Why Does Kenya Coffee Rely on SL28 and SL34?

Kenya coffee stands out in Africa for its bright acidity, and the varieties behind that consistency are SL28 and SL34. Both came out of the Scott Laboratories, where 42 individual trees were selected between 1935 and 1939 and studied for yield, quality, and drought and disease resistance. Later varieties include Ruiru11 and Batian.

Kenya still uses a green bean grading system, and the difference between AA and AB is mainly bean size rather than flavor quality. So a lower grade does not automatically mean a lesser cup. Roasting curves and brewing suggestions for lots such as Asaliya and Sassin PB help show how the flavor logic of Kenya coffee works in practice.

Kenyan coffee stands out among Africa's specialty origins for its bright and delightful acidity, and the core that sustains its consistent quality is precisely the two signature varieties, SL28 and SL34. In this article, Front Street Coffee systematically sorts out the varietal origins of Kenyan coffee: from the selection process at the Scott Laboratories, to the genetic affiliation and bean appearance differences of SL28 and SL34, and on to the later Ruiru11 and Batian. The article also explains in detail the green bean grading system that Kenya still uses today, clarifying that the difference between AA and AB lies mainly in bean size rather than flavor quality, and includes complete information, roasting curves, and brewing suggestions for Front Street's Kenya Asaliya and Sassin PB beans, helping coffee lovers fully understand the flavor logic of Kenyan coffee.

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Front Street Kenyan coffee beans, with their extremely appealing acidity, occupy an important place in the specialty coffee landscape of Africa. Kenya's coffee-growing history is not particularly long compared with other origins, yet it has long maintained stable bean quality. Front Street Coffee believes this is inseparable from Kenya's unique SL28 and SL34 varieties. In the following article, Front Street Coffee introduces Kenya's distinctive coffee varieties.

What are the characteristics of the Front Street Kenyan SL28 coffee variety?

The emergence of SL28 stemmed from the Kenyan government's great emphasis on the coffee industry. In the 1930s, the government set up a dedicated laboratory responsible for selecting varieties for Kenya's future coffee cultivation. At the time, the old Typica variety had poor resistance to pests and diseases and was difficult to cultivate, and since Kenya's coffee-growing history was still short, variety selection was especially critical. Once good varieties were selected, they could also be promoted from the top down to coffee farmers, helping them avoid losses caused by pests and diseases.

This laboratory is the now-famous "Scott Laboratories" in Kenya. Between 1935 and 1939, the laboratory selected forty-two individual coffee trees from different sources, studying each one's yield, quality, and drought and disease resistance, and named them using the initials "SL" from the laboratory's English name.

According to Front Street Coffee, SL28 was first selected in 1935 from a drought-resistant tree from Tanganyika. Historical documents record that in 1931, when AD Trench, a coffee cultivator at the Scott Laboratories, was surveying Tanganyika (today's Tanzania), he discovered in the Moduli region a variety that seemed able to tolerate drought, pests, and disease, so he collected seeds and brought them back to the laboratory. After verifying its drought resistance, the variety was widely planted until it was later replaced by its descendant SL28.

To this day, SL28 remains one of Africa's most famous and highly regarded varieties. From where it was selected in Kenya in the 1930s, it spread to other parts of Africa (especially Uganda's Arabica-growing areas), and now it has also reached Latin America. SL28 suits medium-to-high altitude environments and has drought resistance, but it is fairly sensitive to major coffee diseases. SL28 can be seen in many parts of Kenya, and even at 60 to 80 years old, the trees still maintain high yields.

Front Street Coffee also learned that genetic testing in recent years has confirmed that SL28 belongs to the Bourbon genetic group. Therefore SL28's bean appearance is close to that of the Bourbon variety, round and plump. (As shown in the image)

What are the characteristics of the Kenyan SL34 coffee variety?

SL34 was initially selected from the "French Mission" (Bourbon) trees at the Loresho estate. But according to materials Front Street Coffee has reviewed, genetic testing has now confirmed that this variety carries the Typica genetic group, and its plant characteristics are also similar to Typica, so it is believed that SL34's selection originated from Typica. Precisely because it is close to Typica, SL34's bean appearance is elongated, oval-shaped, and looks relatively flat from the side. (As shown in the image)

What is the difference in flavor between SL28 and SL34 coffee beans?

