SL28 and SL34

The SL28 and SL34 cultivars were developed by Scott Agricultural Laboratories (SAL) in Kenya during the 1930s and 1940s. The 'SL' designation refers to the laboratory itself, which operated out of a former sanatorium in Kikuyu. These varieties were the result of rigorous single-tree selection programs aimed at identifying plants that could thrive in the specific environmental conditions of the Kenyan highlands while delivering superior sensory attributes. While they were initially intended to improve agricultural output, their enduring legacy is defined by their remarkable flavor potential rather than their productivity.

SL28 is widely considered to be of the Bourbon genetic group. It was selected from a population identified as 'Tanganyika Drought Resistant' and was specifically prized for its ability to withstand water scarcity through a deep root structure. Despite its lower yields and susceptibility to major diseases like coffee leaf rust and coffee berry disease, it remains one of the most highly regarded varieties in Africa due to its profound sweetness, balance, and complex acidity.

SL34, by contrast, is often associated with a Typica-like genetic background. It was selected from a single tree on the Loresho Estate in Kabete, Kenya, which was labeled as 'French Mission'—a term historically used for Bourbon-related trees. SL34 is generally more productive than SL28 and demonstrates better adaptability to varying altitudes and sudden heavy rainfall. While it shares the same disease vulnerabilities as its sibling, its ability to perform across a wider range of elevations has made it a staple for many smallholder farmers.

In the field, both plants are tall, large-beaned Arabica varieties. They are frequently intercropped on small 'shamba' farms alongside food crops, often at high altitudes ranging from 1,800 to 1,900 meters. Their bronze-tipped new growth is a common visual identifier. Because they are non-hybrid, they require careful management, as they lack the genetic resistance to modern coffee pathogens that newer, bred varieties like Ruiru 11 or Batian possess.

For the roaster and the drinker, these cultivars are synonymous with the quintessential Kenyan cup profile. They are celebrated for a vibrant, juicy acidity and distinct flavor notes, most notably blackcurrant, black plum, and tomato. While they are distinct in their genetic origins and agronomic performance, they are frequently blended in production, contributing to the consistent, high-intensity character that defines the region's specialty coffee exports.

Producers continue to cultivate SL28 and SL34 because of their unmatched market value and sensory reputation. Even as research institutes have introduced disease-resistant hybrids, these classic selections remain the benchmark against which other varieties are measured. Their presence in the landscape is a testament to the success of early 20th-century selection programs, which prioritized the preservation of high-quality genetic traits that continue to command premium prices in the global specialty market today.