What is screening in coffee processing?

Screening is the process of sorting green coffee beans by size using perforated metal screens with holes of a fixed diameter. It's a standard step in dry milling, creating lots of consistent bean size for both quality and roasting purposes.

In practice, coffee passes over a series of screens with progressively different hole sizes. Beans too large to fall through a given screen are retained on it; smaller beans fall through to the next. This stratifies the batch into size categories that can be designated as specific grades or blended to a specification.

Screening directly affects roasting consistency - a uniform screen-size lot develops more evenly in the drum. It also makes grading designations meaningful to buyers: a screen 15+ lot tells you exactly what size range to expect. Screening is usually combined with density sorting and colour sorting as part of a comprehensive dry milling preparation process.