Screening is a mechanical separation process for sorting bulk materials such as gravel or grain by size. Screens are used that are either shaken or rotated to allow smaller pieces to fall through and larger ones to be retained in the screen. This process is also used to separate coffee beans to determine their size and ensure uniform roasting.
The size of coffee beans is a determining factor in their quality. Larger beans tend to be of higher quality, as they mature more slowly and reach a higher density. Sieving coffee is also used to achieve uniform bean sizes and ensure that the beans have a consistent degree of roast when roasted.
Different sieves with different hole sizes are used in coffee sieving. Sieve sizes are usually specified in inches, and the highest quality beans are left in a size 16 sieve. Depending on the growing region, different classifications are used for the coffee screened, with large beans often given designations such as "AA" or "Superior," while medium and small beans are given other designations.
