Classification by Screen Size
After milling, Kenyan coffee is graded primarily by bean size, with the assumption that larger beans tend to have a more developed flavor. The main screen size classifications based on the Kenyan Department of Agriculture, Coffee Directorate and the Nairobi Coffee Exchange are:
AA: Beans that pass through a screen size of 18 and are retained by a screen size of 17. This is the largest and most visually impressive grade. (screen size 18)
AB: A mix of A and B beans (screen sizes 16/17). AB is the most common grade and often delivers excellent quality.
PB (Peaberries): A natural mutation where only one bean develops inside the cherry rather than two. Peaberries are smaller (screen size 12+) and rounder, often prized for their dense, vibrant cup profiles.
C, E, TT, T, UG: Other grades that include smaller beans (C), larger screen outliers (E), lighter or broken beans (TT, T), or lower quality/ungraded coffee (UG).
Grades of AA, AB, PB only allow for a maximum of 5% above or below of indicated size of screen.