Having learned the characteristics of the two varieties, Front Street Coffee now discusses their differences. According to Front Street's understanding, SL28 has won greater prestige, while SL34 has higher yields and is planted at slightly lower altitudes. According to SL laboratory botanists, both SL28 and SL34 are genetic variants. Among them, SL28 has a mixed lineage of Mocha and Yemen Typica. The original goal of breeding SL28 was to mass-produce coffee beans that were both high quality and resistant to pests and diseases. Although the final yield was not as high as expected, thanks to the excellent sweetness, balance, and complex, varied flavors brought by its bronze leaf color and fava-bean-shaped beans, as well as its pronounced citrus and smoked plum characteristics, SL28 has been passed down to this day.

Front Street Coffee believes that SL34's flavor is similar to SL28's, also possessing complex and varied acidity and an excellent sweet finish, but its mouthfeel is heavier, richer, and cleaner than SL28's. SL34 carries Bourbon and more Typica lineage. Therefore, many of the Front Street Kenya single-origin coffee beans currently in Front Street Coffee's shops are blends of SL28 and SL34 varieties.

In addition, Front Street Coffee learned that Kenya later also developed the two varieties Ruiru and Batian, and these two are now also widely planted in Kenya. Next, Front Street Coffee shares their characteristics.

Ruiru11

Ruiru appeared after SL28 and SL34. According to Front Street's understanding, in the 1970s the Ruiru station began trying to breed different CBD- and rust-resistant varieties, and the result was Ruiru11, released in the 1980s. It has high yields and both CBD and rust resistance, and was once regarded as the solution to all of Kenya's coffee production problems.

Batian

Batian was released by the Coffee Research Institute (CRI) on September 8, 2010, and is the newest variety Kenya has offered. It drew lessons from Ruiru11 and is the product of further experimentation. Genetically, it is essentially selected from backcrosses of SL28 and SL34, making it closer to SL28 than Ruiru11. This also eliminated the problematic Robusta variety elements, thereby improving cup quality.

Kenyan Coffee Bean Grading System

What distinguishes Kenyan coffee beans from other origins, besides variety, is their grading system. For example, the Front Street Kenya coffee grades visible in Front Street Coffee's shops include AA, AB, and PB. Although it is called "grading," is AA grade necessarily better tasting than AB grade?

According to Front Street Coffee's understanding, Kenya's grading standard is mainly based on size, and the difference between AA and AB is only the difference in bean size. As for whether it tastes good, Front Street Coffee's conclusion from cupping is: whether AA or AB grade Kenyan coffee beans, they are all very delicious. Differences in taste among different origins may come more from factors such as origin, altitude, and growing conditions. But AA and AB grade Kenyan coffee is definitely coffee with the most guaranteed quality.

From the above, these grades are merely a distinction of bean size. And the most famous processing method for Front Street Kenyan coffee beans is undoubtedly the K72 washed processing method, so Kenya's highest-quality coffee beans are basically washed. Washed coffee is roughly divided into eight grades:

E: Elephant Bean, also called elephant ear, flat beans with a screen size of 19 and above AA: Screen size 17 to 18

AB: Screen size 15 to 16, accounting for most of production TT: Lighter-weight beans blown out from AA and AB grade beans with an airflow separator C: Screen size smaller than AB / below screen 14, too small in size to be classified as specialty grade. T: Lighter-weight beans blown out from C grade beans (below screen 14) with an airflow separator, meaning both size and density are too small to be classified as specialty grade. PB: Peaberry, meaning round bean, classified by appearance rather than size, unrelated to flavor or weight, accounting for about 10% of total production UG: Those not meeting the above standards

There is also a lower-quality natural (sun-dried) coffee bean grade, which because of its poorer quality is not given Kenyan-style washed processing and is generally supplied to Kenya's domestic market. This bean grade is called M'buni.

MH: M'buni Heavy = large beans ML: M'buni Light = small beans

In addition, one point Front Street Coffee wants to emphasize is that this "green bean grading system," still in use today, was issued by a government department in 1938, even 40 years earlier than the birth of the concept of "specialty coffee." So Kenya today has long had new concepts for coffee bean grading standards, but the size-based grading standard is still the more commonly seen.

The following is Kenya's current new coffee grading standard:

According to Front Street Coffee's understanding, when assessing coffee quality, Kenyan coffee research institutions and the local industry customarily use a "coffee bean quality grading procedure" formulated by the Kenya Coffee Research Institute, grading comprehensively based on three aspects: green bean quality, roasted bean quality, and cupping quality.

