SL28 and SL34: The Varieties Behind Kenya's Famous Cup
Two Lab Codes Worth Knowing
Kenyan coffee is known for intense, juicy acidity and flavors like blackcurrant, grapefruit and tomato. A big part of that comes from two varieties with plain names: SL28 and SL34. “SL” stands for Scott Agricultural Laboratories, the research station in Kenya where they were selected in the 1930s. The number is simply the label of the selection.
If a bag lists “SL28, SL34”, you are holding the classic Kenyan profile. This guide explains where they came from, how they differ, and what else you may see next to them.
Selected at Scott Labs
In the 1930s, Kenya was a British colony, and Scott Agricultural Laboratories (today Kenya’s National Agricultural Research Laboratories) worked with estate owners to find coffee trees suited to local farms. Researchers picked single, promising trees and multiplied them.
- SL28 was selected in 1935 from a single tree in a population called “Tanganyika Drought Resistant”, traced to the Moduli district of what is now Tanzania. Scott Labs confirmed it handled drought well. Genetic tests show SL28 is related to the Bourbon lineage.
- SL34 was selected in the late 1930s from a single tree on the Loresho Estate in Kabete, near Nairobi. The tree was labeled “French Mission”, a name linked to missionaries who planted Bourbon seed from Réunion in Kenya in 1893. But genetic tests now show SL34 is related to the Typica lineage, so the label story may be wrong.
So the two Kenyan classics come from the two great Arabica family lines: SL28 from Bourbon, SL34 from Typica.
SL28 vs SL34
| Trait | SL28 | SL34 |
|---|---|---|
| Lineage | Bourbon-related | Typica-related |
| Height | Tall | Tall, with bronze leaf tips |
| Yield | Low | Very high |
| Drought | Tolerant | Suited to areas with good rainfall |
| Leaf rust | Susceptible | Susceptible |
| Coffee berry disease | Susceptible | Highly susceptible |
| Best altitude | Above about 3,900 ft (1,200 m) near the equator | Same; adapted to high areas |
| Cup quality | Exceptional at high altitude | Exceptional at high altitude |
| Main countries | Kenya, Uganda, Malawi, Zimbabwe | Mostly Kenya |
Source: World Coffee Research variety catalog.
SL28 is also known for being tough: an SL28 tree can survive long periods without care and then return to production. That is part of why it spread beyond Kenya, especially to Uganda’s Arabica regions, and more recently to some farms in Latin America.
The Disease Problem and the Newer Varieties
Both SL varieties are vulnerable to coffee berry disease (CBD), a fungus that attacks the green cherries, and to leaf rust. To fight this, Kenyan researchers bred new varieties:
- Ruiru 11 (released in the 1980s): a compact, high-yielding, disease-resistant cross whose parents include SL28 and SL34, plus Timor Hybrid for resistance.
- Batian (released in 2010): a tall selection from Ruiru 11 stock, chosen for disease resistance and cup quality closer to the SL varieties.
Most Kenyan lots are a mix of whatever a cooperative’s members grow, so labels like “SL28, SL34, Ruiru 11, Batian” are common. Some coffee buyers prefer pure SL lots for cup quality; others find good Batian very close.
What It Tastes Like
Kenyan SL coffees are among the most distinctive in the world. Typical notes:
- Blackcurrant, blackberry or red currant
- Grapefruit, lime or other citrus
- Tomato or savory, sweet-sour notes
- High, juicy acidity and a syrupy body
Some drinkers find SL28 a touch more complex and SL34 a little heavier, but most bags blend them, and the farm, processing and altitude matter at least as much.
Reading a Kenyan Bag
You will often see three kinds of information:
- Variety: “SL28, SL34” alone, or with Ruiru 11 and Batian.
- Grade: AA and AB are bean-size grades (AA is largest). Size is not the same as flavor; a great AB can beat an average AA.
- Place: the county (Nyeri, Kirinyaga, Embu, Murang’a, Kiambu) and the factory, which in Kenya means the washing station.
Tip: Kenyan coffees are usually washed. If you see a natural Kenyan, expect it to taste quite different.
Kenyan SL coffees generally cost somewhat more than an average single-origin from the same roaster, reflecting strong demand and Kenya’s auction system. A pure SL28 lot from a named factory often sits at the higher end. See our buying guide for picking a roaster.
Best Roast and Brew
- Roast: light to light-medium. Darker roasts flatten the fruit and acidity that make Kenyan coffee special.
- Brew: pour-over at 15 g coffee to 250 g water (1:16) and about 205 °F (96 °C). Let it cool a little; the fruit gets sweeter.
- Process: washed is the classic. Our processing guide explains why it tastes so clean.
If you want to know what “bright” coffee really means, buy one washed Kenya SL28/SL34 and brew it as a light-roast pour-over. It is unforgettable, and it will reset what you expect from a cup.