SL34
SL34 is the coffee plant that almost always shows up next to SL28 on a bag of Kenyan coffee. The two were picked out of Kenyan research fields in the same decade, by the same institution, and they get shipped, sold and described together — but they are not relatives, and the story of how that was discovered is the most interesting thing about SL34.
The name is a filing code. SL stands for Scott Agricultural Laboratories, the Kenyan research station that did the selecting; 34 is the serial number that particular tree was given.
For most of its life SL34 was described as a Bourbon — because the tree it came from carried a label saying so. Genetic testing eventually said otherwise.
Where it came from
Everything in this section is from the World Coffee Research variety record for SL34 (accessed 2026-07-23, confirmed via WebFetch) unless noted. WCR’s catalogue, maintained by World Coffee Research, is the specialty industry’s reference database for coffee varieties.
- SL34 was selected in Kenya in the late 1930s, at Scott Agricultural Laboratories.
- It came from one single tree growing on Loresho Estate in Kabete, Kenya — a private farm, not a research plot.
- That tree was labelled “French Mission.” The label refers to French missionaries who planted Bourbon seed from the island of Réunion at a mission in Kenya’s Taita Hills in 1893; “French Mission” became the Kenyan trade name for that Bourbon material.
- Despite the label, SL34 is not a Bourbon. WCR states that “recent genetic tests have indicated that SL34 is related to the Typica genetic group,” and places it in the Bourbon-Typica group (Typica related).
So the paperwork and the DNA disagree, and the DNA wins. This is why this wiki files SL34 under Typica rather than Bourbon — see both notes, which record the same finding. Its stablemate SL28 does still test as Bourbon-related, which means the two most famous Kenyan varieties sit on opposite branches of the Arabica family tree despite being sold as a pair.
Ulu Coffee Farm in Kona, Hawaii — a grower who planted SL34 — describes the same history in the same terms: a variety “created by the former Scott Agricultural Laboratories in Kenya,” descended from a single tree labelled “French Mission,” with genetic testing indicating Typica (confirmed via WebFetch).
To verify
No primary Scott Laboratories document was located. The selection date (“late 1930s,” within the 1935–1939 SL programme), the Loresho Estate location and the original “French Mission” label all come from later technical summaries and farm histories rather than a digitised original report. WCR is the most authoritative of those, and independent sources agree with it, but nobody consulted here has seen the underlying record. Note also that the sibling SL28 note already flags an unresolved dispute over Scott Labs’ founding date and its successor institution — the same uncertainty applies to SL34’s paperwork.
What the plant is like
From the World Coffee Research record (accessed 2026-07-23, confirmed via WebFetch):
| Trait | SL34 |
|---|---|
| Stature | Tall |
| Leaf tip colour | Dark bronze — though WCR also records “a few green-tipped strains” |
| Bean size | Large |
| Yield potential | Medium to low |
| Quality potential at high altitude | Exceptional |
| Nutrition requirement | Medium |
| First harvest | Year 3 |
| Cherry-to-green-bean outturn | High |
| Coffee leaf rust | Low resistance / susceptible |
| Coffee berry disease | Susceptible |
| Nematodes (root-attacking soil worms) | Susceptible |
WCR’s own one-line summary is blunt: “exceptional cup quality but highly susceptible to coffee berry disease.” That is the whole trade-off in a sentence. Like SL28, SL34 catches everything — rust, berry disease, root nematodes — and farms keep it anyway because of what it does in the cup.
Two numbers are worth pulling out. Cherry-to-green-bean outturn is High, meaning a sack of picked cherry converts to more sellable green coffee than average, which partly offsets the modest yield. And first production comes in year three, so a new planting is three years from paying anything back.
Optimal altitude is stated as a sliding scale, because how high a farm needs to be depends on how far it is from the equator: above 1,200 m between 5°N and 5°S, above 900 m at 5–15°, above 700 m beyond 15°. WCR describes the variety as adapted to high-altitude areas with good rainfall. Ozone Coffee narrows that to a practical 1,500–2,100 m working range (confirmed via WebFetch).
WCR records SL34 as primarily found in Kenya — it has travelled far less than SL28, which spread into Uganda, Malawi, Zimbabwe and Latin America.
One more shape detail from the same record: the side branches sit at a semi-erect angle and tend to droop on the older primary branches — WCR’s exact wording is “the laterals have semi-erect habit which tend to droop on older primary branches” (confirmed via WebFetch, 2026-07-23). In plain terms, a young SL34 holds its fruiting branches up at roughly 45 degrees, and as the tree ages the lower, older branches sag under their own weight and their crop. That is normal for the variety, not a sign of a sick tree.
