How Kenyan coffee beans are graded

Kenya's Strict Green Bean Grading System: Based on "Screen Size"

Unlike many regions that grade by altitude or defect rate, Kenya's official system (Nairobi Coffee Exchange NCE) primarily grades based on the screen size of green coffee beans. While larger beans don't necessarily mean better flavor, they are usually more mature and denser.

AA Grade:

The highest grade for regular export. Screen size 17–18 (diameter approximately 7.2mm or larger). Beans are large and full-bodied, with extremely high density, typically possessing the most intense flavor burst.

AB Grade:

The main grade with the largest output. A blend of Grade A (screen 16) and Grade B (screen 15). Although visually less striking than AA, many high-altitude small-holder AB lots rival AA in cupping flavor and complexity, offering excellent value for money.

PB (Peaberry) Grade:

Peaberry. A natural mutation of coffee beans, where instead of two flat seeds within a single cherry, a single round bean forms (accounting for approximately 5-10% of production). Due to its round shape, it roasts extremely evenly, and the flavor is often very concentrated with intense sweetness.

E (Elephant Bean):

Elephant bean. The largest abnormally sized bean, usually a genetic mutation resulting in a clump of two beans. Extremely rare in production, with a unique profile.

C / TT / T:

Smaller, lighter, or broken commercial/cheap grade beans, less commonly found in the specialty coffee category.

 

Exceptional Lots & Core Varieties: The Legend of Scott Labs

The unique sweet and tart taste of Kenyan coffee is inextricably linked to its coffee varieties:

 SL28 & SL34: The soul varieties of Kenya. Selected by the Scott Agricultural Laboratories in the 20th century. They exhibit excellent drought resistance and display an amazing citrus and blackcurrant acidity in Kenya's volcanic soils.

 K7: Also selected by SL Labs, with better disease resistance and a flavor profile featuring delicate floral and herbaceous notes.

 Ruiru 11 & Batian: Modern disease-resistant varieties bred to combat Coffee Berry Disease (CBD). Previously considered slightly inferior in flavor to the SL series, but with improvements in cultivation and processing techniques, many excellent Batian varieties are now shining in specialty cuppings.

Renowned Micro-regions (Terroir)

Kenya's high-quality coffee is mostly grown in the volcanic ash soils around Mount Kenya, typically at altitudes of 1,500 to 2,100 meters:

 Nyeri: Known for its most intense and bright flavors, characterized by extremely strong citrus and blackcurrant acidity and very high body.

 Kirinyaga: Often possesses extremely high sweetness and complexity, with a beautifully balanced berry and floral profile.

 Kiambu: Close to the capital Nairobi, coffee often exhibits a full chocolate structure and excellent wine-like acidity.

 Embu: Offers a solid mouthfeel with rich tropical fruit, nut, and caramel sweetness.

Most Unique Processing Method: The Signature "72-hour Double Fermentation Washed Method"

Kenya is most renowned for its extremely elaborate washed processing method, which is the core reason for its clean and bright cupping profile:

1. Pulping and Primary Fermentation: After picking extremely ripe red cherries, they are pulped and undergo 12-24 hours of dry fermentation in tanks.

2. Secondary Washing and Re-fermentation: After washing off most of the mucilage, clean circulating water is introduced for a second fermentation.

3. Soaking and Grading: After multiple washes, the coffee beans are soaked in clean water for 12-24 hours (this step is believed to significantly enhance the coffee's bright acidity and cleanliness).

4. African Drying Beds: Finally, they are slowly dried on elevated beds under the sun for 1-2 weeks.

In recent years, Kenya has also started experimenting with small quantities of refined natural processing or experimental anaerobic fermentation, which brings out richer tropical fruit, fermented wine notes, and a fuller body in the beans.

Roasting and Brewing Recommendations

 Roasting: Due to the extremely high density, even moisture content, and hardness of Kenyan beans, they are very resistant to heat. In specialty roasting, there is typically a preference for light to medium-light roasts to fully preserve their prized delicate fruit acidity and floral and fruity aromas. If roasted too dark, the signature blackcurrant acidity can turn into dull smoky or herbaceous notes.

 Brewing: Pour-over or siphon brewing is highly recommended. It is advisable to use a higher water temperature (approximately 91°C–93°C) and a slightly higher coffee-to-water ratio (e.g., 1:15) to fully extract its juicy layers and explosive flavors.