What is foreign matter in green coffee grading?

Foreign matter refers to any non-coffee material present in a lot of green coffee - sticks, stones, soil, leaves, husks, insect debris, or other extraneous material that has entered the batch during harvesting, processing, or storage. Its presence is recorded as a defect category in green coffee grading and contributes to the defect count that determines whether a lot meets specialty grade standards.

In the SCA green grading system, foreign matter is classified as a primary defect: a single piece of foreign matter in a 350g sample counts as a full primary defect. Specialty grade requires zero primary defects in the sample, meaning any detectable foreign matter disqualifies a lot from the 80+ point specialty designation regardless of cup quality.

Foreign matter enters the supply chain at multiple points. At harvest, leaves and small branches are picked alongside cherry in strip-picking operations. During drying, wind can carry material onto patios or raised beds. During milling, stones or soil may be introduced from machinery or storage surfaces. Most dry mills operate colour sorters, density separators, and in some cases X-ray equipment specifically to detect and remove foreign matter before export. For buyers, the presence of foreign matter in a green sample - even small amounts - is worth flagging as it suggests quality control gaps at the dry mill.