Do Kenyan Coffee Bean Grades Like AA and AB Define Flavor?

Kenyan coffee is often reduced to a cherry tomato note, but that single label does not describe the whole country. The defining trait is a thick, juicy mouthfeel, with acidity and flavor shifting by region. Bean size grades such as AA and AB reflect screen size only and cannot be equated directly with cup quality.

Kenya grows coffee mainly between 1,500 and 2,100 meters with two harvests a year, and the Coffee Board auction prices lots by cupping flavor rather than grade. Varieties SL28 and SL34 plus the K72 coffee bean process, which uses extended washing and soaking, shape the cup. Comparing AB lots from Nyeri Gathaithi and Mugaya shows how altitude pushes flavor in different directions.

Kenya, as a representative producing country of East African specialty coffee, is known for its coffee's full-bodied juiciness and bright acidity. However, many enthusiasts habitually define Kenyan coffee by a cherry tomato flavor, a single standard that Front Street Coffee considers inaccurate. This article systematically outlines Kenya's coffee-producing regions, bean size grading system, auction trading system, the characteristics of the SL28 and SL34 varieties, and the unique K72 washed processing method. At the same time, by comparing the roasting, cupping, and brewing performance of two AB-grade beans, Nyeri Gathaithi and Mugaya, Front Street Coffee demonstrates how altitude differences affect flavor direction, providing coffee enthusiasts with a complete framework for understanding Kenyan coffee.

When many coffee enthusiasts mention Kenyan beans, the first thing that comes to mind is a cherry tomato-like flavor imprint, and some even feel that coffee lacking this tomato note cannot be considered Kenyan coffee. Front Street Coffee holds a different view—a single flavor label should not be used to define all beans from the entire Kenyan producing region. The true regional底色 of Kenyan coffee is actually that thick, full-bodied juicy mouthfeel.

Plant growth cannot be separated from the effects of soil and environment, and coffee trees are no different. Changes in factors such as regional climate and soil conditions cause beans from each harvest season to show differences in flavor. In recent months, Front Street Coffee has cupped many coffees from different regions of Kenya and found that they generally possess a substantial juiciness. Of course, when it comes to specific acidity and flavor details, there are still differences among producing regions.

Kenya is a well-known coffee-producing country in East Africa and also occupies an important position in the global specialty coffee landscape. Kenyan coffee is rich in flavor and highly recognizable, and its trading system is also quite sophisticated. AA or AB grades based on bean size cannot be directly equated with flavor quality. The Coffee Board's auction lots use cupping flavor as the basis for pricing, and the auction prices of specialty Kenyan coffee have remained high. Kenyan coffee is mostly grown at altitudes of 1,500 to 2,100 meters, with two harvest periods each year. To ensure that only ripe cherries are picked, workers must repeatedly inspect the forest, making about 7 rounds back and forth.

Kenya has two coffee sales channels: one is the auction held at the Nairobi Coffee Exchange (the central auction system), through which about 85% of coffee beans are traded; the other is the direct trade model (often called the "second window"), through which only about 15% of beans pass.

The Nairobi Coffee Exchange is the core venue for Kenya's coffee auctions. Auctions are currently held once every two weeks, with bidding fixed on Tuesdays. Twelve days before bidding begins, marketing agents send green bean samples to the NCE for display, giving buyers ample time to select suitable lots for cupping. Each auction usually involves hundreds of beans, sometimes even more than a thousand. The entire process lasts from 9:30 a.m. to around 4 or 5 p.m. without interruption. Inside the venue, dozens of buyers bury themselves in green bean catalogs, bidding while recording the transaction price of each bean.

At present, Kenya's coffee industry chain is roughly as follows: after coffee farmers harvest the cherries, they send them to washing stations, where preliminary density grading is carried out, and then they are handed over to marketing agents. At the washing station stage, beans are graded by screen size into the familiar AA, AB, PB, C, and so on. After that, green bean samples are transferred to the NCE to participate in the auction and provide a catalog. At the auction, buyers bid on green beans that meet their needs, and finally the coffee is exported abroad. It can thus be seen that the NCE is in the middle of the entire industry chain, serving as an auction platform.

