What is "screen 18"?

In the coffee industry, "screen size" is a standard method for measuring the physical dimensions of green coffee beans. The term "screen 18" specifically means that the beans have been passed through a grading screen with holes that are 18/64ths of an inch in diameter. Beans that are retained on this screen are considered large, which is often associated with higher quality and maturity in many coffee-growing regions.

The process of screen sizing is essential for achieving uniformity. When a lot of coffee is sorted by size, the beans are more likely to have similar density and moisture content. This is crucial for the roaster, as uniform beans will absorb heat at a similar rate. If a lot contains a mix of very large and very small beans, the smaller ones might roast too quickly, leading to burnt or bitter flavors, while the larger ones might remain under-developed. By selecting for a specific screen size like 18, producers can offer a more consistent product.

It is important to note that while screen size is a useful indicator of quality, it is not the only one. A large bean does not automatically guarantee a better flavor. Factors like the coffee variety, the altitude at which it was grown, and the processing method are equally, if not more, important. However, in many markets, larger beans are preferred for their aesthetic appeal and the perception that they represent the best of the harvest.

For the consumer, seeing "screen 18" on a bag of coffee is a sign that the lot has been carefully sorted. It tells you that the producer has invested in the equipment and labor necessary to ensure that the beans are uniform. This attention to detail is a hallmark of specialty coffee, where every step of the process is designed to enhance the final cup.

In practice, screen 18 is a benchmark for quality. It is a simple, objective measurement that helps roasters and traders communicate about the physical characteristics of a coffee. When you brew a coffee that is consistently screen 18, you can expect a more predictable and balanced experience, as the beans have been selected for their size and, by extension, their potential for even roasting.