Looking at the Benchmark list of green coffees is like singing the Jackson five-song ABC. The letters AA, C, PB, PSC AX, and Y are situated next to the coffee farm name. It looks like some secret code, but these letters provide useful information for green coffee traders, roasters, and green buyers: They are the “grade” of the coffee. Green coffee grading systems are different in different countries (and some don’t use letters at all), however, grades are widely used throughout the industry for simple quality identification and contract fulfillment. The grading system for coffees first came about for commodity and commercial contracts which treat beans as relating to a grade or class. For example, all AA graded beans from an origin are relatively uniform in size. Unlike specialty coffees that emphasize who the producers are, the micro-region, processing methods, and cupping score, in the commodity world, the grade tells the whole story.
Size is the primary way coffee is graded throughout the coffee industry. Once the coffee is free from its parchment layer (the outer shell), it gets sorted by vibrating screens with different sized slotted holes which allow the unroasted coffee beans to fall wherever they fit. Each screen, with their respective slotted holes, is associated with a different grade. The largest hole is 20/64 of an inch and the smallest is 8/64 of an inch. Typically, specialty coffee is 14/64 and above.
In countries like Kenya and Colombia, the bigger the bean, the better. In Kenya, the largest beans are AA, while in Colombia, their grading system identifies the largest beans as Supremo. The general thinking is that larger beans are superior because they grow at higher altitudes. At higher altitudes, coffees mature more slowly due to the colder temperatures. This longer maturation process creates deeper, richer flavors. This longer maturation process also often (but not always) allows the beans to grow larger than lower altitude coffees. While size is a primary way of examining a coffees quality, it is not always accurate and is not the only way of grading coffee. Ethiopian coffees, for instance, often fall well under the AA size standard. Though small, most Ethiopian coffee grows between 1500 and 2000 meters above sea level (MASL), which is quite high. The beans mature slowly, have great density, taste extraordinary, and have an average screen size of 14/64. These tiny coffee beans are just as good, and sometimes better than their larger bean counterparts.
In Ethiopia, cleanliness is next to godliness and it is the preferred measurement of quality. This cleanliness refers to the amount of defects found in the beans. These defects can include insect damage, milling damage, sticks, stones, and foreign matter. Here, coffee gets graded by the number of defects, with grades ranging from 1 to 9: The least amount of defects receives the highest the grade.
In other places such as Central America, the harder the bean, the better. They grade the coffee based on elevation, with Strictly Hard Bean (SHB) being their highest grade. For beans to be SHB, they must grow at 1,600–1,700 meters above sea level.
Papua New Guinea follows the size grading system, like in Kenya. They also measure the bean shape, color, cup quality, and presence of defects. Grades include AA, A, B, C, PB, PSC AX, and Y. AA is 18/64 which is the largest generally available bean for the origin. While AA is the largest, we often see lower grades being selected in blind cuppings. In the end of the day, grading systems help systematize the classification of different coffees for quality identification, but they are fragmented and imperfect systems. Like many large systems, they also grossly simplify the reality. While grades give a baseline understanding of quality for contracting purposes at larger scales, the only true way to know what you’re getting is to taste the coffee and know your source!