Difference Between SL28 and SL34: Kenya’s Famous Coffee Varieties

Pick up a bag of Kenyan coffee and the label almost always reads “SL28, SL34” as if the two were a single thing. They are not. The short answer to the difference between SL28 and SL34: SL28 is a drought-tolerant, Bourbon-related selection traced to seed from Tanganyika (today’s Tanzania), while SL34 came from a single tree on an estate near Nairobi and turns out, genetically, to be Typica-related. Both are tall, large-beaned and prized for quality, and both are vulnerable to the diseases that now push Kenyan farmers toward newer varieties.

Below you will find where the letters come from, how each variety behaves on the farm, what roasters tend to taste in the cup, and how to read a Kenyan label that lists them together.

Key takeaways

• “SL” stands for Scott Laboratories, the Kenyan government lab (now NARL at Kabete) that selected both varieties in the 1930s.
• SL28 is Bourbon-related and drought tolerant; SL34 is Typica-related and suited to wetter, high-altitude farms.
• Both have large beans and excellent quality potential at altitude, but both are susceptible to coffee berry disease and leaf rust.
• Ruiru 11 (1985) and Batian (2010) were bred in Kenya partly from SL28 and SL34 to resist those diseases.
• Most Kenyan lots are field blends, so the cup reflects farm, altitude and processing as much as variety.

In this article

1. What does SL stand for?
2. The difference between SL28 and SL34
3. How they behave on the farm
4. What they taste like
5. Ruiru 11 and Batian: the next generation
6. FAQ

What does SL stand for in SL28 and SL34?

SL is short for Scott Laboratories, more fully Scott Agricultural Laboratories, a research station set up by the colonial government in Kenya. It still exists as the National Agricultural Research Laboratories (NARL) at Kabete, outside Nairobi. In the 1930s its agronomists collected promising coffee trees, numbered each selection, and tested them for yield, drought response and cup quality. Most of the numbered selections faded away. Two did not.

The number is simply the selection’s catalogue number. There is no hidden meaning in 28 or 34, and the gap between them does not mean one is an “upgrade” of the other. They are separate single-tree selections from different source populations.

The difference between SL28 and SL34, side by side

The clearest way to see how the two differ is to put the documented traits next to each other. The data below comes from World Coffee Research’s variety catalogue, the reference most roasters and agronomists use.

The surprise in that table is the genetic group. Because SL34’s parent tree carried the French Mission label, people assumed for decades that it was a Bourbon, like the coffee French missionaries brought to East Africa. Genetic testing reported by World Coffee Research places it with Typica instead. Nobody has fully explained the mismatch: the original tree may have been mislabelled, or Typica material may have mixed into the French Mission population.

How SL28 and SL34 behave on the farm

SL28: the survivor

SL28 was picked for its ability to cope with dry spells, and it has a reputation for toughness. World Coffee Research notes that Kenyan SL28 trees 60 to 80 years old are still productive, and that neglected trees can recover and crop well again. Its weakness is output: yields are low, so farmers trade volume for quality. Its branches start semi-erect and droop after several harvests.

SL34: the high-rainfall specialist

SL34 suits higher, wetter farms. It gives more coffee per tree than SL28, but its high susceptibility to coffee berry disease is a real problem in exactly the damp conditions where it grows best. Farmers either spray, accept losses, or graft and replant with resistant varieties.

The shared weakness

Neither variety resists coffee leaf rust or coffee berry disease, and SL28 is also vulnerable to root-knot nematodes. That is the main reason their share of Kenyan planting has been under pressure, even as specialty buyers keep asking for them by name.

SL28 vs SL34: what do they taste like?

Roasters often describe Kenyan coffees from these varieties as bright and juicy, with blackcurrant, red fruit, citrus and a winey acidity. SL28 is usually credited with the more intense, sparkling acidity; SL34 is often described as slightly heavier in body. Treat those as tendencies, not rules. In practice:

• Most lots are field blends. Kenyan smallholders deliver cherry to a shared washing station, so a lot labelled “SL28, SL34” is a mix you cannot taste apart.
• Processing shapes the cup. Kenya’s classic method is fully washed, often with an extra soak, then drying on raised beds. That style tends to make acidity cleaner and brighter. Our guide to coffee processing methods explains why.
• Altitude matters most. Both varieties only show their best above roughly 1,200 m near the equator, which is where most Kenyan specialty coffee grows.

If you want to taste the style yourself, brew it black, slightly lighter than you would a Brazil or Sumatra, and let it cool a few degrees: the fruit notes open up as the cup drops toward drinking temperature.

Ruiru 11 and Batian: why newer varieties sit beside SL28 and SL34

Kenya’s Coffee Research Institute at Ruiru spent decades breeding around the weaknesses of its famous selections. Ruiru 11, released in 1985, is a compact, disease-resistant variety. Batian, released in 2010, is taller and resistant to coffee berry disease with intermediate resistance to leaf rust; its ancestry includes SL28 and SL34 along with Rume Sudan and Timor Hybrid lines. That is why modern Kenyan labels often read “SL28, SL34, Ruiru 11, Batian”: farmers plant resistant trees alongside the classics to protect their harvest.

How to read a Kenyan label

• “SL28” alone: a single-variety lot, usually from an estate. Rare and often priced higher.
• “SL28, SL34”: the classic field blend from smallholders.
• “SL28, SL34, Ruiru 11, Batian”: a modern washing-station blend. Not a lesser coffee; quality depends on the farms and processing.
• AA, AB, PB: bean size grades, not varieties. Our guide to coffee grades covers them.

Taste SL28 and SL34 at home

Our Kenya single origin comes from Othaya in Nyeri County, grown at 1,700 to 1,890 m from SL28, SL34, Ruiru 11 and Batian, fully washed and dried on raised beds: a textbook modern Kenyan blend with orange, lemon and floral notes. For the same bright East African character in a darker, espresso-friendly roast, try African Espresso, which blends Kenya, Tanzania and Ethiopia, or browse all our single origins. Every bag is roasted 1 to 5 days before it ships.

SL28 and SL34 FAQ

Is SL28 a Bourbon?

SL28 is Bourbon-related. It was selected from a Tanganyikan population with a Bourbon-like genetic background, so it is often grouped with Bourbon types.

Is SL34 a Bourbon or a Typica?

Genetic testing places SL34 in the Typica-related group, despite its parent tree being labelled French Mission, a name usually linked to Bourbon.

Is SL28 grown outside Kenya?

Yes. World Coffee Research lists it as common in Kenya, Malawi, Uganda and Zimbabwe, and it has also been planted in Latin America.

Which is better, SL28 or SL34?

Neither is objectively better. SL28 is often linked to brighter acidity and SL34 to fuller body, but farm, altitude and processing usually matter more than the variety name.

Why are SL28 and SL34 always listed together?

Because Kenyan smallholders grow them side by side and deliver cherry to shared washing stations, so most lots are field blends of both.

Sources

1. SL28 variety profile, World Coffee Research, Arabica Coffee Varieties catalogue.
2. SL34 coffee varietal, Ozone Coffee, summarizing World Coffee Research data.
3. Batian coffee varietal, Ozone Coffee, citing Kenya’s Coffee Research Institute.

Facts checked in October 2026.

Keep reading: Kenyan coffee guide · Coffee varieties explained · Single origins