SL28 / SL34

Arabica varieties selected in Kenya by Scott Agricultural Laboratories (1931-1935) from Tanzanian Bourbon. SL28: large bean, intense phosphoric acidity, blackcurrant notes. SL34: resistant to heavy rains, similar profile. Icons of Kenyan specialty coffee, now also planted in Colombia and Panama.

Background & Context

SL28 and SL34 are the two most important specialty coffee varieties selected by Scott Agricultural Laboratories (SL) in Kenya during the 1930s — both selections that have come to define the "Kenyan coffee" profile known internationally. SL28 was selected in 1935 from Loresho Estate material, believed to be derived from drought-resistant Tanganyika material; SL34 was selected in 1935 from the Loresho Estate's "French Mission Bourbon" lineage — making SL34 a Bourbon descendant rather than SL28's drought-resistant origin. The two varieties produce distinct but complementary cup profiles: SL28 is associated with the most intense blackcurrant and cassis acidity; SL34 with more complex fruit (mango, tropical fruit, some blackcurrant) and heavier body. Many of Kenya's finest lots from the top cooperatives (Nyeri's Tegu, Kirinyaga's Kiamabara, Kiambu's Ndumberi) are either pure SL28 or SL28/SL34 blends.

Practical Use

For buyers and roasters working with Kenyan coffee, the SL28/SL34 distinction provides useful quality and flavour prediction. Pure SL28 lots from above 1,700m — particularly from Nyeri and Kiambu cooperatives — produce the most dramatic blackcurrant and cassis intensity. SL34 adds complexity and body but slightly mutes SL28's characteristic sharpness, making SL28/SL34 blended lots from cooperatives often more espresso-friendly than pure SL28 at light roast. Both varieties are susceptible to coffee leaf rust, which has driven Kenya's coffee research institute (KALRO) to develop rust-resistant hybrids — but early hybrids sacrificed cup quality, and KALRO is now working on genetics that maintain SL28/SL34 quality in rust-resistant backgrounds. The SL28/SL34 combination also creates a practical cupping benchmark for Kenyan origin training: the contrast between pure SL28 (maximum cassis intensity) and SL34-dominant lots (tropical fruit, softer acidity) allows tasters to develop a sensory reference for how variety within the same origin and process can produce meaningfully different cups. This varietal distinction within a single origin is one of the most compelling arguments for variety-level traceability in specialty sourcing — and one that Kenyan producers and cooperatives increasingly provide in their lot documentation.

Related Terms

Related terms: SL28, SL34, Kenya coffee, Bourbon, Acidity.