When you buy a bag of single origin, roasted Kenyan coffee, it’s common to see the coffee varietals SL-28 and SL-34 listed on the bag - but what does this mean exactly?

What does SL stand for?

SL stands for Scott’s Laboratories, which is a research program that has operated in Kenya since the 1920s. They mainly conduct coffee varietal research relating to cup quality, resistance to pests and diseases, and yield potential. Lee Knuttila, the owner of Quietly Coffee, says his “long-standing love of Kenyan coffees is inexorably tied to Scott Labs.” Over time, the lab identified and separated SL-28 and SL-34 as Bourbon-related varietals, and have since been two popular varieties grown by Kenyan producers.

Why plant SL-28 or SL-34?

From a coffee agronomy angle, coffees that yield higher cup quality are generally more susceptible to disease and pests. The opposite is also common: when a varietal is high yielding, and pest and disease resistant, they usually cup with more tasting notes relating to bitterness, astringency, with an overall lower cup quality. Some of the greatest benefits of SL-28 and SL-34 are that they strike a balance between disease and pest resistance, yield potential, and cup quality.

Because it is estimated that up to 80% of all exported Kenyan coffees contain SL series coffees, producers benefit from receiving higher cherry prices due to the demand for these varietals. You might be able to identify an SL-28 and SL-34 plant from them being tall trees, bearing large cherries, and their brown/bronze shoot tips.

The taste of Kenyan coffees

Kenyan coffees are usually prized for their high cup quality, and when grown at optimal conditions, they can yield highly sought-after flavours and characteristics. For example, many roasters and green buyers seek floral and black tea notes, blackcurrant and blackberry-like flavours, bright acidity, and sometimes even a savoury, umami, tomato note. Knuttila believes great Kenyan coffees can simultaneously embody all three qualities of the specialty coffee trinity- sweet, juicy and clean. "With sparkling acidity, incredible depth of sweetness, eating-fruit-over-the-sink mouthfeel, they can easily provide all those qualities that I associate with a great cup.”

Phosphoric Acid in specialty coffee?

For the more nerdy coffee enthusiasts out there, one differentiating aspect of Kenyan coffees, and SL-28 and SL-34 in particular, may be the presence of a higher amount of phosphoric acid in the coffee. Typical acids you can taste/feel in coffees include citric, malic, and acetic as organic acids, as well as phosphoric acid as an inorganic acid. What’s interesting about phosphoric acid is that it is not so much an acidic flavour, rather it is more a texture of bubbly/effervescence on the palate. If you’ve ever seen the tasting note “sparkling acidity” or “champagne,” these usually describe the presence of phosphoric acid. For some palates, this may not exactly be a soda/pop-like experience, and may instead feel like the coffee is jumping/lifting slightly off their palate. This sensation enhances the overall flavour of the coffee. “It is that meeting point between texture and flavour that really pushes perceived flavour notes like grape or blackberry further making them vibrant, present, pleasant, and lively,” Knuttila says. Definitely a fun sensation, so look out for this feeling when you brew coffees - Kenyan or not! 

Although many Kenyan coffees are known to have a “distinct Kenyan flavour” that is reflected from the tasting notes above, we are slowly learning more about Kenyan coffee varietals and regions. In last month’s issue, we featured a Kenyan coffee from Ndaro-Ini factory, sourced through Vava Angwenyi. She runs Vava Coffee in Kenya, and in the past years has been outspoken about the intricacies and complexities surrounding regional coffee flavour profiles. As we continue to learn more about coffee through our role models, we are finding increasingly more variability and diversity in the flavour profiles of Kenyan coffees. When it comes to SL-28 and SL-34, Knuttila associates strong floral notes with the varieties, “think viburnums, stocks, hibiscus, and chrysanthemums."



July 28, 2022 — Zara Snitman

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