SL9: The mysterious coffee variety behind Peru's Inca Gesha

SL9 is an unusual name to find on a bag of Peruvian coffee.

The “SL” prefix usually points to Kenya's Scott Agricultural Laboratories, the research station behind varieties such as SL28 and SL34. SL9 was one of the earlier selections in that programme, and historical records suggest it was never widely distributed.

Then genetic testing linked coffee trees in Peru, commonly known as Inca Gesha, to the same genetic reference. That raised a fairly obvious question: how did a coffee associated with a long-forgotten Kenyan selection end up in Peru?

At the moment, nobody can answer that with certainty.

What does “SL” mean?

The SL varieties were selected by the Scott Agricultural Laboratories in Kenya during the 1930s. Researchers examined individual coffee trees from different populations, looking for plants with useful combinations of productivity, quality and other agronomic characteristics.

Each selected tree was given an SL number. Some became commercially important. SL28 and SL34 are the obvious examples, while many of the other selections disappeared from widespread cultivation.

SL9 appears to have been one of the less successful selections. A Coffee Board of Kenya bulletin from 1956 describes it as a single-tree selection from a block of uncertain origin, with low productivity and high susceptibility to Coffee Berry Disease. It was not developed into an important commercial variety.

That history is what makes the modern Peruvian material so interesting.

From Kenya to Peru?

The first thing to establish is what the DNA testing actually showed.

Several researchers and coffee companies have had samples of Peruvian trees tested independently. The trees were originally being grown under names including Inca Gesha, Gesha Inca and Gesha Inka.

The results showed that these trees were not genetically equivalent to the Gesha variety. Instead, they clustered with a group of Ethiopian-related coffee material and came very close to the reference sample used for SL9.

That is where the careful wording matters. The tests suggest that the Peruvian trees may be the same genetic material as SL9. They don't prove that a Kenyan SL9 plant was physically transported from Kenya to Peru.

There is no documented seed trail connecting the original Scott Laboratories selection with the trees now growing in the Peruvian Andes.

So what is growing in Peru?

The name Inca Gesha predates the genetic testing. Farmers and buyers used it because the coffee looked and tasted similar to Gesha, and the name had become established locally.

Once the DNA results became known, some exporters and roasters began using SL9 instead. That makes sense from a genetic-identification perspective, but it also creates a strange situation: the trees are being given the name of a Kenyan selection even though there is no evidence that the Peruvian plants travelled through Kenya.

Christopher Feran's investigation into the history makes this distinction particularly important. He argues that even if the Peruvian trees turn out to have the same genetic background as SL9, it may make more sense to regard Inca Gesha as a locally established coffee population in its own right.

The name reflects where the coffee is grown and how the farmers themselves came to know it. The genetic label answers a different question.

How could it have arrived in Peru?

There isn't a single accepted explanation. Several possibilities have been proposed.

The Tingo María route

In 1964 and 1965, scientists working through the United Nations Food and Agriculture Organization collected coffee seed from Ethiopia. Hundreds of resulting plants were sent to Peru's Tingo María Experimental Station.

The station later suffered several attacks during the years of conflict involving Sendero Luminoso. Buildings, records and research material were destroyed, leaving major gaps in the history of the plants that had been grown there.

It's possible that Ethiopian-derived material from this programme eventually found its way into farmers' fields, where it was propagated for generations without retaining its original name.

The Columnaris possibility

Another theory involves Columnaris, a coffee variety that appeared in the Scott Laboratories records and shares some characteristics with the material now called SL9.

Columnaris has a complicated history of its own. It originated in Java, was grown in Puerto Rico and Kenya, and later appeared in Peru. Feran's research raises the possibility that some of the coffee now called SL9 could actually trace back to this material, rather than the specific Scott Labs SL9 tree.

Older introductions

There are also earlier routes worth considering. Coffee had already reached Peru well before the twentieth-century research programmes, and different varieties moved between colonial territories, plantations and research stations over many years.

Dr Christophe Montagnon has suggested that the ancestors of the Peruvian trees may have arrived through an older introduction and then remained unrecognised until much later.

A more recent Central American route

More recent research has added another possibility. Feran's 2026 update discusses evidence suggesting that some Peruvian farmers believe the original trees were brought from Central America during the 1990s.

That theory isn't established either. It's simply another possible route in a story where the documentary trail is incomplete.

A new clue from Kenya

There is one particularly curious piece of evidence.

