How does the Kenyan coffee grading system set AA and AB apart?

Kenya AA and AB are grades for Kenyan green coffee beans, not varieties or brands. AA marks the largest bean size class, while AB combines A and B sizes. The labels reflect bean size standards and cup quality differences, which is why the two grades can differ in price even when they come from the same region.

The article sorts out Kenya's seven main producing regions, the SL28 and SL34 varieties, and the 72-hour washed coffee bean process known as K72. It also covers PB grade, plus roasting curves, cupping reports and brewing parameters for AA TOP from the Asali processing factory in Thika.

Kenyan coffee is famous for its rich berry notes and solid mouthfeel, but when faced with grading labels like AA and AB, many people are not clear about what they actually represent. From Front Street's perspective, this article systematically sorts out Kenya's seven major producing regions, the origins and flavor differences of the main varieties SL28 and SL34, analyzes the uniqueness of Kenya's 72-hour washed processing method (K72), and explains in detail the bean size standards and cup quality differences of grades such as AA, AB, and PB. It also includes Front Street's roasting curve, cupping report, and brewing parameters for AA TOP from the Asali processing factory in the Thika region, helping coffee lovers fully understand the complete logic of Kenyan coffee from origin to cup.

When mentioning coffee-producing countries in Africa, most people think of either Ethiopia or Kenya. The former's coffee is known for its bright and clean acidity, while the latter conquers the palate with its full-bodied berry texture. The richness reminiscent of tomato juice and the acidity of smoked plum have both become signature memories of Kenyan coffee. Many friends ask Front Street's baristas the same question: what exactly does Kenya AA mean?

In fact, AA is a set of grading standards for Kenyan green coffee beans. Next, Front Street will guide everyone through a complete understanding of this East African coffee powerhouse, from producing regions, variety characteristics, roasting approaches, and cupping performance to brewing methods.

Overview of Kenyan Coffee Producing Regions

Kenya is located in eastern Africa, with the equator passing through the middle of the country and the East African Rift Valley running from north to south across the entire territory. It borders Somalia to the east, Tanzania to the south, Uganda to the west, Ethiopia and Sudan to the north, and faces the Indian Ocean to the southeast. The country's terrain is mainly plateau, with an average altitude of about 1,500 meters. In the center, the towering Kirinyaga Peak (namely Mount Kenya) rises 5,199 meters above sea level, with snow on its summit year-round, second in height in Africa only to Mount Kilimanjaro.

Kenya has seven most renowned coffee-producing regions: Thika, Kirinyaga, Mt. Kenya West, Nyeri, Kiambu, Ruiru, and Muranga. Among them, the foothills of Mount Kenya and the Aberdare Range are the core cultivation areas. For specialty coffee, the beans produced in the four regions of Thika, Nyeri, Kirinyaga, and Muranga are the most outstanding.

Nyeri Producing Region: Located in central Kenya, it is home to the extinct volcano Mount Kenya. The red soil here nourishes Kenya's highest-quality coffee. Agriculture holds an extremely important position locally, and coffee is its main cash crop. The region is dominated by cooperatives formed by smallholder farmers, while large estates are rare. The altitude range is 1,200 to 2,300 meters. The main harvest season is from October to December, and the secondary harvest season is from June to August.

Muranga Producing Region: Under Central Province, with about 100,000 coffee growers in the area. This inland producing region was one of the first places where missionaries chose to settle, because the Portuguese had once forbidden them from living in coastal areas. Muranga also benefits from volcanic soil, and the number of smallholder farmers clearly exceeds that of estates. The altitude is 1,350 to 1,950 meters. The main harvest season is October to December, and the secondary harvest season is June to August.

Kirinyaga Producing Region: Located on the slopes of Mount Kenya and adjacent to the Nyeri producing region, it is renowned worldwide for coffee with intense flavor, rich layers, and a full body, and together with Nyeri it is currently one of Kenya's two top producing regions. Most producers in this region are small coffee farmers who join cooperatives, and the cooperatives uniformly provide wet mills. Farmers send the harvested coffee cherries to the processing factories for processing.

