The Scott Labs Experiment
In the early 1930s, Scott Agricultural Laboratories in Kenya began a systematic project to identify and propagate the most productive and disease-resistant coffee cultivars for Kenyan growing conditions. They collected samples from across the country and assigned each a sequential number.
Selection 28 — later known as SL-28 — came from a drought-resistant variety found in the Tanganyika (now Tanzania) region. It was chosen primarily for its resilience, not its taste. The researchers had no way of knowing they had selected what would become one of the most celebrated flavor profiles in coffee history.
What Makes SL-28 Special
SL-28 produces a cup profile that is almost unmistakable to anyone who has tasted it: intense blackcurrant, bright citric acidity (often compared to grapefruit or blood orange), and a savory depth that can read as tomato or red wine depending on the lot.
This intensity comes from the cultivar's genetic heritage and the terroir of the Kenyan highlands. SL-28 grows best at 1,400-2,000 meters on the volcanic soils around Mount Kenya, Nyeri, and Kiambu. The combination of high altitude, red volcanic soil, and equatorial climate creates the slow cherry maturation that develops complex sugars and acids.
The Processing Factor
Kenya predominantly uses washed (fully washed) processing with an extended fermentation stage — typically 24-72 hours, sometimes longer. This extended fermentation is unusual by global standards and is partly responsible for the distinctive brightness and complexity of Kenyan coffees.
After fermentation, beans are soaked in clean water for another 12-24 hours, then dried on raised beds. This meticulous, labor-intensive process contributes to Kenya's position at the premium end of the global coffee market.
SL-28 vs SL-34
SL-34, the other famous Kenyan cultivar from the same Scott Labs project, shares some similarities but tends toward heavier body and more subdued acidity. Most Kenyan lots are blends of SL-28 and SL-34 from the same farm, though some specialty roasters now offer single-cultivar lots.
The practical difference: SL-28 dominates when you want bright, fruity complexity. SL-34 contributes body and sweetness. Together, they create the classic "Kenyan" profile that has defined East African specialty coffee.
Growing SL-28 Outside Kenya
In recent years, farmers in Colombia, Guatemala, and even Hawaii have planted SL-28. The results are interesting but different — the cultivar expresses differently in each terroir. Colombian SL-28 tends toward tropical fruit rather than blackcurrant. Guatemalan SL-28 develops more chocolate and red fruit.
This is a reminder that cup quality is a function of cultivar and environment, not cultivar alone.
How to Brew SL-28
SL-28 coffees reward bright, clean extraction methods. Pour over at a 1:16 ratio highlights the acidity and complexity. Espresso works well too — expect a juicy, fruit-forward shot at a 1:2.5 ratio with 93-94C water.
Read the full SL-28 bean profile for detailed tasting notes and recommended pairings.