What is chaff in coffee roasting?

Chaff is the thin, papery skin that detaches from coffee beans during roasting. It's the silverskin - the innermost seed coat that clings to the bean after processing - which becomes brittle and separates as the bean expands and the cellular structure changes under heat.

In a drum roaster, chaff is collected in a chaff collector or cyclone - a separate chamber where the lightweight flakes are captured as airflow carries them away from the drum. Managing chaff is both a practical and a safety consideration: accumulated chaff is a combustion risk in an enclosed roasting environment, and most dedicated home roasters include a chaff collection system for this reason. Popcorn popper roasters produce large amounts of chaff that need to be managed during the roast itself.

The amount of chaff varies by coffee. Naturals tend to produce more than washed coffees, and certain origins - Ethiopian naturals in particular - are notably chaff-heavy. A significant chaff deposit after a roast is a normal result, not a sign of a problem. Emptying the chaff collector between roasts is simply good maintenance practice, both for consistency and safety.