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 SL34.¹²

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 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.

The old label has not gone away. Morning Wines, an educational coffee wiki, still describes SL34 as sharing “Bourbon ancestry” and gives no Typica classification for it at all, while correctly reporting the Bourbon result for SL28.³ That is worth knowing not because it settles anything — WCR’s genetic testing is the more authoritative source and this note follows it — but because it shows how durable the “French Mission” paperwork is. A reader will keep meeting SL34 described as a Bourbon on bags, menus and reference pages.

The third Scott Laboratories selection in WCR’s catalogue, SL14, lands on the same side of the family as SL34: WCR places it in the Bourbon-Typica group (Typica related), selected in 1936 from a single tree labelled “Drought Resistant II,” and rates its cup only “Good” against SL34’s “Exceptional.”⁴

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.⁵

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.

One source pins the year to 1935. Roastopedia writes that “in 1935, a single outstanding tree was selected from the Loresho Estate in Kabete” — confirmed by reading the page.² That is a plausible year, since it sits at the start of the 1935–1939 window WCR gives for the Scott Labs selection programme, but WCR itself says only “late 1930s” for SL34, and no other source consulted names a year for this particular tree. Treat 1935 as one source’s precision, not a documented date.

And one source names a completely different farm. Bean Brew Digest says SL34 “was selected from a single tree growing on the Loima Hills estate in Nyanza Province, near Lake Victoria” — confirmed by reading the page, which never mentions Loresho or Kabete at all.⁶ That is not a small discrepancy: Nyanza sits on Kenya’s western edge by Lake Victoria, while Kabete is on the outskirts of Nairobi, most of the country away. Every other source consulted — WCR, Ozone, Roastopedia, Green Coffee Collective, Ulu Coffee — says Loresho, Kabete. This note follows them and treats the Loima Hills claim as an error in a single weak source, but it is recorded here so a reader who meets it elsewhere knows where it came from.

What the plant is like

From the World Coffee Research record:⁷

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.⁸

Four secondary sources give a working band, and they broadly agree on where SL34 belongs:

	Source	Stated altitude for SL34
1	Ozone Coffee8	1,500–2,100 m
2	Roastopedia2	1,500–2,100 m
3	Volcana Coffee9	1,300–2,000 m
4	Bean Brew Digest6	1,600–2,100 m, best expression 1,750–1,950 m

All four were read directly. The overlap — roughly 1,600–2,000 m — is where every source agrees SL34 works, and that sits inside the range this wiki’s Kenya note treats as normal for the country, so none of this is specific to the variety rather than to the origin.

The one genuinely variety-specific claim in that table is Volcana’s: SL34 “tolerates wetter, lower conditions than SL28”.⁹ That fits WCR’s framing of SL34 as wanting good rainfall while SL28 is the drought-tolerant one, and it is the practical reason a Kenyan farm might plant SL34 on its damper, lower blocks. It is still a single roaster-facing source, so read it as a rule of thumb.

On water and soil, Roastopedia is the only source consulted that gives numbers: SL34 “requires a well-distributed annual rainfall pattern exceeding 1,200 millimetres and thrives in deep, well-drained, acidic volcanic soils rich in organic matter” — confirmed by reading the page.² The soil description is a fair account of central Kenya’s growing conditions generally; whether SL34 specifically needs it more than any other Arabica is not something that source demonstrates.

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”. 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”¹⁰ — 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”.¹¹ 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. 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.¹² 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, and WCR’s own trait tables record exactly that split.

Two caveats, both added, 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. 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. MTPak Coffee ties SL34 to Kenya’s broader reputation for “a rich body, bright acidity, and distinctive berry undertones”. Ulu Coffee’s own note on their trees is shorter: “complex acidity, full mouthfeel, fruity flavors.” Volcana Coffee lands in the same place with fewer words — “dark fruit, heavy sweet body, bright citrus finish” — confirmed by reading that page.⁹ Across every description consulted, the two constants are dark fruit and a heavy, sweet body; what varies is whether the writer hears the acidity as winey, malic or citric.

The most useful description is the one that puts SL34 next to SL28 rather than on its own, since that is the only comparison a buyer ever actually makes. Morning Wines sets SL28’s “distinct fruit-forward acidity, pronounced sweetness, and long, elegant finish” against SL34’s “fuller body, caramel sweetness, and a less sharp, though equally vibrant, acidity” — confirmed by reading that page.³ In one line: SL28 is the sharper cup, SL34 the rounder and sweeter one. Treat that as one educator’s framing, not a measured difference — no controlled sensory comparison of the two varieties was located, and in Kenya they are usually blended together anyway, so very few people have tasted them side by side.

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.

One source does give numbers, and they should not be repeated as fact. Bean Brew Digest states that “a 2022 Q Grade report from the Coffee Quality Institute recorded an average score of 87.3 for 42 SL34 samples submitted from central Kenya,” and tabulates individual lots including Gichathaini Washing Station in Nyeri at 1,840 m, scored 88.2 — both confirmed by reading the page.⁶ The wording is specific enough to sound checkable, but no such CQI report was located, the page gives no link, document title or reference number for it, and CQI does not publish variety-level score averages of that kind anywhere this search could find. It is also the same source that places SL34’s origin on the wrong side of Kenya (see above), which is reason enough not to lean on it. Treat 87.3 and 88.2 as unsourced figures, not cupping records.

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.¹³ 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. 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”.⁶ 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.

Roastopedia puts a name on the same idea, writing that “SL34 belongs to the Typica-related genetic group, specifically aligning with the ‘Ethiopian Legacy’ cluster” — confirmed by reading the page.² The Typica half again matches WCR. The cluster name does not appear in WCR’s record or in any genetics publication located here, and no study is cited for it, so it is best read as that site’s own label rather than a term from the literature.

Related

• Kenya — the origin it was selected in and is almost entirely confined to
• SL28 — the stablemate it is always sold beside, and the one that really is a Bourbon
• SL14 — the third Scott Labs selection in WCR’s catalogue, also Typica-related, but rated only “Good” in the cup
• 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
• Coffee Quality Institute — the body credited with an SL34 score average this note could not confirm exists
• Geisha — the other variety whose reputation rests almost entirely on the cup

Official links

• Official site — World Coffee Research variety record: SL34
• Official site — World Coffee Research

Footnotes

1. Green Coffee Collective — SL-34: Kenya’s fruit-forward Scott Labs variety ↩

2. Roastopedia — SL34 coffee: history, characteristics, cultivation, flavor ↩ ↩² ↩³ ↩⁴ ↩⁵

3. Morning Wines — SL28 & SL34: Kenya’s legendary cultivars ↩ ↩²

4. World Coffee Research — SL14 ↩

5. Ulu Coffee Farm — Kona Typica, SL-34 and Gesha ↩

6. Bean Brew Digest — SL34 variety genetics and flavor ↩ ↩² ↩³ ↩⁴

7. World Coffee Research — SL34 ↩

8. Ozone Coffee — SL34 coffee varietal: Kenya’s Typica mystery ↩ ↩²

9. Volcana Coffee — SL34 coffee variety: origins, agronomics & cup profile ↩ ↩² ↩³

10. Perfect Daily Grind — Exploring popular Kenyan coffee varieties: SL-28 & SL-34 ↩

11. World Coffee Research — SL28 ↩

12. MTPak Coffee — SL28 and SL34: a coffee roaster’s guide ↩

13. Hydrangea Coffee — SL34 hybrid washed, Café Granja La Esperanza ↩