"Kirinyaga" was originally the name of Mount Kenya. British colonists found the word difficult to remember, so they changed the mountain's name to "Mt Kenya" and stopped using "Kirinyaga." Mount Kenya is Africa's second-highest peak. Although located in the tropics, its summit is covered with snow year-round, and the original meaning of Kirinyaga is precisely "white summit." Mount Kenya is not only a UNESCO protected area; wildlife also gathers to feed on the surrounding foothills and grasslands, making it a favorite attraction for tourists. The word "Kirinyaga" comes from the Kikuyu people and means "white mountains," regarded as the place where the god resides. The Kikuyu are Kenya's largest ethnic group, accounting for one-fifth of the total population. The altitude is 1,300 to 1,900 meters. The main harvest season is October to December, and the secondary harvest season is June to August.

Thika Producing Region: Located in the town around Kenya's capital, Nairobi. A large number of coffee fields are distributed around Nairobi. Thika itself is an industrial town, but it is surrounded by farmland and waterfalls. There are about 2,000 coffee farmers in the Thika area. The history of coffee cultivation there can be traced back to the late nineteenth century, when coffee tree species were introduced from the northern neighboring country Ethiopia. After local variety improvement, currently common varieties include Bourbon, Kents (SL34, SL28), Typica, and Riuri 11. At present, about ninety percent of the planted varieties are SL34 and SL28. The new variety Batian, released in 2007, has not yet been widely promoted. The flavor characteristics of the Thika producing region are bright fruit acidity, a thick berry juice sensation, and honey-like sweetness. The altitude is 1,550 to 1,750 meters.

Kenyan Coffee Varieties

SL28 Variety

SL28 is one of Africa's most famous and highly regarded coffee varieties. Since being selected in Kenya in the 1930s, it has spread to other parts of Africa (especially Uganda's arabica-growing areas), and today it has also spread to Latin America. SL28 is suitable for cultivation at medium to high altitudes and has drought resistance, but it is relatively susceptible to major coffee diseases. SL28 can be seen in many parts of Kenya, and even at 60 to 80 years of age, the trees still remain highly productive.

SL28 is a single variety selected in 1935 from a drought-resistant population in Tanganyika. In 1931, a senior coffee officer from the Scott Laboratories (A.D. Trench) led visitors to Tanganyika (present-day Tanzania). According to historical records, he noticed that a variety growing in the Modì area seemed tolerant to drought, disease, and insect pests. Seeds were collected and brought back to the Scott Laboratories, and their drought resistance was subsequently verified.

SL34 Variety

SL34 was first selected in the late 1930s at Kenya's Scott Agricultural Laboratories. It came from a tree at Kenya's Kabete Loresho estate, and this tree was called the "French Missionary." In 1893, French missionaries established a mission in Taita Hills, Kenya, and planted Bourbon coffee seeds brought from Réunion Island. In 1899, coffee seedlings from Taita were sent to another French mission at St. Austin (near Nairobi), and seeds were distributed from there to settlers willing to grow coffee. This is the origin of "French Missionary" coffee. Because French missionaries historically shipped seeds directly from Réunion Island, the outside world generally understood "French Missionary" as Bourbon variety. However, recent genetic testing shows that SL34 is related to the Typica genome, so the claim that SL34 originated from French Missionary has also sparked different disputes.

After cupping the coffee beans of the two varieties separately, Front Street believes that SL28 and SL34 have similar flavors, both presenting complex and changeable berry-like acidity and a caramel-sweet finish. Compared with SL28, SL34 has a heavier body, and its acidity leans more toward dark berries such as blackberry. The overall sweetness and acidity are balanced, with a caramel aftertaste. SL28, on the other hand, tends more toward blueberry-like acidity after the temperature drops, with acidity rising slightly and sweetness also higher, consistent with Bourbon's characteristic high sweetness.

