What is 'screen sorting'?
Screen sorting is a mechanical grading process where green coffee beans are passed through a series of metal screens with holes of standardized diameters. This method separates beans by size, which is a key indicator of quality and density. By ensuring uniform bean sizing, producers can achieve more consistent roasting results and remove smaller, lower-quality beans from the final lot.
Screen sorting is one of the most fundamental steps in the post-harvest journey of coffee. After the beans have been hulled and cleaned, they are often a mix of different sizes. Because larger beans are generally denser and have developed more slowly at higher altitudes, they are often perceived as higher quality. Screen sorting allows producers to separate these beans, creating lots that are uniform in size and, by extension, more predictable in the roaster.
The process is simple but effective: the beans are shaken over a stack of metal screens, each with holes of a specific size, measured in 1/64th of an inch. A Screen 18, for example, has holes 18/64 of an inch in diameter. Beans that are larger than the holes are retained on the screen, while smaller beans fall through to the next level. This allows the mill to categorize the coffee into specific grades, such as 'AA' or 'Supremo,' which are essentially shorthand for the size of the beans.
For the roaster, this uniformity is a gift. When a batch of coffee is uniform in size, it absorbs heat evenly. If you were to roast a mix of tiny and large beans, the small ones would likely burn before the large ones were fully developed. By using screen sorting, the producer ensures that the roaster can create a consistent, balanced profile that highlights the best characteristics of the coffee.
In practice, screen sorting is a hallmark of quality control. While it doesn't tell you everything about the flavor—a large bean can still be a bad bean if it was processed poorly—it is a vital step in the professionalization of the coffee supply chain. When you buy a bag of specialty coffee, you are benefiting from this mechanical precision, which ensures that the coffee you brew is as consistent and delicious as the roaster intended.
- · https://achillescoffeeroasters.com/blogs/specialty-coffee-blog/how-coffee-is-graded-scores-defects-bean-size-quality-and-specialty-coffee-standards
- · https://agriculture.institute/post-harvest-mgt-value-addition/coffee-grading-techniques-quality-assessment
- · https://www.greenplantation.com/a/coffee-bean-size-how-is-the-coffee-graded-and-what-is-the-quality-of-the-coffee