Kenya ranks as the 16th largest coffee producer globally and stands out as a major origin for specialty coffee. The country’s central highlands, with their nutrient-rich, acidic soil and ideal climate, create perfect conditions for cultivating high-quality Kenyan coffee.
Known for its vibrant acidity, full-bodied richness, and unique flavor profiles, Kenyan coffee is celebrated worldwide. Some of the most well-known varieties include K7, Blue Mountain, Batian, Ruiru 11, and the famous SL series.
The SL series, in particular, has been a cornerstone of Kenyan coffee farming for nearly 90 years. While it includes several varieties, SL-28 and SL-34 are among the most renowned. Despite the rise of new hybrids and disease-resistant varieties, SL-28 and SL-34 remain favored by many Kenyan coffee farmers for their robust yields, longevity, and exceptional cup quality.
To delve deeper into these beloved varieties, I spoke with professionals in the Kenyan coffee industry. Keep reading to discover their insights on what makes these coffees so special.
What Are the SL-28 & SL-34 Varieties?
If you’ve ever enjoyed a cup of Kenyan coffee, chances are it was made from an SL-series plant. “SL” stands for Scott Laboratories, the Kenyan research center responsible for developing these varieties in the 1930s. Among the SL varieties, SL-28 and SL-34 are the most famous in the world of specialty coffee.
While SL-28 has spread to parts of Latin America, these varieties are still most commonly found in Kenya, where they are almost synonymous with Kenyan coffee production. Francis Mwangi, who has been farming SL varieties for over 30 years, is a self-proclaimed SL expert. He believes that these varieties will “always be the best,” praising their incredible yields. “With proper care, the SL varieties give back in abundance,” he says, noting that it’s not uncommon to get over 10kg of coffee cherries per plant without requiring the intensive attention that some other varieties, like Ruiru 11, need.
SL-28 trees are known for their tall stature, green-tipped leaves, and high yields. They are drought-resistant and have excellent cup quality, though they are vulnerable to coffee leaf rust, coffee berry disease (CBD), and soil nematodes. These trees begin producing large cherries after about three years, and when well-maintained, they have a low milling loss, meaning a higher proportion of green coffee beans.
SL-34 trees, in comparison, are structurally similar but can be recognized by their dark bronze leaf tips. They require more nutrition than SL-28 and have slightly lower yields, but share the same susceptibility to pests and diseases.
The SL series has been cultivated in Kenya for decades, and it’s estimated that up to 80% of all exported Kenyan coffee is from SL varieties. Despite their vulnerability to pests, Francis explains that SL varieties are hardy and can continue to produce, even after years of neglect. “Once you start caring for them again, they bounce back like they were never abandoned,” he says.
In the world of Kenyan coffee, the SL varieties remain celebrated for their resilience, longevity, and exceptional quality, making them a staple of the country’s coffee industry for generations.
Cup Profile of Kenyan Coffee: SL-28 & SL-34
When grown at medium to high altitudes—typically 700 meters above sea level and higher—SL varieties ripen slowly, resulting in exceptional, high-quality coffees. These beans produce a rich, full-bodied cup with vibrant acidity and distinct nutty, fruity flavors.
David Mathenge, a Kenyan coffee grader (known locally as a “liquorer”), notes that SL-variety beans often release a “floral and spicy” aroma when ground. “The cup is so full-bodied, you can feel it immediately,” he says. David believes that if a more disease-resistant SL cultivar had been developed, the Kenyan coffee industry would be operating at an entirely different level today.
While newer varieties like Batian and Ruiru 11 continue to grow in popularity, SL-28 and SL-34 are still celebrated for their consistently high cup quality. David remarks that these SL varieties offer a complexity that many modern cultivars can’t quite match, which may explain their lasting presence in the Kenyan coffee landscape.
“The SL varieties just have that ‘X factor’ tasters are always looking for,” he explains. Although newer varieties are adapting to Kenyan soil and climate, SL varieties remain the gold standard in the country’s coffee production.
David also points out that most Kenyan coffee varieties still come from the SL series, and they often receive high ratings. The primary defects observed in these coffees usually stem from insect damage or disease, but otherwise, their large cherries fetch good prices for farmers, making SL varieties a valuable asset to the Kenyan coffee industry.
Will SL-28 & SL-34 Remain Popular in Kenyan Coffee?
Although SL-28 and SL-34 are widely grown across Kenya, they present significant challenges for farmers. As mentioned earlier, both varieties are highly susceptible to coffee leaf rust, coffee berry disease (CBD), and nematodes. These threats can devastate entire crops, leaving many farmers vulnerable. Joseph Wambugu, a prominent Kenyan coffee producer, recalls the damage caused by CBD just a few years ago: “I lost around half my crop, and many other farmers lost everything.”
Fortunately, Joseph’s Ruiru 11 plants were resilient enough to recover, but others weren’t as fortunate. To manage the risks associated with SL varieties, farmers must invest heavily in pest and disease control. Joseph explains that while these varieties deliver high yields, much of the profit is reinvested into maintaining the crops. Farmers must follow strict seasonal programs to combat coffee leaf rust and CBD, but this is both costly and labor-intensive.
As a result, more farmers are turning to newer Kenyan coffee varieties like Batian and Ruiru 11, which offer greater resistance to diseases and pests. These newer varieties are easier and less expensive to cultivate, making them more appealing to producers. Some farmers are even converting their SL crops by grafting these resilient varieties onto SL rootstock.
However, despite this shift, Joseph believes the SL varieties will remain a fixture in Kenyan coffee for years to come. “Even though these new varieties are better at resisting disease, the SLs are still so widely planted that they won’t disappear overnight,” he says.
Furthermore, the SL varieties continue to play a crucial role in breeding new cultivars or serving as rootstock for grafting. As breeders develop more resilient plants based on SL genetics, the influence of SL-28 and SL-34 will persist in Kenyan coffee for decades to come. With future innovations, we may even see a “descendant” of the SL series that combines the best traits of both worlds: excellent cup quality and increased resistance to pests and diseases.
Currently, the standout qualities of the SL varieties are their impressive yields and exceptional cup profile. Despite the challenges they pose in cultivation, these traits ensure that SL-28 and SL-34 remain a viable—though somewhat risky—choice for many farmers.
Kenyan coffee enthusiasts around the globe continue to recognize and appreciate the distinctive flavors these varieties offer, making them highly sought after by both consumers and roasters. It’s clear that the demand for SL-28 and SL-34 isn’t fading anytime soon, and their prominence in the world of specialty coffee is here to stay.