SL28 and SL34: Kenya's Famous Varieties

SL28 and SL34 are two arabica varieties selected in Kenya in the 1930s by Scott Agricultural Laboratories, a colonial-era research station. Both remain closely tied to Kenya's international reputation for bright, intense coffee, even though neither variety resists the country's major coffee diseases well.

Where did SL28 and SL34 come from?

Both varieties trace back to tree-selection work carried out at Scott Agricultural Laboratories, later Scott Laboratories Kenya, in the 1930s. SL28 was selected in 1935 from a single tree within a population called Tanganyika Drought Resistant, after the lab's senior coffee officer, A.D. Trench, collected seed from Tanzania's Moduli district in 1931 for its drought tolerance, according to World Coffee Research. SL34 came from a separate single-tree selection made on the Loresho Estate in Kabete, Kenya, from a tree labeled "French Mission" — a nod to coffee that French Catholic missionaries had brought to East Africa — as part of the same wave of "SL"-prefixed selections made between 1935 and 1939.

What is the genetic relationship between SL28 and SL34?

The two varieties turn out to be less closely related than their shared "SL" prefix and Kenyan origin suggest. World Coffee Research classifies SL28 as having a Bourbon-like genetic background, while genetic testing places SL34 in the Typica genetic group instead — despite SL34's "French Mission" label, which is more commonly associated with Bourbon-lineage coffee introduced elsewhere in East Africa. In practice, both are grown and marketed together as Kenya's signature named varieties, regardless of which side of the Bourbon-Typica family tree each one falls on.

Where are SL28 and SL34 grown today?

SL28 is found commonly in Kenya, Malawi, Uganda and Zimbabwe, and in recent decades it has also been planted experimentally in parts of Latin America by growers chasing its cup reputation. World Coffee Research notes that SL34, by contrast, is found mostly in Kenya itself, with less of a footprint elsewhere.

What are SL28 and SL34's plant traits and disease resistance?

Neither variety offers much protection against coffee leaf rust, and SL34 is rated highly susceptible to coffee berry disease as well — real vulnerabilities in a country that has battled both diseases for decades. SL28's drought tolerance, inherited from its Tanganyika Drought Resistant ancestry, is its one clear agronomic advantage over SL34.

What do SL28 and SL34 coffee taste like?

World Coffee Research rates both varieties' quality potential as "Exceptional" at high altitude, the catalog's top rating, and both are closely associated with Kenya's reputation for vivid, wine-like acidity and blackcurrant character. Roasters do not always distinguish sharply between the two in cupping notes, since most Kenyan lots blend trees of both varieties, but SL28 is more often singled out by name as the variety most responsible for that distinctive Kenyan profile.

How do growers and buyers use SL28 and SL34?

For Kenyan growers, SL28 and SL34 remain the traditional benchmark against which newer, more disease-resistant varieties like Ruiru 11 and Batian are judged — valued for cup quality despite needing more active disease management to stay productive. For buyers, seeing "SL28" or "SL34" named on a Kenyan bag is generally read as a signal of traditional Kenyan character, distinct from the newer hybrid varieties bred more for yield and disease resistance than for cup score; readers can see how the two fit alongside Kenya's grading system on the Kenyan coffee guide.

How do SL28 and SL34 compare with Jamaica Blue Mountain?

SL28 and SL34 sit closer to Jamaica Blue Mountain than most modern varieties in one specific respect: like Blue Mountain's Typica, neither offers much natural disease resistance, and both were selected primarily for cup quality rather than yield. Where they diverge sharply is in flavor. Blue Mountain is consistently described as mild and balanced with low bitterness, while SL28 and SL34 are the backbone of Kenya's much brighter, more acid-forward, blackcurrant-toned reputation — arguably the most intense-cupping counterpoint to Blue Mountain's restraint among the world's well-known named varieties.