Kenyan Coffee Bean Grades

AA Plus (AA+): AA grade with particularly excellent cup quality (flavor, mouthfeel).

AA screen size: 17-18 screen size.

AB screen size: 15-16 screen size, accounting for most of production.

C screen size: smaller than AB.

TT: lighter-weight beans blown out from AA and AB beans by an airflow sorter.

T: lighter-weight beans blown out from C-grade beans by an airflow sorter.

E Elephant Bean: a large mutant bean formed by two beans joined together, also called elephant ear.

PB Peaberry: classified by appearance, unrelated to flavor or weight.

Kenya's coffee-producing areas are mainly six major regions, including: Thika, Kirinyaga, Mt. Kenya West, Nyeri, Kiambu, and Muranga. The harvest periods of the six major regions are from October to December (main crop) and June to August (fly crop). Among them, Nyeri and Kirinyaga are the most famous.

Nyeri is located in the high mountain area near Mount Kenya and is an important producing region for Kenya's specialty-grade coffee, with an average altitude exceeding 1,500 meters. Many high-quality Kenyan coffees come from this area. Nyeri's altitude is high enough, and it is also located east of the Aberdare Mountains and on the ridge between Mount Kenya and the main mountain. The elevated terrain and fertile soil make Nyeri a major center of central Kenya's coffee industry, and related industrial facilities are also quite developed.

The Kirinyaga producing region is located on the slopes of Mount Kenya, at an altitude of 1,300 to 1,900 meters. It is adjacent to the Nyeri producing region and is renowned worldwide for coffee with intense flavor, rich layers, and a solid mouthfeel. Together with Nyeri, it is recognized as one of the two currently finest producing regions in Kenya.

Coffee Bean Varieties

SL28 is a single variety selected in 1935 from a drought-resistant population of Tanganyika origin. SL28 is suitable for cultivation at medium to high altitudes and has drought resistance, but it is relatively susceptible to major coffee diseases. SL28 beans resemble the Bourbon variety, round and plump. In recent years, genetic testing has also confirmed that SL28 belongs to the Bourbon genetic group.

SL34 was first selected in the late 1930s at Kenya's Scott Agricultural Laboratories. SL34 was selected from a tree on Kenya's Kabete Loresho estate, known as the "French Mission." SL34 beans resemble the Typica variety. Front Street Coffee selected beans from Kenyan coffee that resemble Typica, with elongated oval bodies that look relatively flat from the side. In recent years, genetic testing has shown that SL34 is related to the Typica genome.

Coffee Bean Processing Methods

Generally speaking, the washed processing method for coffee beans first removes the skin and pulp of the coffee cherry, leaving only a thin layer of mucilage for washed fermentation for 24 to 48 hours, and finally dries it with machines or sunlight. The Kenyan-style washed processing is different: the entire fermentation process reaches 72 hours.

The Kenyan-style washed processing adopts a repeated cycle of fermentation followed by washing. On the day of harvest, the highest-quality cherries are selected, depulped, and fermented for 24 hours, then washed with clean river water after 24 hours. Next, they are fermented again with clean river water for 24 hours and washed again. This cycle is repeated 3 times, reaching 72 hours, so it is called the Kenyan-style 72-hour fermentation washed processing method, or K72 for short. Front Street Coffee believes that this processing method allows the coffee beans to ferment for a long time at low temperatures, enabling the beans to present a brighter, cleaner, and fuller flavor.

Next, Front Street Coffee compares coffee beans from two producing regions through roasting, cupping, and brewing to see what differences there are in flavor.

