Kirinyaga County sits within Kenya's coffee heartland, and Mamuto farm at 1,524 meters represents the lower altitude end of the Kenyan specialty range — just inside the SHB threshold where density and soluble concentration reach specialty grade. The 200-meter gap between this farm and the highest-altitude Kenyans in this batch is measurable in extraction behavior: altitude explains roughly 25% of variation in extraction yield, and at 1,524 meters you're working with a slightly lower soluble ceiling than a 1,700 or 1,725-meter equivalent.
SL28 here carries no blended SL34 component — it's a single-variety lot, which means the flavor profile reflects SL28's genetic character without the slight softening SL34 brings. Scott Laboratories bred SL28 for the Kenyan highlands from drought-tolerant Tanganyika stock. Its genetic lineage is Bourbon-related (the WCR classification places it in the Bourbon-Typica group), which means it follows Bourbon-group roast behavior: high density, slow path to first crack, needs full MAI phase development to express its acid and body potential. At light roast, that development window produces the blackcurrant and intense citrus character SL28 is known for — driven by citric acid concentration that consistently exceeds its sensory detection threshold in the cup.
Washed processing strips the fruit layer entirely, leaving terroir and varietal chemistry unobscured. The light roast preserves high chlorogenic acid levels for brightness while stopping before the CGA-to-quinic-acid decomposition cascade produces bitterness. What you're left with is what SL28 actually tastes like when grown in Kenyan volcanic soil and left to express itself through washed processing — the origin's character without fermentation additives or roast-level modifications layered on top.
Mamuto AA scores 96/100 on Chemex, and the match is about managing SL28's structural acidity through maximum filtration clarity. SL28 produces exceptionally bright acidity — this is the variety's defining chemical characteristic. The Chemex's thick paper filter removes essentially all coffee oils plus the fine particles that would add textural interference to the acid structure. The grind is set at 480μm, 70μm finer than default — significantly tighter than a standard Kenyan setup, because SL28's high density at 1,524 meters means even harder cells requiring more surface area for extraction. The 94°C temperature and 1:15–1:16 ratio create conditions where blackcurrant and citrus compounds can fully develop without crossing into aggressive sourness. The Chemex's longer drawdown relative to V60 extends contact time, compensating for the finer grind and pulling the slow-extracting sweet compounds that balance SL28's acid.
Troubleshooting
sour: Grind finer by ~22μm and raise temp to 95°C. SL28's citric acid is present at levels above detection threshold by design — the issue is insufficient extraction of the sweet Maillard and caramelization compounds that provide balance. Finer grind and higher temp accelerate access to those compounds through SL28's dense cell walls.
thin: Increase dose by 1g or reduce water by 15g; consider a metal filter. SL28's exceptional cup quality at altitude comes with low yield and lower melanoidin potential at light roast — TDS can land below target even with correct extraction yield. A metal filter retains oils that partially compensate for the lighter body.
The V60 at 88/100 is the fastest-draining of the three pour-overs, and for Mamuto's SL28 this creates the critical trade-off: the V60's speed favors brightness and acid clarity — exactly what SL28 delivers — but the short contact window is unforgiving if the grind is even slightly coarse. The recipe sets the grind at 430μm — 70μm finer than default — driven primarily by the light roast's low solubility. Dense, light-roasted beans need significantly more surface area for the water to extract properly within the V60's typical 2:30–3:30 window. With Kenyan SL28, full extraction is essential: the variety's intense citric acidity must be thoroughly extracted to transform from aggressive sourness into balanced blackcurrant brightness. At 94°C, the full default temperature ensures enough thermal energy to push through this dense 1,524-meter bean without any processing-related sensitivity holding it back.
Troubleshooting
sour: Grind finer by ~22μm and raise temp to 95°C. At 430μm, SL28 extracts faster than most light roasts — but fast doesn't mean complete. If the shot tastes aggressively sour rather than bright, extraction is still running short of the sweet compounds. The V60's faster drain makes this more likely; slow your pour to extend contact time.
thin: Increase dose by 1g or reduce water by 15g; a metal filter helps. SL28 is rated low yield agronomically, and its light roast produces fewer melanoidins than heavier-developed roasts. The V60 paper filter compounds this — the cup can be texturally light even when extraction yield is correct.