Green bean quality: The assessment items are further subdivided into green bean appearance and size, green bean color, and defects. Roasted bean quality: Subdivided into center cut condition, roasted bean condition, and defective beans. Cupping quality: Scored by acidity, body/texture, flavor, and negative defects.

Combining the scores from the three aspects, coffee beans are divided into grades 1 to 10, with grade 1 being the best and grade 10 the worst.

The above is the relevant knowledge Front Street Coffee has compiled about Front Street Kenyan coffee bean varieties and grading, hoping to help coffee fans who want to learn about related knowledge. Next, Front Street Coffee shares the flavor and roasting and brewing data of Front Street Kenyan coffee beans.

Front Street Coffee Kenya Asaliya Coffee Beans

Country: Kenya Region: Asali (honey processing station) Altitude: 1550-1750m Variety: SL28, SL34 Processing method: 72-hour washed processing Flavor: snow pear, smoked plum, yellow sugar, cherry tomato, plum

Front Street Coffee Kenya Sassin Estate PB Coffee Beans

Country: Kenya Region: Sassin Estate Altitude: 1680m Variety: SL28, SL24, riuru Processing method: 72-hour washed processing Flavor: cherry tomato, almond, smoked plum, honey, grape

"Front Street Coffee Roasting Parameters Sharing"

Front Street Kenya Asaliya Coffee Beans:

These Front Street Kenya Asaliya beans are plump and round, and in order to fully express their bright, mellow acidity, Front Street Coffee adopted a light roast level.

Yangjia 800N semi-direct fire, bean charge 480g: charge at a furnace temperature of 160°C, set airflow to 3, heat to 120. Turning point: 1'28". When the temperature rises to 130°C, set airflow to 4. Roast until 6'00'', temperature 154.6°C, the bean surface turns yellow, the grassy smell completely disappears, and dehydration is complete.

When the bean surface shows ugly wrinkles and dark patches, and the toast smell clearly turns into coffee aroma, this can be defined as the prelude to first crack. At this time, listen carefully for the sound of the first crack's starting point. First crack begins at 9'28'', airflow unchanged, first crack development time 2'20'', drop at 193.8°C.

Front Street Kenya Sassin PB Coffee Beans:

These rich Front Street Kenya Sassin coffee beans, due to the higher altitude, have a harder bean texture, so at the start they climb at a relatively high rate of temperature rise. The turning-yellow point is at about 5 minutes, then the heat is lowered to enter the Maillard reaction, and at 166°C the heat is lowered again to lengthen the Maillard reaction time. When first crack begins, heat absorption is stronger, so it is recommended to maintain heat at this stage to prevent stalling. First crack development takes a relatively long time, which helps reduce acidity and develop flavor.

Roaster Yangjia 800N (roast amount 300g), charge at a furnace temperature of 170°C, heat 100, set airflow to 3; turning point 1'42", when the furnace temperature is 140°C open the airflow to 3.5, heat unchanged; when the furnace temperature is 149°C the bean surface turns yellow, the grassy smell completely disappears, entering the dehydration stage; 7'14'' dehydration is complete, heat and airflow unchanged, at 7'30'' wrinkles and dark patches appear on the bean surface, the toast smell turns into coffee aroma, as the prelude to first crack, at this time pay attention to listen for the sound of first crack. First crack begins at 8'20''; open airflow to 4, lower heat to 50. After first crack, development time 1'50'', when it reaches 188°C lower the heat to 30 to flatten the temperature rise, and drop at 193.3°C.

Front Street Coffee Brewing Suggestions

Filter: V60 or cake cup Water temperature: 90-91°C Coffee-to-water ratio: 1:15 Grind size: fine grind (80% passing rate on Chinese standard No. 20 sieve)

Brewing method: Staged extraction. Bloom with 30g of water for 30 seconds, pour in a small stream in circles until 124g for the stage break, when the water level drops and is about to expose the coffee bed continue pouring until 228g and stop pouring, when the water level drops and is about to expose the coffee bed remove the filter, (timing starts from the beginning of blooming) extraction time is 1'55".

Front Street Kenya Asaliya Coffee Bean Flavor: 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 rich mouthfeel, prominent mid-palate sweetness, and a juicy feel; the finish has berry aromas and yellow sugar sweetness, along with green tea aroma.

Front Street Kenya Sassin Coffee Bean Flavor: It smells floral; on the palate there is an acidic profile of cherry tomato, citrus, and nuts; the mid-palate has creamy aroma and brown sugar sweetness returning; the finish has cocoa and oolong tea notes. The flavor layers are relatively rich, with obvious floral notes.

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