Front Street Coffee — Kenya Gathaithi Cooperative AB Coffee Beans

Region: Kenya Nyeri Gathaithi Cooperative

Washing Station: Gathaithi Washing Station

Altitude: 1825m

Variety: SL28&SL34

Processing Method: K72 Washed

Front Street Coffee — Kenya Mugaya AB Coffee Beans

Region: Kenya Mugaya Washing Station

Altitude: 1400m

Variety: SL28&SL34

Processing Method: K72 Washed

Harvest Season: 2020

Front Street Coffee Roasting Record

Gathaithi Coffee Beans

Roasting: The Front Street Coffee roaster used a Yangjia 800N semi-direct fire, with 480g charged. The drum temperature was 165°C when the beans were added, the damper was set to 3, and the heat was 120. Turning point: 1'28''. When the temperature rose to 140°C, the damper was set to 4. Roasted to 6'00'', at 154°C, the bean surface turned yellow, the grassy smell completely disappeared, and dehydration was complete. When ugly wrinkles and dark spots appear on the bean surface, and the toast aroma clearly turns into coffee aroma, it can be defined as the prelude to first crack. At this time, it is necessary to listen carefully for the sound of first crack. First crack began at 9'17'', the damper remained unchanged, the heat was reduced to 90 at 188°C, first crack development time was 2'00'', and the beans were dropped at 193.5°C.

Mugaya Coffee Beans

Roasting: The Front Street Coffee roaster used a Yangjia 800N semi-direct fire, with 480g charged. The drum temperature was 160°C when the beans were added, the damper was set to 3, and the heat was 120. Turning point: 1'28''. When the temperature rose to 130°C, the damper was set to 4. Roasted to 6'00'', at 154.6°C, the bean surface turned yellow, the grassy smell completely disappeared, and dehydration was complete. When ugly wrinkles and dark spots appear on the bean surface, and the toast aroma clearly turns into coffee aroma, it can be defined as the prelude to first crack. At this time, it is necessary to listen carefully for the sound of first crack. First crack began at 9'28'', the damper remained unchanged, first crack development time was 2'20'', and the beans were dropped at 193.8°C.

Front Street Coffee Cupping Report

Front Street Coffee conducts cupping within 8-24 hours after the sample coffee beans are roasted. The cupping bowls generally used by Front Street Coffee baristas are 200ml ceramic bowls. The water temperature used for cupping is 94°C. The grind size is controlled so that the passing rate through a No. 20 standard sieve (0.85 mm) is 70%-75%. The ratio is 11 grams of coffee grounds to 200 milliliters of hot water, that is, 1:18.18, so that the extracted concentration falls exactly within the golden cup range of 1.15%-1.35%, and the steeping time is 4 minutes.

Gathaithi Coffee Beans Dry aroma: citrus; wet aroma: plum; flavor: citrus, plum, berry, honey, grape, tea-like.

Mugaya Coffee Beans Dry aroma: berry; wet aroma: caramel; flavor: smoked plum, plum, grape, caramel, nuts.

From cupping the two beans, it can be noted that the higher-altitude Gathaithi coffee beans have richer acidity. This is because the large temperature difference between day and night at high altitude causes the coffee trees to grow slowly, giving more ample time for coffee flavor formation.

Front Street Coffee Brewing Notes

Dripper: V60 #01

Water Temperature: 90°C

Dose: 15g

Coffee-to-Water Ratio: 1:16

Grind Size: medium-fine grind (77% passing through a No. 20 sieve)

Front Street Brewing Method: First rinse the filter paper and preheat the dripper and coffee pot. Use 30 grams of water for a 30-second bloom, then pour in a small stream in circles until 130 grams for a split pour. When the water level is about to expose the coffee bed, continue pouring until 240 grams and stop pouring. When the water level is about to expose the coffee bed again, remove the dripper. (Start timing from the beginning of the bloom.) The extraction time is 2 minutes.

For more specialty coffee beans, please add the private WeChat of Front Street Coffee, WeChat ID: kaixinguoguo0925

The above content is compiled by CoffeeHunters, a coffee news website.