Why are Kenya SL28 and SL34 varieties so valued?

Kenya coffee stands out in Africa's specialty regions for bright, pleasant acidity, and the steady quality behind it comes largely from two local varieties: SL28 and SL34. Both were selected by the Scott Laboratories, which from 1935 to 1939 evaluated forty-two single trees for yield, quality, drought resistance and disease resistance, naming them with the lab's initials.

Kenya's growing history is short by regional standards, so top-down variety selection mattered. SL28 was first selected in 1935 from a drought-resistant tree of Tanganyika origin. Later varieties such as Ruiru11 and Batian followed. Kenya also grades green beans, and understanding that system helps buyers judge lots beyond the variety name alone.

Kenyan coffee stands out among Africa's specialty regions with its bright and pleasant acidity, and the core that sustains its stable quality is precisely the two local varieties, SL28 and SL34. In this article, Front Street Coffee will systematically sort out the origins, botanical characteristics, and flavor differences of these two varieties, while also introducing later-developed varieties such as Ruiru11 and Batian, as well as the ins and outs of Kenya's green bean grading system. In the latter part of the article, we will also share the roasting parameters and brewing suggestions for Front Street Kenya Small Tomato and Sachini PB, for coffee enthusiasts to reference and practice.

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Front Street Kenya coffee beans occupy an important position in Africa's specialty coffee landscape with their pleasant acidity, though Kenya's coffee-growing history is not particularly long compared to other regions, it has nevertheless maintained stable bean quality over the long term. Front Street Coffee believes this is inseparable from Kenya's unique two major varieties, SL28 and SL34. Below, Front Street Coffee will introduce Kenya's unique coffee varieties.

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

The birth of SL28 is directly related to the Kenyan government's emphasis on the coffee industry. In the 1930s, the Kenyan government established a dedicated laboratory responsible for selecting varieties for future coffee cultivation. At the time, the ancient Typica variety had weak resistance to pests and diseases and was difficult to manage, while Kenya's coffee-growing history was short, making variety selection particularly critical. Once good varieties were selected, they could be promoted top-down to coffee farmers nationwide, helping them avoid pest risks.

This laboratory is precisely the now-famous Kenyan "Scott Laboratories." Between 1935 and 1939, the laboratory selected forty-two coffee single trees from various sources, conducting research on yield, quality, drought resistance, and disease resistance, and naming them with the first letters "SL" from the laboratory's English name.

According to Front Street Coffee's understanding, SL28 was first selected in 1935 from a single tree among drought-resistant trees originating from Tanganyika. Historical records show that in 1931, when AD Trench, a breeder at Scott Laboratories, traveled to Tanganyika (present-day Tanzania) for investigation, he discovered a variety in the Moduli area suspected of being resistant to drought and pests, so he collected seeds and brought them back to the laboratory. After drought resistance was verified, this variety was widely planted until it was replaced by its descendant SL28.

To this day, SL28 remains one of the most famous and highly regarded varieties in Africa. From its original selection in Kenya in the 1930s, it gradually spread to other parts of Africa (especially Uganda's Arabica-growing areas), and now has spread to Latin America. SL28 is suited to medium-to-high altitude environments, has drought resistance, but is relatively sensitive 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 produce considerably.

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

What are the characteristics of the Kenya SL34 coffee variety?

SL34 was initially selected from the "French Mission" (Bourbon) on the Loresho estate. However, after consulting materials, Front Street Coffee learned that this variety has been confirmed by genetic testing to carry the Typica genetic group, and its plant performance characteristics are also similar to Typica, so it is believed that SL34's selection source is Typica. Precisely because it is close to Typica, SL34's bean appearance is slender and oval, appearing somewhat flat from the side. (As shown in the picture)

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

Having understood the characteristics of the two varieties, Front Street Coffee will now talk about their differences. According to Front Street's understanding, SL28 has won higher prestige, while SL34 has higher yield and is grown at slightly lower altitudes. According to botanists at SL Laboratories, both SL28 and SL34 are genetic variants. Among them, SL28 has a mixed lineage of Mocha and Yemen Typica. The goal of breeding SL28 back then was to mass-produce coffee beans with both high quality and pest and disease resistance. Although the final yield did not meet expectations, thanks to its bronze leaf color and fava-bean-shaped seeds that bring excellent sweetness, balance, and complex and varied flavors, plus its prominent citrus and smoked plum characteristics, SL28 has been passed down to this day.

Front Street Coffee believes that SL34's flavor direction is similar to SL28, also possessing complex and varied acidity and an excellent sweet finish, but with a heavier, more intense body than SL28, and also cleaner. SL34 carries Bourbon as well as more Typica lineage. Therefore, many of the Front Street Kenya single-origin coffee beans currently in Front Street Coffee's store are blends of SL28 and SL34.

In addition, according to Front Street Coffee's understanding, Kenya later also developed two varieties, Ruiru and Batian, which are currently also widely planted in Kenya. Next, Front Street Coffee will share the characteristics of these two coffee beans.