The Kalita Wave's flat-bed geometry is particularly valuable for Mamuto's SL28 because it enforces the even extraction that SL28 demands. SL28's intense acidity creates a steep gradient between underextracted (aggressively sour blackcurrant) and properly extracted (bright, complex, balanced) — this is why even water distribution matters so much. The Kalita's three-hole drain and flat bed mean water distributes evenly across all grounds rather than channeling toward a single center point, reducing the variance in particle extraction that produces simultaneous sour-and-sweet. The grind at 460μm is 30μm coarser than the V60 setting but 70μm finer than default, reflecting the Kalita's slower drain relative to V60 — slightly coarser is appropriate when contact time is longer. The 1:16–1:17 ratio is the leanest among the three pour-overs, which compensates for the extended contact time.
Troubleshooting
sour: Grind finer by ~22μm and raise temp to 95°C. The Kalita is more forgiving than the V60 but SL28 at light roast is still the most demanding grind calibration in this batch — the variety's citric acid concentration means underextraction reads distinctly sour rather than subtly unbalanced. Don't pour on the filter walls; uneven wetting disrupts the flat bed.
thin: Increase dose by 1g or reduce water by 15g; consider metal Kalita filter for body. Mamuto's single-variety SL28 lot has lower yield than most specialty varieties — less mass in the bed means less material to extract. The paper filter removes the oils that would add weight, leaving a cup that can read watery at low doses.
The AeroPress at 85°C handles Mamuto's SL28 differently than the pour-overs, and the lower temperature is the critical variable. SL28 produces exceptionally bright acidity — brew at 94°C under pressure and you risk extracting bitter compounds from roast development alongside the acid, creating harshness that competes with the blackcurrant character. At 85°C, citric acid's solubility decreases slightly and extraction of bitter polyphenols is slower, giving the sweet Maillard compounds more relative weight in the extraction. The grind at 330μm is 70μm finer than the V60, which compensates for the lower temperature by increasing surface area. The AeroPress immersion phase — grounds fully submerged before pressing — gives SL28's dense structure more saturation time than a continuous pour, partially replacing the extraction energy that lower temperature removes.
Troubleshooting
sour: Grind finer by ~22μm and raise temp to 86°C. SL28's citric acid extracts rapidly at any temperature; the challenge is extracting enough balancing compounds before pressing. If sour, extend the steep time by 20–30 seconds before plunging — more contact time at 85°C gets you past the acid phase without the bitterness risk of higher temperatures.
thin: Increase dose by 1g or reduce water by 15g. The AeroPress paper filter at 85°C removes oils and slows extraction simultaneously — both reduce body. For SL28, where cup quality is in the acid-sweetness balance rather than body weight, thin often means insufficient dose rather than a filter or temperature problem.
The Clever Dripper's immersion design gives Mamuto's SL28 something the pour-overs don't: complete saturation of the coffee bed before any water exits. This matters for SL28 specifically because the variety's exceptional cup quality depends on extracting through all layers of a dense high-altitude Kenyan bean evenly — and the Clever Dripper's submerged steep period ensures every particle contacts water simultaneously. The grind at 460μm matches the Kalita Wave setting — the same logic applies: slightly coarser than V60 to account for extended contact time. The recipe tightens the grind 70μm below default to ensure adequate extraction through the steep, compensating for SL28's high density. At 94°C with 3–4 minutes of immersion, the Clever Dripper gives SL28 enough thermal energy and contact time to pull past the acid phase into the blackcurrant and citrus sweet spot that defines this variety's character.
Troubleshooting
sour: Grind finer by ~22μm and raise temp to 95°C. Even with immersion, SL28 at light roast can underextract if steep time is on the low end of the 3–4 minute range. If the cup is sour, extend to the 4-minute mark and go finer — the Clever Dripper's flat paper filter is less restrictive than Chemex, so there's headroom to tighten the grind.
thin: Increase dose by 1g or reduce water by 15g; try a metal filter insert. SL28's low agronomic yield means less mass per cherry — the bean doesn't pack as much extractable material per gram as higher-yield varieties. Metal filter retains oils that paper strips, adding body that this single-variety Kenyan lot lacks at light roast.
Mamuto AA espresso presents the most demanding extraction scenario: SL28 produces some of the most intense acidity in specialty coffee, and concentrating it at 9 bar to a 1:1.9–1:2.9 ratio amplifies every compound in the extraction. The grind at 180μm is 70μm finer than the espresso default — reflecting both the light roast's lower solubility and SL28's extreme density from Kenyan highlands growing conditions. At this fineness, puck resistance is high enough to slow water velocity and extend the extraction window, critical for pushing past SL28's dominant citric acid phase into the sweeter compounds. Preinfusion is essential — soaking the puck before full pressure reduces channeling through the ultra-fine, ultra-dense light roast puck. Expect shots that are bright, fruit-forward, and potentially wine-like when extraction is correct.
