What defines Kenya coffee grades and the SL28, SL34 varieties?
Kenya coffee is known for bright fruit acidity and rich aroma, produced mainly in East Africa along the equator. The two classic varieties, SL28 and SL34, shape much of that character. Grading by bean size includes AA, AB, and PB, with AA being the largest screen size, though grade does not by itself guarantee cup quality.
The K72 washed processing method gives Kenyan coffee its clean, juicy profile through a long fermentation and soaking step. Seven main producing regions, including Nyeri, Kirinyaga, and Murang'a, each bring slightly different soil and altitude effects. Brewing suggestions usually favor medium roast, a 1:15 ratio, and a pour that highlights the berry and citrus notes.
Kenya, as a major coffee country in East Africa, is renowned worldwide for its bright fruit acidity and rich aroma. This article, from the perspective of Front Street Coffee, systematically sorts out the terroir, historical context, and variety origins of Kenyan coffee, with emphasis on analyzing the background and flavor characteristics of the two classic varieties SL28 and SL34, and breaks down in detail the origins and differences of the grading systems such as AA, AB, and PB. It also introduces the K72 washed processing method and the characteristics of the seven major producing regions, and finally includes Front Street Kenya coffee brewing suggestions and flavor descriptions, providing coffee lovers with a complete knowledge map of Kenyan coffee.
The main cultivation areas of coffee trees are concentrated between the Tropic of Cancer and the Tropic of Capricorn. FrontStreet Coffee here briefly reviews the basic pattern of global coffee distribution with everyone. From an international perspective, coffee mainly comes from three major regions: Africa, Central America, and Asia. Coffee from Asian producing regions often presents herbal and spice-like tones, while coffee from the Americas is known for nuttiness and balance, and African coffee generally has prominent fruity acidity.
The African continent has always been one of the world's finest sources of coffee, famous worldwide for its alluring acidity and aroma, and Kenya is naturally an important member of this group. Kenya is located in East Africa, with the equator passing through it, bordered by the Indian Ocean to the east, Ethiopia to the north, and Tanzania to the south. It is a pivotal coffee-producing country in East Africa and occupies an irreplaceable position in the global coffee landscape. FrontStreet Coffee has always believed that the flavor expression of a coffee bean is inextricably linked to its producing region conditions, cultivation altitude, climate environment, processing method, and variety characteristics. Today, FrontStreet Coffee will explain every aspect of Kenyan coffee for everyone one by one.
Kenyan Coffee Country Introduction
Kenya's official name is the Republic of Kenya. It is located in eastern Africa, with the equator crossing its central part and the East African Rift Valley running through it from north to south. 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. Kenya's terrain is mainly plateaus, with an average altitude of about 1,500 meters. Mount Kirinyaga (also known as Mount Kenya) in the center has an altitude of 5,199 meters, with snow on its summit year-round, and is the second-highest peak in Africa.
In terms of altitude, latitude, and geological conditions, the equator runs through Kenya's territory, placing it exactly within the range of 10 degrees north and south latitude. This is a tropical producing region, with two rainy seasons each year, so coffee can also be harvested twice, with about 60% of production concentrated from October to December and the remaining 40% from June to August. Coffee farms are mainly distributed in the volcanic belt around 1,600 to 2,100 meters above sea level from the capital Nairobi to the Kenyan mountain region. This altitude is very conducive to the formation of coffee bean flavor, because temperatures in the mountains are lower, coffee cherries grow slowly, aromatic substances can fully accumulate, fruit acidity is more prominent, and the beans are also harder. This fertile, crescent-shaped coffee-growing zone is precisely the core producing area of Kenyan specialty coffee beans.
Coffee is Kenya's second-largest agricultural export after tea. Kenyan coffee is mainly Arabica, which is recognized as one of the highest-quality coffee varieties in the world. African coffee-producing regions are generally famous globally for their alluring acidity and aroma, and Kenya is no exception. Kenya is located in East Africa, exactly on the equator, with the Indian Ocean to the east, Ethiopia to the north, and Tanzania to the south. It is a major coffee country in East Africa and one of the extremely important and irreplaceable producing countries.