Ruiru11

Ruiru appeared after SL28 and SL34. According to Front Street's understanding, in the 1970s, the Ruiru station began attempting to breed different CBD and rust-resistant varieties, and the result was Ruiru11, released in the 1980s. It has high yield and combines CBD and rust resistance, and was once regarded as a solution to various problems in Kenyan coffee production.

Batian

Batian was released by the Coffee Research Institute (CRI) on September 8, 2010, and is Kenya's newest variety to date. It learned lessons from Ruiru11 and conducted further experiments. From a genetic perspective, Batian was essentially selected from backcrosses of SL28 and SL34, being closer to SL28 than Ruiru11, thereby eliminating problematic Robusta variety elements and improving cup quality.

Kenya Coffee Bean Grading System

Kenyan coffee beans differ from other regions not only in varieties but also in their grading system. For example, the common Front Street Kenya coffee grades in Front Street Coffee's store 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 lies only in bean size. As for whether it tastes good, Front Street Coffee's conclusion through cupping is: whether AA or AB grade Kenyan coffee beans, they are all very delicious coffees. Differences in taste between different regions may stem more from factors such as region, altitude, and growing conditions. But AA and AB grade Kenyan coffee is definitely coffee with the most guaranteed quality.

As mentioned above, these grades are merely distinctions in bean size. And the most famous processing method for Front Street Kenya coffee beans is none other than 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 known as Elephant ear, flat beans with a screen size above 19 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 by an airflow separator C: Screen Size smaller than AB/14 or below, too small to be classified as specialty grade. T: Lighter-weight beans blown out from C grade beans (14 or below) by an airflow separator, meaning both size and density are too small to be classified as specialty grade. PB: Peaberry, meaning round bean, classified not by size but by appearance, unrelated to flavor or weight, accounting for about 10% of total production UG: Those not meeting the above standards

In addition, there is a lower-quality natural sun-dried coffee bean grade, which, due to 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 today's Kenya has long had new concepts for coffee bean grading standards, but the size-based grading standard is still the more common one at present.

Below 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 habitually use a set of "coffee bean quality grading procedures" formulated by Kenyan coffee research institutions, comprehensively grading based on three aspects: green bean quality, roasted bean quality, and cupping quality.

Green bean quality: The judgment items are further subdivided into green bean appearance and size, green bean color, and defects. Roasted bean quality: Subdivided into central crack 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 compiled by Front Street Coffee about Front Street Kenya coffee bean varieties and grading, hoping to help coffee fans who want to understand related knowledge. Next, Front Street Coffee will share the flavor and roasting and brewing data of Front Street Kenya coffee beans.

Front Street Coffee Kenya Small Tomato 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 Roasting Parameters Sharing"

Front Street Kenya Small Tomato Coffee Beans:

This Front Street Kenya Asalia bean has a plump and round body. In order to fully express its bright and full-bodied acidity, Front Street Coffee adopted a light roast level.

Yangjia 800N semi-direct fire, bean charge 480g: charge when the furnace temperature reaches 160°C, open the airflow damper to 3, and set the heat to 120. Turning point: 1'28". When the temperature rises to 130°C, open the airflow damper 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 point; first crack begins at 9'28'', the airflow damper remains unchanged, first crack development time is 2'20'', and the beans are dropped at 193.8°C.

Front Street Kenya Sachini PB Coffee Beans:

This rich Front Street Kenya Sachini coffee bean, due to its higher altitude, has relatively hard bean density, so it climbs at a higher temperature rise at the beginning. The turning point is around 5 minutes, then the heat is lowered to enter the Maillard reaction. At 166°C, the heat is lowered again to extend the Maillard reaction time. When first crack begins, heat absorption is stronger, so it is recommended to maintain heat at this stage to prevent stagnation. First crack development takes more time, which helps reduce acidity and develop flavor.

Roaster Yangjia 800N (roasting capacity 300g), charge at 170°C furnace temperature, heat 100, open airflow damper to 3; turning point at 1'42", when furnace temperature is 140°C open the airflow damper to 3.5, heat unchanged; when furnace temperature is 149°C the bean surface turns yellow, the grassy smell completely disappears, entering the dehydration stage; dehydration is completed at 7'14'', heat and airflow damper unchanged, at 7'30'' wrinkles and dark patches appear on the bean surface, the toast smell turns into coffee aroma, which is 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 the airflow damper to 4, lower heat to 50. After first crack, development time is 1'50'', at 188°C lower heat to 30 to flatten the temperature rise, and drop the beans at 193.3°C.

Front Street Coffee Brewing Suggestions

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

Brewing method: Staged extraction. Use 30g of water for blooming for 30 seconds, pour in a small stream in circles until 124g for the staged pour, and when the water level is about to expose the coffee bed, continue pouring until 228g and stop pouring. When the water level is about to expose the coffee bed, remove the dripper. (Timing starts from the beginning of blooming) Extraction time is 1'55".

Front Street Kenya Small Tomato Coffee Bean Flavor: The wet aroma has ripe tomato and floral notes. On the palate, flavors of cherry tomato and smoked plum, with bright acidity, a clean and rich body, prominent sweetness in the middle, a juicy feel, and a finish of berry notes and yellow sugar sweetness, along with green tea aroma.

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