Troubleshooting
sour: Grind finer by ~10μm and raise temp to 94°C. SL28 at 180μm is already approaching the fine end; tighten carefully. Sour SL28 espresso means extraction ran fast through the acid phase. The 1°C temperature increase accelerates diffusion through the dense Kenyan cell structure. Extend preinfusion time to 8–10 seconds if available.
thin: Increase dose by 1g or reduce water by 15g. Light roast SL28 has lower available solubles than medium-developed Kenyan — the TDS ceiling is physically lower. If running to ratio but thin, the dose needs to increase. Verify the puck isn't channeling — channeled shots at this ratio produce thin AND sour simultaneously.
The moka pot concentrates Mamuto's SL28 to 1:9–1:10 ratio, and at light roast the flavor is intense by any measure. The grind is set at 280μm, 70μm finer than default — the tightest moka pot grind you'll see for this roast level — because SL28's density requires the extra surface area to extract through at 1.5 bar pressure. The pre-boiled water technique is especially important here: cold-start moka brewing develops sourness in SL28 as the ground heats slowly through the acid extraction phase before pressure builds. With pre-boiled water, the extraction begins at full temperature immediately, skipping the cold acid phase. The resulting concentrated brew from a properly extracted Mamuto SL28 moka pot should show intense blackcurrant and citrus without the harsh sourness that characterizes underextracted high-acid Kenyan concentrates.
Troubleshooting
sour: Grind finer by ~22μm and use pre-boiled water. SL28's high citric acid concentration makes it the most sour-prone bean in this batch when moka pot extraction is incomplete. Cold-start moka brewing is the most common cause — the slow heat-up phase extracts acids preferentially. Pre-boiling eliminates that cold phase entirely.
thin: Increase dose by 1g or reduce water by 15g. SL28's light roast has lower solubility — the moka pot's 1.5 bar pressure can't compensate for insufficient dose mass the way 9-bar espresso can. Pack the basket as full as the recipe allows without tamping.
strong: Reduce dose by 1g or add 15g water. Moka pot concentration with SL28 can tip into overwhelming brightness if the ratio is too tight — the citric acid intensity that reads as complex balance at 1:9 becomes harsh at 1:8. Slightly more water in the base dilutes without changing extraction dynamics.
French press scores 76/100 for Mamuto's SL28, and the reason is mechanical: French press is unfiltered, so oils and fines pass through into the cup. For most beans, retained oils add welcome body. For SL28 at light roast, the problem is that the metal filter also passes ultra-fine particles that overextract, turning SL28's bright citrus into harsh, astringent sourness. The recipe compensates with 96°C water and a 930μm grind 70μm finer than default. The higher temperature drives extraction through the coarse particles before sourness from fines can dominate; the finer grind (for French press) increases overall extraction. The wide time window (4–8 minutes) reflects the tension: Hoffmann's extended steep allows grounds to settle, but SL28 benefits from the shorter end to avoid fines overextraction.
Troubleshooting
sour: Grind finer by ~22μm and steep at the higher end of the 4–8 minute window. For SL28 in a French press, sourness means underextraction of the coarse particles — the fines likely extracted fine, which is why the cup isn't just thin. Finer grind brings the coarse particles up to extraction level while the extended steep time completes the process.
thin: Increase dose by 1g or reduce water by 15g. French press body from SL28 comes from oils — the metal filter lets them through. If the cup is thin, the issue is insufficient concentration, not filtration. SL28's low agronomic yield means lower mass per volume; bump the dose before adjusting grind.
Cold BrewFlash Brew Recommended
Cold brew is not recommended for this bean. At near-freezing temperatures, cold water cannot extract the complex acids, delicate aromatics, and bright fruit compounds that define a light-roasted coffee — they remain locked in the cell matrix. For a cold version of this coffee, use flash brew: brew a concentrated pour-over (V60 or Chemex at 60% of the normal water volume) directly over ice in the server. The hot water extracts the full flavor spectrum, and the rapid ice cooling locks in volatiles that would otherwise evaporate during a slow cool-down.