Kenya is a tropical producing region with two rainy seasons each year, so it can harvest two crops, with 60% concentrated from October to December and the other 40% from June to August. Coffee is mainly grown in the volcanic land around 1,600 to 2,100 meters above sea level from the capital Nairobi to the Kenyan mountain region. This altitude is suitable for the development of coffee bean flavor, because temperatures in the mountains are lower, growth slows down, the aromatic components of the coffee beans can fully develop, the fruity acidity is more obvious, and the texture is also harder. This fertile, crescent-shaped coffee zone is the main producing area of Kenyan specialty beans.
Kenyan Coffee History
In 1878, the British introduced coffee to the African continent and established coffee plantations in Kenya in the 19th century. At that time, Ethiopian coffee beverages were imported to Kenya via South Yemen. However, it was not until the early 20th century that Bourbon coffee trees were introduced to Kenya by the St. Austin Mission. After Kenya gained independence in 1964, the coffee industry continued to develop on the original foundation and has now become a world-renowned high-quality coffee-producing country. Particularly notable is that Kenya established an auction system, successfully avoiding the drawbacks of other coffee-producing countries exploiting small farmers. So-called "fair trade coffee" evolved precisely from this.
Kenyan Coffee Varieties
In Kenya, common coffee varieties include SL28, SL34, French Mission Bourbon, and Ruiru 11.
The Origin of the SL28 Variety
According to documented records, in 1931 an official from the Scott Laboratories went to Tanganyika (present-day Tanzania) to conduct field research. He noticed that a coffee tree grown in the Moduli area seemed tolerant to drought, disease, and pests, so he collected the seeds and brought them back to the Scott Laboratories. In 1935, the laboratory selected a single tree type from the Tanganyika drought-resistant population, and after repeated breeding and improvement, finally released SL28, a descendant of the Moduli area. In recent years, genetic research has confirmed that SL28 belongs to the Bourbon genetic group.
Characteristics of the SL28 Variety
The SL28 variety is easy to cultivate and requires no special care. Its beans are relatively large and its yield is high, and its flavor quality is quite outstanding. Since its release by the Kenyan authorities in the 1930s, it was first planted in Kenya and then spread to Uganda. It is currently also widely noticed in Central America. This variety is suitable for medium to high altitudes and has drought resistance, but it is still susceptible to major coffee diseases.
Coffee Flavor of the SL28 Variety
The flavor of the SL28 variety indeed carries the bright tone of original Bourbon, and even has the rich acidity of original Mocha varieties, while also possessing complex flavor and a dense mouthfeel. Although SL28's yield later fell short of expectations, its copper-colored leaves and broad-bean-shaped beans have excellent sweetness, balance, and complex, changeable flavor, as well as prominent citrus and smoked plum characteristics. Its strong fruit acidity, rich mouthfeel, and beautiful balance are impressive. What is most special is that only when planted in Kenya can SL28 display such a distinct tone; SL28 planted in other countries can only present a similar flavor.
FrontStreet Coffee: Kenya Asali Coffee
Producing Region: Thika, Kenya
Processing Station: Asali Honey Processing Station
Altitude: 1,550–1,750 meters
Grade: AA TOP
Varieties: SL28, SL34
Processing Method: Kenyan 72-hour washed
Roasting Suggestions
This bean is full and round. In order to fully express its bright, mellow acidity, a light roast is used.
Machine: Yangjia 800N, 550g green beans charged
Charge Temperature: 200°C
First Crack: 5'30", 154.3°C
Developed for 2'10'' after first crack, discharged at 191.6°C
Brewing Suggestions
Dripper: Hario V60
Water Temperature: 90°C
Dose: 15 grams
Coffee-to-Water Ratio: 1:15
Grind Size: Medium-fine grind (EK43s setting 10)
Brewing Method
Pulse Pouring Extraction
Use 30 grams of water for blooming for 30 seconds, then pour in a slow circular stream to 125 grams for the first pulse. When the water level is about to expose the coffee bed, continue pouring to 225 grams and stop. When the water level is about to expose the coffee bed again, remove the dripper. (Timing starts at the beginning of blooming.) The extraction time is 2 minutes.
Front Street Kenya Coffee Flavor Description
The wet aroma has ripe tomato and floral notes. On the palate, there are flavors of cherry tomato and smoked plum, with bright acidity, a clean and at the same time the most solid and rich mouthfeel, like the weight of an African elephant! The mid-palate has outstanding sweetness and a juicy feel, and the finish has berry aroma, brown sugar sweetness, and green tea aroma.
