visible as a light, silvery film, particularly in the centre crease of the bean.

During roasting, the bean expands by 50–100% in volume. The silverskin can’t keep up with this expansion and detaches in thin, papery flakes — known as chaff. Commercial drum roasters have built-in ventilation systems that suction this chaff away during the roast. In home roasting, chaff is one of the messier aspects of the process.

The amount of chaff varies by processing method. Washed coffees tend to have less residual silverskin because the fermentation and washing steps remove most of it. Natural and honey-processed coffees often retain more silverskin, producing more chaff during roasting.

Silverskin itself is flavour-neutral to slightly papery. Small amounts left on the bean after roasting don’t affect taste. However, excessive chaff in a grinder can clog burrs over time, which is why regular cleaning matters. In espresso machines, tiny flakes occasionally appear in the portafilter — purely cosmetic, not a quality issue.

At Green Wall Coffee

At Sophienstraße 27 in Berlin-Lichtenberg, guests sometimes notice fine flakes in their ground coffee or on the counter after grinding. I explain: that’s silverskin, and it’s completely normal. It’s a sign that the coffee was roasted relatively recently — on older coffee, any remaining silverskin has usually disintegrated.

Related Questions

• Why does coffee need to be roasted?
• What is first crack and second crack?
• Why do coffee beans crack during roasting?

More depth on this topic in the article How to Make Perfect Espresso. Or stop by at Sophienstraße 27 — Mon–Fri 8am–5pm, Sat 10am–5pm.