SL28

What SL stands for

Sourced

SL stands for Scott Laboratories, the colonial-era agricultural research station in Kenya now known as the National Agricultural Laboratories. In the 1930s it made a series of individual tree selections, each given a number. SL28 and SL34 are the two that became widely planted.

According to the catalogue, SL28 was selected in 1935 from a single tree in a population known as Tanganyika Drought Resistant, and has a Bourbon-like genetic background.

Strengths and weaknesses on the farm

Sourced

As listed in the World Coffee Research catalogue. The catalogue notes it is found commonly in Kenya, Malawi, Uganda and Zimbabwe.

A tree that lasts

Sourced

The catalogue records that there are SL28 trees in many parts of Kenya that are sixty to eighty years old and still productive, and describes the variety as notably rustic: able to tolerate neglect and low inputs. That hardiness, together with drought tolerance and a low demand for nutrients, explains why it has stayed in the ground despite its disease problems.

The same character shows in how it is planted. The catalogue gives a density of only 1,000 to 2,000 trees per hectare, a fraction of what compact varieties are grown at, because a large, long-lived tree needs room. Fewer trees on the land is one reason the yield per hectare is low even when each tree is healthy.

The disease problem, and Kenya's answer

CoffeeHQ explanation

Coffee berry disease and leaf rust are both serious in Kenya, and SL28 resists neither. Growing it well depends on spraying, which costs money that smallholders often do not have. Kenyan breeders therefore developed resistant varieties, Ruiru 11 and later Batian, intended to match the cup quality of the SL selections without the losses.

Whether they do match it is argued over in the trade. Many buyers still pay more for lots that are predominantly SL28 and SL34, and many Kenyan lots are a mixture of all of them.

The cup it is known for

Tendency, not a guarantee

Kenyan coffees built on SL28 are widely described as intensely fruity with pronounced, juicy acidity, often compared to blackcurrant. That reputation belongs to a combination of variety, high altitude, soils and Kenya's characteristic washed processing with extended soaking, and it is not possible to say how much is the variety alone.

SL28 is now planted in Latin America too, where it produces coffees that are recognisably related but not the same, which is itself a demonstration of how much place and process contribute.

What to do next

• Coffee from Kenya — The origin, its regions and the processing that goes with the variety.
• SL34 — The sister selection, usually grown and sold alongside it.
• The washed process — The method behind the clean, bright Kenyan style.
• Become a coffee expert — A structured programme from the plant and its processing to roasting, water and tasting.