SL34 Variety
According to materials reviewed by Front Street, SL34 was a variety initially selected at the Scott Agricultural Laboratories in Kenya in the 1930s. Kenya's Scott Laboratories selected from individual coffee trees between 1935 and 1939 and named them "SL" varieties. SL34 was selected from a single coffee tree at the Loresho Estate in the Kabete area of Kenya. That coffee tree was labeled "French Mission."
French missionaries such as the Spiritans established a mission in Bura in the Taita Hills of Kenya, and introduced Bourbon coffee seeds from La Réunion island for planting. In 1899, coffee seedlings were then brought from the Bura village to other French mission stations at Saint Austin for planting. These coffee seeds were spread throughout the region for coffee bean production. This is the origin of the so-called "French Mission coffee."
Historically, coffee seeds from Réunion were spread by French missionaries, and French Mission is considered another name for Bourbon coffee. However, modern genetic testing has confirmed that SL-34 has the genetic group of Typica. It turns out that the legend that SL-34 was selected from the French Mission coffee group is very likely incorrect. SL34 is a mutation between Typica and Bourbon, and its difference from SL-28 lies in its bronze-colored young leaves, indicating that this variety is closer to Typica. SL34 has strong resistance to heavy rain at high altitudes and very high cup quality, with citrus acidity and a thick mouthfeel.
FrontStreet Coffee: Kenya Sasini Estate Washed AA
Origin: Kiambu producing region
Estate: Sasini Estate
Altitude: 1,650 meters
Grade: AA
Varieties: SL28, SL34
Processing Method: Washed
Roasting Curve
FrontStreet Coffee Barista Brewing Suggestions
Dripper: Hario V60
Water Temperature: 90°C
Dose: 15 grams
Coffee-to-Water Ratio: 1:15
Grind Size: Medium-fine grind (EK43s setting 10)
Brewing Method Sharing — Pulse Pouring Extraction
Use 30 grams of water for blooming for 30 seconds, then pour in a slow circular stream to 125 grams for the first pulse. When the water level is about to expose the coffee bed, continue pouring to 225 grams and stop. When the water level is about to expose the coffee bed again, remove the dripper. (Timing starts at the beginning of blooming.) The extraction time is 2 minutes.
Front Street Kenya Coffee Pour-Over Flavor Description
Obvious smoked plum, cherry tomato, and honey notes, with a slight nuttiness when cooled, a juice-like mouthfeel, and bright acidity.
Ruiru 11
In 1985, there was a global outbreak of coffee leaf rust. Against this background, Kenya developed a hybrid variety that emphasized yield over quality, but its flavor quality was far inferior to the previous SL28 and SL34, and it did not develop in the specialty coffee world. However, many coffee suppliers, even those importing famous coffees, mix this hybrid bean into blends to reduce costs.
Kenyan Coffee Grading
Kenyan coffee beans began using a strict grading system in the 1930s, mainly based on the size, shape, and hardness of the coffee beans. From high to low, they are divided into AA or AA+, AB, PB, C, E, TT, and T. This can be used as a basis for selection, and coffee flavor is also used as a reference. At present, the grades commonly seen in the mass market are AA, AB, and PB.
E (Elephant Bean): Here "E" stands for "Elephant," but it is not the elephant bean variety in coffee varieties. It is a bean formed by abnormal development in which two seeds intertwine with each other and form what appears to be "one bean." It is considered a defect. Generally speaking, there are two seeds in one fruit, pressed face to face, so one side is flat, and these are called flat beans, female beans, or double beans. E refers to two seeds that during the growth process fuse and stick together, becoming an extra-large bean. Grade E has a screen size of about 18 mesh (one mesh is 1/64 inch) or above, and the quantity is scarce.
AA: This grade is about 17–18 mesh (about 6.7–7.1 mm) in size. It is the Kenyan coffee grade most people have heard of, and in specialty coffee this grade is usually called AA TOP. It is also a bean that many coffee shops promote. However, AA does not necessarily mean it is the best; this is only about bean size and cannot be confused with flavor.
AB: Most coffee beans fall into this grade. It is called AB mainly because the screen aperture for A is 6.80 mm and for B is 6.20 mm, and these two sizes of coffee beans (Grade A and Grade B) are mixed together for sale, so it is called AB. The size is about 15–16 mesh (about 6.0–6.4 mm).
C: The bean size is roughly between 14–15 mesh (about 5.6–6.0 mm), slightly smaller than Grade B.