To verify
Sources contradict each other on whether SL34 out-yields SL28. Perfect Daily Grind says SL34 has “slightly lower yields” than SL28 and is “more demanding in terms of nutrition” (confirmed via WebFetch) — and this wiki’s existing SL28 note repeats that in its comparison table. World Coffee Research’s catalogue says the opposite on yield: SL34 rates “Medium to Low” while SL28 rates “Low” (both confirmed via WebFetch, 2026-07-23). The nutrition claim does hold up — WCR puts SL34 at Medium and SL28 at Low. Treat the yield comparison as unsettled; the SL28 note’s table should not be read as verified on that point.
Ozone Coffee gives a figure of 4–6 kg of cherry per tree per year (confirmed via WebFetch). That is a single roaster-facing source with no trial behind it, and MTPak Coffee separately calls both SL varieties “high yields” — flatly at odds with WCR. Don’t quote a per-tree number as fact.
How to tell it apart from SL28
The two trees look nearly identical in the field. The give-away is the colour of the new leaf tips: dark bronze on SL34, green on SL28. Perfect Daily Grind calls it “the only major visual difference” between them (confirmed via WebFetch), and WCR’s own trait tables record exactly that split.
Two caveats, both added 2026-07-23, and together they take most of the weight out of that field test.
The first: the SL28 note flags that two secondary sources describe SL28 as bronze-tipped too, contradicting WCR. So a bronze leaf tip on a Kenyan tree is not by itself proof that the tree is SL34.
The second comes from WCR itself, and it cuts the other way. The same record that gives SL34 its dark bronze tips adds that there are “a few green-tipped strains” of SL34 (confirmed via WebFetch, 2026-07-23). So a green tip is not proof the tree is SL28 either. The honest summary: most SL34 is bronze-tipped and most SL28 is green-tipped, but the colour is a strong hint rather than an identification. Anything that actually matters — a variety declaration on a contract, say — needs genetic testing, not a look at the new growth.
| SL34 | SL28 | |
|---|---|---|
| Leaf tip colour | Dark bronze (some green-tipped strains) | Green |
| Genetic group (WCR testing) | Typica-related | Bourbon-related |
| Origin population | A “French Mission” (Bourbon) tree, Loresho Estate | Tanganyika Drought Resistant population |
| Nutrition requirement | Medium | Low |
| Drought | Not rated as tolerant | Tolerant |
| Spread beyond Kenya | Limited | Wide |
The drought line matters most in practice. SL28’s rusticity — its ability to be abandoned for years and come back into production — comes from the drought-hardy Tanzanian material it was selected from. SL34 has no equivalent inheritance, and WCR ties it instead to good rainfall. In the same field, the two plants want different weather.
What it tastes like
World Coffee Research’s formal rating at high altitude is one word: “Exceptional.” That is the top band in its catalogue, shared with SL28 and very few others.
Beyond the rating, descriptions come from roasters rather than any controlled sensory study, and they converge on a heavy, dark-fruited, wine-like cup. Ozone Coffee lists bold winey acidity, blackcurrant, dark cherry, syrupy body, dark chocolate and a black-tea finish (confirmed via WebFetch). MTPak Coffee ties SL34 to Kenya’s broader reputation for “a rich body, bright acidity, and distinctive berry undertones” (confirmed via WebFetch). Ulu Coffee’s own note on their trees is shorter: “complex acidity, full mouthfeel, fruity flavors.”
Read those as the trade’s shared impression, not a measurement. See Cupping and Coffee scoring for how cup quality is actually assessed.
Kenyan SL34 is conventionally washed, and typically double-washed — fermented, rinsed, then soaked again in clean water before drying. See Washed process.
To verify
No numeric cupping scores, auction prices, buyers or competition placements could be verified for SL34. The practical reason is structural: SL34 is almost always harvested and sold blended with SL28 under grade names like “Kenya AA,” and auction catalogues rarely break lots down by variety. No Cup of Excellence, Alliance for Coffee Excellence or Specialty Coffee Association record isolating SL34 as the variety was located. Any specific SL34 price or score figure is a synthesis, not a citation.
Grown outside Kenya
SL34 has not travelled the way SL28 did, but two documented plantings are worth recording:
- Café Granja La Esperanza, Colombia. A single-variety SL34 lot from Finca Potosí in Caicedonia, Valle del Cauca, grown by Rigoberto and Luis Eduardo Herrera at 1,400–1,860 m. Processing is a “hybrid washed” method — a 14-hour open-tank fermentation, then an 18-hour oxygen-free fermentation, then depulping and further aerobic fermentation. Tasting notes given by the seller: pink strawberry, tree tomato, pink florals (Hydrangea Coffee, confirmed via WebFetch). The oxygen-free stage makes this a form of Anaerobic fermentation.