Kenyan Coffee Bean Processing Method — Kenya 72-Hour Wash

Kenya adopts a repeated cycling processing method of fermentation followed by washing: post-processing is carried out on the day of harvest, selecting the highest-quality coffee cherries, depulping and fermenting them. The first fermentation lasts 24 hours, after which they are washed with clean river water. Then they are fermented again with clean river water for 24 hours and washed again. This cycle is repeated three times, totaling 72 hours, hence the name Kenyan-style 72-hour fermentation washed processing method, abbreviated as [K72]. Front Street believes that this processing method allows the coffee beans to undergo long fermentation at low temperatures and finally complete the entire process after drying and dehydration, giving the beans a brighter, cleaner, and fuller flavor.

Kenyan Coffee Bean Grading

AA Plus (AA+): AA grade with particularly excellent cup quality (flavor, mouthfeel). AA: Screen Size 17-18. AB: Screen Size 15-16, accounting for most of production. C: Screen Size smaller than AB. TT: Lighter beans blown out from AA and AB grade beans using an airflow sorter. T: Lighter beans blown out from C grade beans using an airflow sorter. E Elephant Bean: Large mutant bean formed by two beans joined together, also called elephant ear. PB Peaberry: Classified by shape, unrelated to flavor and weight.

Producing Region: Thika, Kenya

Processing Factory: Asali Honey Processing Factory Altitude: 1,550-1,750 meters Grade: AA TOP Variety: SL28, SL34 Processing Method: Kenya 72-hour wash

Front Street Roasting Suggestions

Preheat the roaster to 200°C and charge the beans, set the damper to 3, turn on the flame after 30 seconds, adjust the heat to 160, keep the damper unchanged, the turning point is 1 minute 34 seconds, maintain the heat, turn yellow at 5 minutes 30 seconds, the grassy smell disappears, entering the dehydration stage, lower the heat to 130, reduce the heat to enter the Maillard reaction, and when it reaches 178°C lower the heat again to prolong the Maillard reaction time, and open the damper to 3.5.

At 7 minutes 45 seconds dehydration is complete, lower the heat to 80. At 8 minutes 30 seconds wrinkles and dark streaks appear on the bean surface, the toast aroma turns into coffee aroma. This is the prelude to first crack, and at this point pay attention to listening for the sound of first crack. At 8 minutes 52 seconds first crack begins, open the damper fully to 5, lower the heat to 50, and reduce the degree of caramelization. When first crack begins, heat absorption is relatively strong, so it is recommended to maintain heat at this stage to prevent stalling. First crack development takes more time, which helps reduce acidity and develop flavor. Post-first-crack development time is 2 minutes 10 seconds, and drop the beans at 191.6°C.

Front Street Cupping Report

The wet aroma has ripe tomato and floral notes. On the palate it presents cherry tomato and smoked plum flavors, with bright acidity, a clean mouthfeel, medium body, prominent mid-palate sweetness, and a juicy sensation. The finish is berry aroma and yellow sugar sweetness, accompanied by green tea fragrance.

Front Street Brewing Suggestions

FrontStreet Coffee, considering that this bean uses a medium-light roast profile, will choose a higher water temperature and a faster-flow dripper. The main purpose is to extract its bright acidity with high temperature, but it does not want high temperature to cause over-extraction, so it chose the faster-flow V60 dripper.

Coffee-to-water ratio: 1:15, 15 grams coffee: 225 milliliters water

Water temperature: 90°C~91°C Grind size: fine granulated sugar (78% passing through a No. 20 standard sieve)

For the first pour, add 30 grams of water for a 30-second bloom, then pour 95 grams (the digital scale shows about 125 grams), finishing the pour in about 1 minute. When the water level drops to two-thirds of the coffee bed, pour the remaining 100 grams (the digital scale shows about 225 grams), finishing the pour in about 1 minute 40 seconds. Dripping is completed at 2 minutes 00 seconds. Remove the dripper and finish extraction.

Brewed flavor: On the palate there are smoked plum and cherry tomato flavors. In terms of mouthfeel, the acidity is intense and full, with prominent mid-palate sweetness and a juicy sensation. The finish has berry aroma and yellow sugar sweetness, along with green tea fragrance.

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