PB: In English it is called Peaberry. In Taiwan it is often called small round bean, and it can also be called male bean or single bean. Compared with ordinary flat beans, this is also quite rare, accounting for about 10% of all coffee beans. It is mainly because only one seed develops fully inside the fruit, resulting in a small, round bean. Some people especially like the flavor of PB, so PB is sorted out and sold separately.
TT: This type of coffee bean is the light bean screened out from AA and AB beans by an airflow separator. It is usually light in weight and does not meet hardness standards, and also contains broken and defective beans.
T: Lighter-weight beans screened from Grade C beans, mixed with damaged beans and even fragments of broken beans.
MH/ML: This type of coffee bean is not exported. It usually consists of overripe coffee beans that have fallen to the ground, with poor quality. It accounts for about 7% of all coffee beans and is only supplied to Kenya's domestic market.
Kenyan Coffee Grading — Where Do AA TOP and AB TOP Come From?
In fact, in addition to the official version of Kenyan coffee grading, Kenyan exporters or traders have also created special grades (unofficial) for AA and AB. Common ones include: AA TOP, AA+, AA++, AB+, AB TOP, and AA FAQ, among other Kenyan coffee grades.
FAQ is the abbreviation of Fair Average Quality in English, meaning average fair quality, and is the basic version of the AA grade. But categories such as AA TOP, AB TOP, and AA+ actually have no specific standard. It does not mean that two "+" signs necessarily make it taste better or have better flavor. Why?
The main reason is that this is not a unified standard. Every green bean trader or different person may produce different results. It is possible that one company's AA+ is comparable in flavor to another company's AA++. So everything ultimately comes back to cupping during your own roasting. That is the most practical!
Kenyan Processing Methods
Just as honey processing is to Costa Rica and wet-hulling is to Indonesia, when mentioning Kenyan coffee, how can we not mention the K72 processing method?
Kenyan-style 72-hour Fermentation Washed Processing Method
Originating in Kenya, it adopts a repeated cycle processing method of fermentation followed by washing. After harvest, processing is done on the same day, selecting the highest-quality cherries for pulping and fermentation. The fermentation time is 24 hours, and after 24 hours they are washed with clean river water. Then they are fermented again with clean river water for 24 hours and washed again. After repeating this cycle three times, it reaches 72 hours, so it is called the Kenyan-style 72-hour fermentation washed processing method, or K72 for short.
First Washing and Fermentation
After the coffee cherries are harvested, they first undergo water flotation density sorting. The principle is to use differences in the density and mass of the coffee fruit itself for screening; coffee beans with high density (heavy mass) sink in water, while coffee beans with low density float. Fully ripe, high-quality coffee cherries have high density, and these are selected for further processing.
After selecting high-quality, sufficiently ripe fruit, the skin is removed and the beans are soaked in water for washing, allowing the mucilage attached to the outer layer of the green beans to undergo fermentation. Pectin has natural sugars and alcohols, which play a crucial role in the development of coffee sweetness, acidity, and overall flavor. The fermentation time lasts as long as 24 hours. After fermentation, 80–90% of the pectin can be removed, leaving only the flavor inside the coffee beans.
Second Washing and Fermentation
Next comes the second washing and fermentation procedure. After the coffee beans from the previous stage are cleaned, they are soaked in water again for 24–48 hours. This process increases proteins and amino acids, and the acidity of the coffee beans thereby develops complex and delicate layers of mouthfeel. Finally, all remaining pectin is removed, and the coffee beans are moved to raised drying beds for sun drying.
The fermentation time lasts as long as 24 hours. After fermentation, 80–90% of the pectin can be removed, leaving only the flavor inside the coffee beans.
Finally, all remaining pectin is removed, and the coffee beans are moved to raised drying beds for sun drying. The drying time depends on weather conditions and generally takes about 5–10 days to complete.
How Many Coffee Producing Regions Are There in Kenya?
The Kenyan coffee producing regions are most famous for seven major regions: Thika, Kirinyaga, Mt. Kenya West, Nyeri, Kiambu, Ruiri, and Muranga. Among them, the foothills of Mt. Kenya and Aberdare are the main producing areas.
