How Kenyan Coffee Beans Are Graded and Classified

When you buy a bag labeled 'Kenya AA,' have you ever wondered how those beans earned that grade? Unlike origin flavor notes, coffee grading is a physical process based on bean size, weight, and density — and Kenya’s system is one of the most structured in the world. This article explains exactly how Kenyan coffee beans are sorted, why some earn top grades like AA or PB, and what the rest of the letters really mean.

Kenyan coffee beans are classified into lettered grades primarily by screen size (mesh), with AA being 17–18 mesh, AB 15–16 mesh, and E for extra-large beans (18 mesh and up), including peaberries. Other grades include PB (peaberry), T (low-grade small beans), and C (light or defective). Ungraded beans are marked UG1 or UG2. Natural processed beans are further split into high-quality Heavy Mbuni (MH) and lower-grade Light Mbuni (ML).

How Kenyan Coffee Gets Its Grade

After harvest, Kenyan coffee cherries are handpicked, sorted to remove unripe or overripe fruit, pulped, fermented for around 36 hours, then dried on raised beds. Once dry, the beans (now called parchment coffee) are milled to remove the husk. Only then do they enter the strict grading process based on physical traits.

The Grading System: Mesh Size and Quality

Kenya uses a screen-sizing system measured in mesh numbers to sort green beans by diameter. Here’s how it breaks down:

• E Grade: 18 mesh and above (includes peaberries), the largest beans available; also includes large round beans. Relatively rare.
• AA Grade: 17–18 mesh. This is the top commercial grade in Kenya, often considered the highest quality for export. These are large, dense beans with high potential cup quality.
• AB Grade: 15–16 mesh. A mix of A (16+ mm) and B (15–16 mm) beans, making up a large portion of Kenya’s export volume. Slightly smaller than AA but still high quality.
• PB (Peaberry): 15 mesh and above. Peaberries occur when a coffee cherry produces a single rounded bean instead of two flat ones. They make up about 10% of Kenyan lots and are often sorted separately. PB beans can occur in any grade but are graded on their own for quality.
• C Grade: 12–14 mesh. Smaller beans, often lower density. Includes light beans from PB that don’t make higher grades.
• T Grade: 12 mesh and below. These include many defective, broken, or very light beans and are considered low quality.
• TT Grade: Light beans sorted out from AA and AB via air separation. Often lower density or defective despite coming from higher initial grades.
• HE (Hulled Ears): Any beans that don’t fit the other categories due to severe defects or processing issues.

Ungraded and Natural Processed Kenyan Coffees

Not all Kenyan beans go through official grading. Those that don’t are labeled UG (Ungraded), and are divided into:

• UG1: Includes E, AA, AB, and PB grades that somehow missed official grading.
• UG2: Includes C, TT, T, and HE grades — mostly small, defective, or low-density beans.

Beyond washed coffees, Kenya also produces natural (dry-processed) coffees, locally called MBUNI. These beans are sorted by gravity separators and divided into:

• MH (Heavy Mbuni): High-density, yellowish beans free from black or broken beans, insect damage, or stones. These cup with classic natural process flavors and no major defects.
• ML (Light Mbuni): Yellow-green beans that may have slight insect damage or a few black beans, but no foul odors or major taints. Still drinkable, with acceptable cup quality.

What Determines Bean Size and Grade?

Bean size is screened using perforated metal plates — the higher the mesh number, the smaller the holes. Larger beans tend to have developed more evenly during growth, especially at high altitudes (common in Kenya’s 1,200–2,000m coffee zones), and are often denser, which helps with even roasting and better extraction. Peaberries, though not always larger, are sorted by size and evaluated separately due to their unique rounded shape and concentrated flavor potential.

Density and defects also impact grading. Light or chipped beans float away during air separation or fall through lower screens. Heavier, denser beans are considered superior, especially for specialty roasters seeking consistency and cup clarity.

Frequently Asked Questions

What is the highest grade of Kenyan coffee?

The highest commercial grade of Kenyan coffee is AA, which includes beans that are 17–18 mesh in size. These are typically large, dense, and considered top-tier for export. E grade (18 mesh and up) is rarer and also very high quality, often including large peaberries.

What does PB mean in Kenyan coffee?

PB stands for Peaberry, which refers to a coffee bean that forms as a single round bean instead of the usual two flat beans inside a cherry. In Kenya, PB beans are usually sorted separately and make up around 10% of the crop. They are graded on their own and can occur across different size categories.

What is the difference between UG1 and UG2 Kenyan coffee?

UG1 includes higher grades like E, AA, AB, and PB that were not officially graded, while UG2 consists of lower grades such as C, TT, T, and HE — typically smaller, lighter, or defective beans with lower market value.

What are MBUNI coffees in Kenya?

MBUNI refers to Kenyan coffee processed using the natural (dry) method, without washing. These beans are sorted into MH (Heavy Mbuni), which are high-quality yellow beans free of major defects, and ML (Light Mbuni), which may have minor flaws but still cup acceptably.

Why are some Kenyan beans sorted by air?

Air separation is used to remove lighter beans (like TT grade) from heavier ones. Heavier beans generally indicate better density, which correlates with higher cup quality, so this step helps refine the grading process for specialty-grade lots.

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