London roaster Scenery Coffee recently described growing a coffee tree from Kenyan Mbuni cherries they had brought home as a training sample. Out of around 50 seeds, only two survived the earliest stage, and one tree was eventually kept alive in the café for several years.

When a leaf sample from the tree was tested, it came back as SL9.

It's an intriguing result, but it shouldn't be overinterpreted. One tree and one genetic result don't establish the distribution history of SL9. What they do show is that material matching the SL9 reference appears to exist in Kenya today, despite the variety's old reputation for being effectively lost.

What does SL9 taste like?

This is where the story gets much simpler.

The Peruvian coffees sold as SL9 or Inca Gesha can be intensely aromatic, with a style that helps explain why the Gesha name caught on in the first place.

Floral notes are common, with jasmine, honeysuckle and bergamot appearing in descriptions of different lots. Fruit can range from citrus and stone fruit to tropical flavours such as passionfruit and lychee.

The mouthfeel is often light and tea-like, with pronounced acidity and plenty of sweetness.

Those characteristics aren't a guaranteed varietal fingerprint. The coffees involved come from different farms, elevations and processing methods, and the genetic identity itself is still being investigated.

Still, the resemblance to high-quality washed Ethiopian coffees and some Gesha lots is hard to miss.

Where is it grown in Peru?

The best-known Inca Gesha and SL9 coffees come from high-altitude farms in Peru.

One important cluster is around the Inkawasi Valley in La Convención, Cusco. Farms in this area can sit at more than 2,000 metres above sea level, and producers including Finca Tres Cedros and Finca Nueva Esperanza have brought Inca Gesha coffees to international buyers.

There is also growing interest in the variety in Jaén, Cajamarca, in northern Peru. Our first SL9 comes from Finca La Palestina in the San José del Alto district, where the Alarcón Coronel family has been working with Origin Coffee Lab on renovation and the introduction of newer varieties.

Our first SL9: Peru La Palestina Washed

Finca La Palestina belongs to the Alarcón Coronel family and has been farmed across several generations. The coffee is processed at a central wet mill operated by the family, where fermentation and drying are managed alongside coffees from their other parcels.

The farm has also placed in the Peru Cup of Excellence, and in recent years the family has been introducing new planting material alongside older Bourbon, Caturra and Pache trees.

We bought this coffee in the way we'd hope to buy any variety: by tasting it first.

The floral character and fruit stood out on the cupping table. The questions about what the coffee actually was came afterwards.

That seems appropriate for SL9. The name is still being figured out. The coffee doesn't need to wait.

SL9 or Inca Gesha?

For now, we'd treat both names with a little caution.

SL9 is useful because it tells us something about the genetic testing and gives buyers a way to connect the Peruvian material with a historical reference sample.

Inca Gesha is useful because it describes the coffee as it has actually been grown and known in Peru.

Neither name completely explains the origin of the trees.

That's likely to remain the case until researchers can match the living Peruvian plants with better-documented reference material and, ideally, find some historical record of how that material travelled.

Why this coffee is worth paying attention to

SL9 is interesting for two quite separate reasons.

First, the coffees themselves can be excellent. The combination of floral character, tropical fruit, high sweetness and tea-like structure is enough to make them worth seeking out.

Second, the variety is a useful reminder of how incomplete coffee's genetic record still is. Plants moved between countries for decades, sometimes without proper documentation, and names were often applied retrospectively. In some cases, the original records were simply destroyed.

SL9 sits somewhere in that gap between what we can prove and what we can reasonably suspect.

That's a good place for a coffee mystery to live.

Quick varietal facts

Varietal: SL9, often marketed in Peru as Inca Gesha or Gesha Inca
Species: Coffea arabica
Historical origin: Scott Agricultural Laboratories, Kenya, 1930s
Peruvian identity: Genetically very close to the SL9 reference material, but the historical connection has not been proven
Genetic background: Ethiopian-related material; exact identity and relationship to the original SL9 selection remain under investigation
Growth habit: Tall, with broad leaves and copper-coloured young growth reported in Peruvian populations
Cherry colour: Red
Yield: Low; historical Kenyan records describe SL9 as a shy bearer
Disease resistance: Poor; historical sources report high susceptibility to Coffee Berry Disease and the material is also susceptible to coffee leaf rust
Key growing regions: Peru, particularly Cusco and Cajamarca
Common processing: Washed, with natural and other experimental processes also used
Typical cup profile: Floral and tea-like, with jasmine, honeysuckle, bergamot, citrus and tropical fruit; pronounced acidity and high sweetness

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