The flavor of each producing region in Kenya is very different. Kenya is divided into 47 counties nationwide. The coffee characteristics of different counties are distinct. Kenyan coffee trees are mostly planted at 1,400–2,000 meters above sea level and are harvested twice a year. The growing regions include Ruiri, Thika, Kirinyaga, Mt. Kenya West, Nyeri, Kiambu, and Muranga. The foothills of Mt. Kenya and Aberdare are the main areas. For example, through cupping, Front Street found that coffee from the Embu producing region has a balanced mouthfeel, as well as citrus fruit, chocolate, apple, and acidity; while coffee from the Nyeri producing region mostly features white grape, juicy feel, grapefruit, and cherry tomato flavors, full of fruitiness and sweet like caramel.
Main Kenyan Coffee Producing Regions:
NYERI
NYERI: Located in central Kenya, Nyeri is where the extinct volcano Mount Kenya is situated. The red soil of this region nurtures Kenya's best coffee. Agriculture is extremely important here; coffee is one of the most important crops. Cooperative societies composed of smallholders are more common than large estates. This region has two harvests, but coffee from the main season is usually of higher quality. This producing region is known for thick acidity like blackberry as well as floral and fruity aromas.
Altitude: 1,200–2,300 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Ruiru 11, Batian.
MURANG'A
MURANG'A: This region under Central Province has about 100,000 coffee farmers. This producing region is not far from Nairobi and was one of the places first chosen by missionaries to settle because the Portuguese prohibited them from living in the coastal area. This is another producing region that benefits from volcanic soil, with more smallholder coffee farmers than estates. It has relatively bright acidity.
Altitude: 1,350–1,950 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Ruiru 11, Batian
EMBU
EMBU: This region near Mount Kenya gets its name from Embu town. About 70% of the local population is engaged in small-scale farming, and the most popular cash crops in the area are tea and coffee. Almost all coffee comes from smallholders, and this region's production is relatively small. The acidity is not as strong as Nyeri, but fortunately the flavor is balanced enough.
MERU
MERU: Most coffee in this region is grown by smallholders on the foothills of Mount Kenya and the Nyambene Hills. The name refers to the magnetic field area and the Meru people living there. In the 1930s, they were the first Kenyans to begin producing coffee. This was because of the Devonshire White Paper signed in 1923, which guaranteed the importance of the rights of African people in Kenya.
Altitude: 1,300–1,950 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Ruiru 11, Batian, K7
KIAMBU
KIAMBU: This producing region in central Kenya has the highest-altitude coffee-growing areas in the region, and Thika also belongs to this producing region. However, some coffee trees at high altitudes suffer from dieback and then stop growing. This producing region is named after the town of Nakuru. Coffee here is grown both on estates and by smallholders, but production is relatively small. This producing region is a traditional tea-growing area, and the coffee beans have vanilla and floral aromas.
Altitude: 1,850–2,200 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Ruiru 11, Batian
KISII
KISII: This region is located in southwestern Kenya, not far from Lake Victoria. It is a relatively small producing region, and most coffee beans come from cooperative societies composed of small producers.
Altitude: 1,450–1,800 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Blue Mountain, K7
TRANS-NZOIA, KEIYO & MARAKWET
TRANS-NZOIA, KEIYO & MARAKWET: This small producing region in western Kenya has begun to develop in recent years. Mount Elgon provides a certain altitude, and most coffee comes from estates. Coffee planting is usually intended to diversify farms that previously had only cornfields or dairy.
Altitude: 1,500–1,900 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: Ruiru 11, Batian, SL-28, SL-34.
KIRINYAGA
The producing region is located on the slopes of Mount Kenya, adjacent to Nyeri, and is famous worldwide for coffee with strong flavor, rich layers, and a solid mouthfeel. Together with Nyeri, it is recognized as one of the two best producing regions in Kenya today. Most producers in this region are small coffee farmers who join cooperatives, and the cooperatives play an integrating role, providing washing stations, while coffee farmers send coffee cherries to the cooperatives' processing stations for green bean processing. Originally this referred to Mount Kenya itself, but when the British colonized, they found the name hard to remember, so they changed the mountain's name to Mt Kenya and no longer called it Kirinyaga. It comes from the Kikuyu people and means "white mountains," and is considered the place where the gods reside. The Kikuyu are the largest ethnic group in Kenya, accounting for one-fifth of the total population.
Altitude: 1,300–1,900 meters
Harvest Period: October–December (main season), June–August (secondary season)
Varieties: SL-28, SL-34, Ruiru 11, Batian.
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The above content is compiled by CoffeeHunters, a coffee news website.
