SL-28 Coffee Variety: A Kenyan-Bred Icon of Cup Quality and Resilience

1. Origin and Development

SL-28 is one of the most celebrated and genetically influential Arabica coffee varieties in the world. It was developed in Kenya in the 1930s by the Scott Agricultural Laboratories (hence the prefix “SL”), a colonial-era research institution tasked with identifying and cultivating high-performing coffee varieties for East Africa.

SL-28 was selected from a Tanganyika (now Tanzania) drought-resistant Bourbon-type variety and was formally cataloged in 1935. The goal was to find a cultivar that could thrive under low rainfall conditions while producing excellent cup quality—a balance of resilience and sensory excellence.

2. Botanical Classification and Traits

Species: Coffea arabica
Genetic Lineage: Bourbon-related (but genetically distinct from Typica)
Plant Type: Tall, with broad, bronze-tipped leaves
Maturity: Medium-late ripening
Leaf rust resistance: Low
Drought resistance: High
Yield potential: Moderate to low (especially compared to modern hybrids)
Bean size: Medium to large
SL-28 is prized for its deep root system, which enables the plant to withstand longer dry seasons. However, it is susceptible to diseases such as Coffee Leaf Rust (CLR) and Coffee Berry Disease (CBD)—a major reason why many farmers in Kenya and beyond have moved toward hybrid varieties with better resistance.

3. Cup Profile and Sensory Quality

The SL-28 variety is renowned for its extraordinary cup quality, particularly when grown at elevations above 1,500 meters. Its hallmark attributes include:

Lively, citric acidity (often compared to blackcurrant or lemon)
Juicy and syrupy body
Complex fruit notes (tropical fruit, red berries, stone fruit)
Sweetness reminiscent of brown sugar or caramel
Wine-like structure and vibrant clarity
When properly processed—especially through washed or double-washed methods—SL-28 consistently delivers high cupping scores and is a frequent selection in Cup of Excellence competitions and barista championships.

4. Geographic Cultivation

Though developed in Kenya, SL-28 has been planted in other highland regions with success, including:

Tanzania
Uganda
Malawi
Rwanda
Burundi
Colombia (in select micro-lots)
Panama and Costa Rica (experimental and high-end farms)
In Kenya, SL-28 and its sibling SL-34 are still common in older farms and cooperatives. Many producers today use field blends of SL-28, SL-34, and Ruiru 11 or Batian—newer, disease-resistant hybrids.

5. Relationship to SL-34 and Other SL Varieties

SL-28 is often mentioned alongside SL-34, another cultivar selected by Scott Labs. While both share Bourbon ancestry and are prized for flavor, SL-34 has better resistance to leaf rust but lower drought tolerance.

Other SL lines, such as SL-14 and SL-39, were also part of the same breeding program, but SL-28 stands out as the most globally recognized and widely appreciated for cup quality.

6. Role in Specialty Coffee and Value Chain

In the world of specialty coffee, SL-28 is a marquee variety, often used as a benchmark for origin character and flavor intensity. Its prominence has led to:

Premium pricing at origin, especially in Kenya and Ethiopia
Direct trade relationships centered on SL-28 microlots
Showcasing in competitions and limited-edition releases
However, its low disease resistance and lower yield make it a risky economic choice for smallholders, especially in an era of climate change and pest pressure. As a result, SL-28 is increasingly reserved for high-elevation farms and premium markets where price premiums justify the risks.

SL-28 remains one of the most revered cultivars in specialty coffee—valued not just for its history and genetics, but for the consistently dazzling cup experience it provides. While its cultivation requires careful management and may not offer the same yields as modern hybrids, its sensory rewards and iconic status ensure it will remain a staple of top-tier coffee programs for years to come.