- Ulu Coffee Farm, Kona, Hawaii. Planted 200 SL34 saplings in 2021, alongside existing two-year-old SL34 trees in a second orchard, and alongside Kona Typica and Geisha (Ulu Coffee Farm, confirmed via WebFetch). No altitude or scores published.
Both are grower/seller descriptions rather than independent records. Note that the research report behind this note gave the Colombian lot’s elevation as 1,570–1,850 m and placed the farm in Cauca; the seller’s own page says 1,400–1,860 m in Valle del Cauca, and the seller’s figure is used here.
To verify
Several sources describe SL34 spreading out of Kenya through informal seed swaps and “back alley deals,” producing mislabelled planting material around the world. That is plausible and widely repeated, but it is anecdote — no trade record, phytosanitary document or breeder’s register was found to support it. Related: no plant breeders’ rights, patent or formal ownership status for SL34 was located in any source, so nothing can be said about who, if anyone, controls the variety today. On the evidence available, SL34 is a publicly known Kenyan selection rather than a privately controlled commercial cultivar — but that is an absence of evidence, not a document saying so.
To verify
How official SL34 planting material is produced in Kenya is claimed by one weak source only. Bean Brew Digest states that “all certified SL34 seed stock in Kenya is propagated via grafting or tissue culture from mother trees maintained at the Kenya Agricultural and Livestock Research Organization (KALRO) station in Ruiru” (confirmed via WebFetch, 2026-07-23). That is a specific, checkable claim about a real institution — KALRO’s Ruiru station is the successor to the Coffee Research Foundation that bred Ruiru 11 and Batian — but it appears in a single SEO-style article with no KALRO document behind it, and no KALRO or Kenyan government page confirming it was located. Note the internal oddity too: “seed stock” propagated by grafting or tissue culture is a contradiction in terms, since neither method produces seed. Do not repeat the propagation route as fact.
The same page also describes SL34 as “a selection of Coffea arabica var. typica” sharing ancestry with “the original Yemeni typica landraces brought to East Africa via Ethiopia and Sudan.” The Typica placement matches WCR, but the specific Yemen-via-Ethiopia-and-Sudan migration route for this variety is that source’s own framing and is not in the WCR record.
Related
- SL28 — the stablemate it is always sold beside, and the one that really is a Bourbon
- Typica — the genetic group testing actually places SL34 in
- Bourbon — the family its “French Mission” label claimed, incorrectly
- Scott Agricultural Laboratories — the Kenyan research station that selected it
- World Coffee Research — keeper of the variety catalogue this note leans on
- Coffee leaf rust · Coffee berry disease — the two diseases it has no defence against
- Ruiru 11 · Batian — the disease-resistant Kenyan varieties bred to replace the SL pair; Batian carries SL34 in its pedigree
- KALRO — the Kenyan state research body that now holds the country’s coffee breeding programme, and the claimed source of certified SL34 planting material
- Nairobi Coffee Exchange — the auction system Kenyan SL lots are sold through
- Washed process · Anaerobic fermentation — the processing styles it appears under
- Cupping · Coffee scoring — how its “exceptional” rating would be measured
- Geisha — the other variety whose reputation rests almost entirely on the cup
Official links
Sources
- World Coffee Research — SL34 — accessed 2026-07-23
- World Coffee Research — SL28 — accessed 2026-07-23
- Perfect Daily Grind — Exploring popular Kenyan coffee varieties: SL-28 & SL-34 — accessed 2026-07-23
- MTPak Coffee — SL28 and SL34: a coffee roaster’s guide — accessed 2026-07-23
- Ozone Coffee — SL34 coffee varietal: Kenya’s Typica mystery — accessed 2026-07-23
- Ulu Coffee Farm — Kona Typica, SL-34 and Gesha — accessed 2026-07-23
- Hydrangea Coffee — SL34 hybrid washed, Café Granja La Esperanza — accessed 2026-07-23
- Green Coffee Collective — SL-34: Kenya’s fruit-forward Scott Labs variety — accessed 2026-07-23
- Roastopedia — SL34 coffee: history, characteristics, cultivation, flavor — accessed 2026-07-23
- Bean Brew Digest — SL34 variety genetics and flavor — accessed 2026-07-23