What's the Difference Between AA and AB Grade Coffee? What Are the Three Main Grading Systems for Coffee Beans? What Are the Characteristics of Kenyan Coffee?

Observant coffee lovers will have noticed that most coffee beans sold by merchants carry an "AA" suffix. The most common examples are Kenyan coffees: Kenya Nyeri AA, Kenya Kirimiri AA, and so on.

It is not just Kenya. Beans from Tanzania, Uganda, and other countries carry the same AA suffix. Which raises the question: what does AA mean, and why do beans from these countries all emphasize AA?

What Does the AA Suffix on Coffee Beans Mean?

The "AA" suffix on a coffee bean actually represents its grade. Coffee beans are not industrial products, so their quality varies, and a system is needed to distinguish better beans from lesser ones. That system is grading. So when we see beans from a certain country followed by the letters AA, we know that country's grading method is based on size.

Understanding Coffee Bean Grading Systems

Two points are worth clarifying here. First, coffee grading systems are not only based on size; there are other methods based on defects and altitude, and how they are applied depends on each country's conditions, which FrontStreet Coffee will cover in detail another time. Second, not every size-based grading system uses uppercase English letters as identifiers, because identifiers like AA and AB are unit systems developed by the British. Most producing countries use them because they were formerly under British colonial rule. Colombia, for example, also grades beans by size, but its grade identifiers are terms such as Supremo and Excelso.

Kenya's Size-Based Grading System

The most famous producing region using size-based grading is ultimately Kenya, because the Kenyan government takes the coffee industry extremely seriously and sets very strict requirements for quality. Here is how Kenya's size-based grading system works.

AA: Bean size between 17-18 screen.

AB: Bean size between 15-16 screen.

C: C-grade beans have a screen size between 12-14. Because of their small size, this grade is generally not classified as specialty grade.

PB: Rare round-shaped green beans, abbreviated as peaberries.

E: Full name Elephant, meaning elephant beans. Note that "elephant beans" here does not refer to the elephant bean varieties in coffee species, Maragogipe and Pacamara, but to special beans with abnormal development, like peaberries. These form when two coffee beans become entangled during development into what looks like a very large, swollen bean. They exceed 18 screen size and are extremely rare.

TT: TT grade consists of lightweight beans blown out by air classifiers from AA and AB grade beans.

T: T grade consists of lightweight beans blown out by air classifiers from C grade beans.

MH/ML: These two grades are of lower quality, so they are not processed using Kenyan-style washing. They are generally for domestic consumption and do not circulate outside Kenya.

That is Kenya's national official grading system, and it shows that AA represents the highest grade in Kenya, meaning the best. Recently, however, FrontStreet Coffee shared a review article, "Does Coffee Bean Flavor Quality Relate to Size?", which detailed the shortcomings of size-based grading: it has too many loopholes, because bean size does not directly affect flavor quality.

Coffee professionals often use this example: plant the same variety at 900 meters and at 1700 meters. Even if the harvested beans are the same size, the 900-meter coffee will definitely not taste as good as the coffee grown at 1700 meters, because the growing environment is one of the main factors shaping flavor as the bean develops.

Evolution of Coffee Grading Systems

In an era when bigger was better, such grading systems were naturally mainstream, and the old-school producing countries basically adopted size-based grading. When the concept of specialty coffee emerged, people became aware of the key factors behind flavor formation, giving birth to entirely new grading systems. Kenya did not fall behind either: local coffee research institutions and green coffee traders use their own custom methods to conduct secondary grading of AA and AB Kenyan coffees.

That system is called the Coffee Bean Quality Grading Procedure, or Kenyan Classification Procedure by Quality Assessment, and it was established by the Kenyan Coffee Research Foundation. It comprehensively evaluates beans on three aspects: green bean quality, roasted bean quality, and cupping quality.

Secondary Grading Markers

TOP, Plus (+), and FAQ are secondary grading markers. When beans receive the corresponding grade scores, these markers are added to the original grade, such as Kenya AA TOP or Kenya AA+. They indicate beans that perform outstandingly within the AA or AB grades, while FAQ represents beans with slight defects that do not affect flavor.

Finally, note that because this system is not officially certified by Kenya, most Kenyan beans on the market are still ranked mainly by conventional size grading, that is, AA and AB.

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FrontStreet Coffee Recommendation

Grading tells you about bean size, but it says little about flavor, which is why Colombia uses its own Supremo and Excelso terms rather than the British system. FrontStreet Colombia Washed Huila comes from Huila in the southern part of Colombia's central mountain range, the country's best-known specialty region, surrounded by hills and planted above 1500 meters where the country's most important rivers converge. Roasted medium-dark, it brings out dark chocolate and nutty sweetness with moderate oils and a full body, and it works for pour-over and French press as well as moka pot and espresso machine.

Colombian coffee also shows how processing can reshape flavor. FrontStreet Colombia Frontera Estate Sidra uses anaerobic natural processing, fermenting in a low-oxygen or oxygen-free environment to develop more tropical fruit aromas; at a medium-light roast it yields complex, intense notes of passionfruit, grape, apricot, and dried fruit. And for anyone with a home espresso machine or moka pot, FrontStreet Specialty Blend combines the creamy nuttiness of Brazilian coffee with the dark chocolate bittersweetness of Colombian coffee, pulling with a fine golden crema and making a rich, smooth latte.