What Is SL28 Coffee?

by Marcus McCombe | Aug 12, 2026

What Is SL28 Coffee?

TL;DR

SL28 is a coffee variety developed by Scott Laboratories in Kenya in 1931. The SL stands for Scott Laboratories, and 28 refers to the selection number. SL28 produces some of the most vivid and intense flavours in all of coffee: blackcurrant, grapefruit, blood orange, cranberry, and a sparkling, wine-like acidity. Moreover, SL28 defines Kenyan coffee. Alongside its sibling SL34, it accounts for the vast majority of Kenya’s specialty production and gives Kenyan coffee its reputation as some of the most distinctive and complex in the world. Furthermore, SL28 now grows beyond Kenya, with producers in Nicaragua, Colombia, and elsewhere planting it for its extraordinary cup quality.

The Quick Answer

If you have ever tasted a Kenyan coffee and thought it tasted like no other coffee you have tried, SL28 is a big part of the reason. The variety produces flavour intensity that other varieties simply cannot match. The blackcurrant. The grapefruit. The blood orange. The acidity that sparkles rather than stings. These are SL28 signatures, and they are what make Kenyan coffee one of the most celebrated and instantly recognisable origins in specialty coffee.

This article explains where SL28 comes from, what makes it taste the way it does, how it differs from SL34, and where it grows today. For the variety SL28 descends from, read our guide on what Bourbon coffee is.

The Origin Story

In the 1930s, Scott Agricultural Laboratories (later known as the National Agricultural Laboratories) in Nairobi began a systematic programme to identify and select coffee varieties suited to Kenya’s growing conditions. Researchers evaluated dozens of coffee accessions for drought tolerance, yield, disease resistance, and cup quality. Selection number 28 stood out.

Scott Laboratories selected SL28 from material originally classified as “Tanganyika Drought Resistant,” which had roots in the Bourbon genetic group. Moreover, the variety demonstrated exceptional drought tolerance alongside a cup quality that surpassed most other selections. Researchers recognised immediately that SL28 produced flavours unlike anything else available at the time: intense citrus, dark berry, and a phosphoric acidity that gave the cup a sparkling, almost effervescent quality.

At the same time, Scott Laboratories also developed SL34 from a separate selection. Together, SL28 and SL34 became the backbone of Kenyan coffee production. By the mid-twentieth century, the two varieties dominated Kenya’s coffee farms, particularly in the high-altitude regions around Mount Kenya. They remain dominant today, forming nearly 90 percent of the coffee grown in many Kenyan regions.

What Does SL28 Coffee Taste Like?

SL28 produces flavours that many coffee professionals consider the most intense and distinctive of any variety. Common tasting notes include:

Blackcurrant. The signature SL28 note. Deep, dark, and unmistakable. Moreover, blackcurrant in SL28 is not a subtle background note. It sits at the centre of the cup and defines the experience. No other coffee variety produces blackcurrant with this intensity.
Grapefruit and blood orange. Vivid, high-toned citrus that provides structure and brightness. Furthermore, the citrus in SL28 tends to be juicy and complex rather than sharp or one-dimensional. For more on fruity flavours, read our guide on why coffee tastes fruity.
Cranberry and red currant. Tart, bright, and acidic berry notes that add complexity alongside the blackcurrant.
Tomato-like acidity. A distinctive savoury quality that appears in the best Kenyan coffees. Moreover, this note sounds unusual but in context it adds depth and a mouth-watering quality to the cup.
Sparkling, phosphoric acidity. This is what sets Kenyan SL28 apart from almost every other coffee. The acidity does not taste sharp or biting. It sparkles, almost like carbonation. Furthermore, Kenya’s volcanic soils, rich in phosphoric compounds, contribute directly to this quality. For more on how acidity works in coffee, read our guide on what coffee acidity is.
Wine-like body. SL28 produces a medium body with a wine-like texture: structured, complex, and lingering. Moreover, this quality makes SL28 one of the few coffee varieties that genuinely invites comparison with wine.
Brown sugar sweetness. Underlying all the fruit and acidity is a clean sweetness inherited from SL28’s Bourbon ancestry. This sweetness balances the intensity and prevents the cup from tasting aggressive. For more on sweetness, read our guide on what makes coffee sweet.

