What is the SL-28 variety?

SL-28 is a Kenyan Arabica variety selected in the 1930s by the Scott Laboratories in Nairobi from a drought-tolerant Tanzanian Bourbon strain. Famous for its wine-blackcurrant-citrus profile and intense tartaric acidity, it has become one of the sensory signatures of Kenyan coffee and one of the most sought-after Arabica varieties in the world.

SL-28's story begins in 1931, when the Scott Agricultural Laboratories in Nairobi, under A. D. Trench, received seeds of a drought-tolerant Tanzanian variety descended from French Bourbon stock. Out of 42 selections tested and labelled SL-1 to SL-42, SL-28 stood out for its acceptable yields and, above all, for the exceptional cup quality it delivered at altitude. A lesser-known sibling often planted alongside it, SL-34, came from a farm near Nairobi (Loresho Estate) and is more productive but slightly less complex. For nearly a century, these two varieties have made up the bulk of Kenya's high-altitude plantings, alongside Ruiru 11 (1985) and Batian (2010).

The cup profile of a well-processed Kenyan SL-28 (Kenyan-wash double fermentation, altitude 1,700-2,000 m, phosphorus-rich volcanic soils) is instantly recognisable: very intense tartaric acidity, occasionally almost 'wine-like', dominant notes of blackcurrant, ripe tomato, pink grapefruit, cranberry, rhubarb, with a dense, syrupy body and a long retro-olfaction. Top lots from Nyeri, Kirinyaga or Kiambu reach 88 to 92 SCA points. That signature has given SL-28 near-iconic status in the third wave: on roasters' menus in London, Copenhagen or Berlin, a 'Nyeri SL-28 AA washed' is often one of the most scrutinised listings.

The variety remains relatively low-yielding, susceptible to leaf rust and to coffee berry disease (CBD). Since the 1990s, Kenya's Coffee Research Institute has pushed growers to partially replace it with Ruiru 11 and Batian, which are hardier but carry less prestige. SL-28 has also travelled: it is now grown in Uganda, Rwanda, Burundi, and in Central America (Costa Rica, Panama, El Salvador) under the 'SL-28' label or sometimes relabelled locally. For Belgian specialty roasters — Brussels, Ghent, Antwerp, Liège — a Nyeri SL-28 remains a flagship on the single-origin menu, best served as filter to preserve its acid structure, far from the chocolatey profile the Belgian speculoos-and-filter tradition has favoured.

SL-28 — variety sheet