What Is SL28 — the Legendary Variety That Defines Kenya
The truth behind the blackcurrant acidity, its origin and its difficulty to grow
That "acidity" in Kenyan coffee comes from the variety. SL28 and SL34, selected by Scott Laboratories in the 1930s. Drought-tolerant, yet low-yielding and disease-prone. We read why it endures from the variety's history.
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If you have ever drunk a Kenyan specialty and felt "blackcurrant, cassis, tomato-like," you have almost certainly met the variety SL28. Selected in the 1930s at Scott Laboratories on the outskirts of Nairobi, it is the driving force that put Kenyan coffee at the top of the world.
The background of the selection: in search of a drought-tolerant variety
Back in the 1930s, Kenya's large farms were plagued by severe drought. The colonial government commissioned Scott Laboratories to develop a drought-tolerant variety. From landraces brought in from Tanzania they selected promising individuals and managed them by number as the SL (Scott Labs) lines. SL28 was the individual among them that showed the brightest acidity and the most complex aroma.
The difference between SL28 and SL34
- SL28: altitude 1,500–2,100m, secures water with deep roots, strong blackcurrant acidity
- SL34: strong in areas with heavy rainy seasons, a slightly gentler acidity than SL28
- Both carry Bourbon-line genetic traits and make Kenya's "that taste"
If you get hold of a single SL28 lot, avoid a dark roast. A light-medium to medium roast brings out the blackcurrant acidity most clearly.
The price of being hard to grow
SL28 is weak against rust (coffee leaf rust) and yields less than newer varieties. Commercially, disease-resistant hybrids like Ruiru 11 and Batian are more rational. That Kenyan farmers keep growing SL28 anyway is because the market pays a premium for "that acidity." It is a textbook example of the quality-versus-efficiency trade-off shown through variety choice.
How to try SL28
Top lots of Kenya AA and peaberry, especially single-co-op lots from Nyeri/Kirinyaga/Murang'a, are candidates with a high SL28 ratio. Specialty roasters sometimes carry lots marked "100% SL28," and that is the clearest gateway.
Basic ratio for brewing with a V60 (1:16)
Beans 15g / Water 240g
Water at 90–92°C is recommended. Above 94°C the acidity turns too aggressive and crushes SL28's delicate aroma. With a medium-speed drip that drains out at 3:00, enjoy the sweetness that rises as it cools.
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