The intensity of these flavours is what defines SL28. Other varieties can produce citrus, berry, or bright acidity. But no other variety produces them at the volume and clarity that SL28 achieves when grown well at altitude in the right soils.

Why Kenyan SL28 Tastes the Way It Does

SL28’s extraordinary flavour profile is not just about genetics. Several factors unique to Kenya amplify what the variety can do:

Volcanic soils. Kenya’s coffee regions sit on volcanic soils rich in phosphoric acid and trace minerals. Moreover, these soil compounds contribute directly to the sparkling, phosphoric acidity that defines Kenyan coffee. The same variety grown in different soils produces good coffee but rarely achieves the same effervescent quality.
High altitude. Kenyan SL28 grows at 1,500 to 2,100 metres, often on the slopes of Mount Kenya, the Aberdare Range, and surrounding highlands. Furthermore, cooler temperatures at altitude slow cherry maturation, allowing more sugars and complex acids to develop inside the bean.
Double-soaking washed process. Kenyan processing typically uses a double-soaking method that intensifies clarity and brightness. After pulping and fermenting, processors soak the beans in clean water for an extended period, then soak them again. This additional soaking step washes away residual mucilage and produces an exceptionally clean cup that lets the variety’s natural intensity shine.
Biannual harvests. Kenya has two harvest seasons per year (main crop and fly crop). Moreover, the main crop harvest, typically from October to December, produces the highest-quality lots.

Together, these factors create a growing and processing environment that maximises SL28’s genetic potential. The variety provides the raw material. Kenya’s terroir and processing traditions amplify it into something extraordinary.

SL28 Versus SL34

SL28 and SL34 are siblings from the same Scott Laboratories programme, and they often grow together on the same farms. However, they differ in subtle but meaningful ways:

SL28 tends to produce more intense citrus and blackcurrant notes with higher, more sparkling acidity. Furthermore, SL28 generally scores slightly higher in cupping competitions for its complexity and brightness.
SL34 tends to produce a heavier body with more sweetness, stone fruit, and chocolate notes. Moreover, SL34 is sometimes described as the “rounder” of the two, with softer acidity and more body.

In practice, most Kenyan coffee lots contain a blend of SL28 and SL34, because both grow on the same farms and producers process them together. Furthermore, the differences between the two are often smaller than the differences between growing regions, altitudes, or processing approaches. Both produce exceptional coffee, and both contribute to what the world recognises as “the Kenyan taste.”

SL28 Beyond Kenya

SL28 is no longer exclusive to Kenya. Producers in several other countries now grow the variety, drawn by its exceptional cup quality:

Nicaragua. Our Nicaragua Finca Libre grows SL28 and SL34 at 1,600 metres in the Mozonte mountains. Moreover, Finca Libre processes this Kenyan variety using natural carbonic maceration, a technique borrowed from winemaking. The result is clementine, red fruits, and pineapple: a completely different expression of SL28 from the typical Kenyan profile. The natural carbonic maceration amplifies fruit sweetness and body, demonstrating how SL28 responds to processing methods beyond Kenya’s traditional double-soaking wash. Read our guide on carbonic maceration.
Colombia. Some Colombian producers have planted SL28 at altitude, attracted by its flavour complexity. Furthermore, Colombian SL28 processed anaerobically or with fruit fermentation produces results that blend Kenyan intensity with Colombian processing innovation.
Guatemala and other Central American origins. Small plantings exist across the region, though volumes remain low. Moreover, the variety’s susceptibility to coffee leaf rust limits its viability in regions where rust pressure is high.

When SL28 grows outside Kenya, the flavour profile shifts. The blackcurrant and phosphoric acidity are less pronounced without Kenya’s volcanic soils, but the variety’s underlying intensity and complexity still come through. Furthermore, processing methods unavailable in Kenya’s washed tradition (natural, anaerobic, carbonic maceration) unlock new dimensions of SL28’s flavour potential.

SL28 in the Coffee Family Tree

Genetic analysis places SL28 firmly in the Bourbon family. Scott Laboratories selected it from “Tanganyika Drought Resistant” material that descended from Bourbon stock. As a result, SL28 is essentially a Bourbon selection that developed in East African conditions.

