Screen Size

In the global coffee trade, screen size is frequently misunderstood as a proxy for quality, leading to the persistent myth that larger beans are inherently superior. In reality, screen size is a mechanical tool for standardization. At the dry mill, coffee is passed over vibrating tables equipped with perforated screens. A 'Screen 18' bean, for instance, is retained by a sieve with 18/64-inch holes, while smaller beans fall through. This process allows producers to create uniform lots that meet specific export contracts, such as Kenya’s AA or Colombia’s Supremo. For the producer, this is a matter of logistics and market access; different botanical varieties naturally produce different bean sizes, and sorting ensures that a lot behaves consistently during the roasting process. When beans of vastly different sizes are roasted together, the smaller beans may reach the desired roast degree significantly faster than the larger ones, leading to uneven development and potential defects in the final cup. By separating beans by size, mills provide roasters with a predictable raw material. While high-altitude environments can sometimes correlate with larger, denser beans, size remains a physical attribute. A smaller bean from a high-quality variety, processed with care, will consistently outperform a large bean from a lower-quality variety. The grading system is a language of trade, not a definitive indicator of flavor.