What is a coffee screen size?

Before coffee beans ever reach a roaster, they undergo a sorting process that determines their future. One of the most important metrics in this phase is screen size. Imagine a series of stacked metal sieves with holes of specific diameters, measured in 1/64th of an inch. Screen size 18, for example, means the beans are 18/64ths of an inch in diameter. This systematic sizing is a cornerstone of the global coffee trade.

Why does size matter? In many cases, size is used as an indicator of quality. Generally, larger beans are perceived to be denser and contain more concentrated sugars and nutrients, which can translate into a more complex flavor in the cup. However, this isn't a hard-and-fast rule; smaller beans, such as peaberries or those from specific high-altitude varietals, can be exceptionally delicious. The primary benefit of sorting by screen size is physical consistency.

When a lot of coffee has a uniform screen size, the roaster has a much easier time applying heat evenly. If a bag contains a mix of tiny, medium, and large beans, the smaller ones will roast faster and potentially burn, while the larger ones might remain underdeveloped. By separating the beans, producers can offer roasters a product that behaves predictably in the drum, leading to a much more balanced and clean-tasting coffee.

For the reader, you will often see these screen sizes translated into common commercial grades like "AA" or "AB," particularly in regions like Kenya. While these grades are helpful shorthand for buyers, they are just one part of the picture. A high screen size does not automatically guarantee a high cupping score, but it is a reliable sign that the producer has taken the time to sort and process their harvest with care.