This Bourbon connection explains the sweetness that underlies SL28’s intense fruit and acidity. Moreover, it places SL28 alongside Caturra, Pacas, and other Bourbon descendants in the coffee family tree, though SL28’s flavour profile is dramatically different from its Latin American cousins.

Parent variety: Bourbon (via Tanganyika Drought Resistant). Read our guide on what Bourbon coffee is.
Sibling: SL34 (from the same Scott Laboratories programme).
Cousins: Caturra (Bourbon mutation, Brazil), Pacas (Bourbon mutation, El Salvador).
Newer Kenyan varieties: Ruiru 11 and Batian were developed more recently for disease resistance, gradually replacing some SL28 and SL34 plantings. However, neither matches the cup quality of the original SL selections.

SL28 Coffee at Routes

We currently offer SL28 in two very different expressions:

Kenya Acacias from Nyeri showcases SL28 in its natural habitat. Washed, light roasted, with tasting notes of blackberry, apple, and citrus fruits. This is classic Kenyan SL28: bright, complex, and unmistakable. The lot includes Bourbon and Kent alongside SL28, grown across the Central Highland Range near Mount Kenya at high altitude in rich volcanic soil.
Nicaragua Finca Libre takes SL28 and SL34 to Central America and processes them through natural carbonic maceration. Clementine, red fruits, and pineapple. This is what happens when a Kenyan variety meets Latin American processing innovation: the intensity of SL28 expressed through a completely different lens.

Tasting these two side by side is one of the best ways to understand how origin, terroir, and processing shape the same variety into different experiences.

Alternatively, a Routes Coffee subscription delivers a rotating selection of specialty coffees to your door, starting from £9 with free UK delivery. Kenyan and SL28 lots appear in the lineup when they are in season.

Frequently Asked Questions

What is SL28 coffee?

SL28 is a coffee variety developed by Scott Laboratories in Kenya in 1931. The SL stands for Scott Laboratories, and 28 refers to the selection number. Researchers selected it from Bourbon-related genetic material for its drought tolerance and exceptional cup quality. SL28 produces some of the most vivid and intense flavours in all of coffee, including blackcurrant, grapefruit, blood orange, and a complex, wine-like acidity.

What does SL28 coffee taste like?

SL28 produces intensely fruity, bright, and complex cups. Common tasting notes include blackcurrant, grapefruit, blood orange, cranberry, tomato-like acidity, and a wine-like body. Furthermore, the acidity in SL28 is sparkling and phosphoric rather than sharp, which gives Kenyan coffees their distinctive brightness. No other variety produces quite the same intensity of citrus and dark berry flavours.

Where does SL28 coffee grow?

SL28 is most closely associated with Kenya, where it has been a dominant variety since the mid-twentieth century. Major Kenyan growing regions for SL28 include Nyeri, Kirinyaga, Kiambu, Murang’a, and Embu. However, SL28 now grows in several other countries, including Nicaragua, Colombia, and Guatemala, where producers have planted it for its exceptional cup quality.

What is the difference between SL28 and SL34?

Both SL28 and SL34 were developed by Scott Laboratories in Kenya and produce excellent cup quality. SL28 tends to produce more intense citrus and blackcurrant notes with higher acidity. SL34 tends to produce a heavier body with more sweetness and stone fruit character. In practice, most Kenyan coffee farms grow both varieties together, and many lots blend them. Both trace their genetics back to the Bourbon family.

Is SL28 related to Bourbon?

Yes. Genetic analysis confirms that SL28 belongs to the Bourbon genetic group. Scott Laboratories selected it from Tanganyika Drought Resistant material, which descended from Bourbon stock. As a result, SL28 shares some of Bourbon’s underlying sweetness but expresses it with far more intensity, acidity, and fruit complexity than typical Bourbon.

Why is Kenyan coffee so distinctive?

Several factors combine to make Kenyan coffee unique. SL28 and SL34 varieties provide exceptional genetic flavour potential. Kenya’s volcanic soils are rich in phosphoric acid, which contributes to the sparkling acidity. High altitudes (1,500 to 2,100 metres) develop complexity. Furthermore, Kenya’s double-soaking washed process intensifies clarity and brightness. Together, these factors produce coffees with an intensity of flavour rarely matched by any other origin.