The AA and AB designations in Kenyan grading refer to screen size — AA is the largest beans, AB is slightly smaller. Both come from the same Mamuto farm, the same producer, the same variety (SL28), the same altitude (1,524m), the same processing. The only difference between this lot and the Mamuto AA is roast level: this one is medium rather than light.
That one variable changes the chemistry substantially. At medium roast, the chlorogenic acids that drive Kenyan brightness have partially decomposed into quinic acid. Quinic is bitter and astringent — the same compound that builds up in stale coffee on a hot plate. Medium development doesn't eliminate the pleasant citric and malic acids, but it reduces their dominance. In their place, Maillard products push forward: melanoidins build body, and caramelization products produce the chocolate and caramel notes that medium roast Kenyans are prized for by a different segment of coffee drinkers.
SL28 follows Bourbon-group roasting behavior — slower to first crack, higher density — which means a medium roast on this variety produces heavier Maillard development than a lighter Brazilian variety at the same nominal roast level. The melanoidin content at medium roast runs toward 10 to 18% of roasted dry weight, contributing the syrupy mouthfeel that lower-roast Kenyans lack.
The tradeoff is predictable. Sucrose is nearly 100% consumed during roasting regardless of level, but perceived sweetness is aroma-mediated — at medium development, caramelization products like furanones and maltol create the olfactory sweetness signal your brain interprets as sweet. The brighter, more volatile citrus esters present in the light-roasted AA are largely gone here. The structural complexity of [Kenyan SL28](/blog/kenyan-coffee-flavor-notes-and-best-coffees) remains, but it expresses through a different chemical vocabulary.
The AeroPress recipe for Mamuto AB Medium runs at 400μm — with no altitude-based grind adjustment for this bean since SL28 at 1,524m sits at a moderate density threshold. The extraction characteristics are driven primarily by roast level: the 83°C temperature reflects the medium roast's higher solubility. At 400μm versus the finer grinds needed for denser high-altitude beans, the coarser setting reflects SL28's medium density — it extracts adequately without the extra fineness that very high density beans require. Immersion contact time in AeroPress means this difference is largely self-correcting, but the grind point matters for pressure consistency during the plunge.
Troubleshooting
bitter: Grind coarser by ~22μm and decrease temp by 1°C, to 82°C. Medium-roasted SL28 carries more CGA decomposition products (quinic acid) than light roast — the AeroPress's full immersion at 83°C extracts these efficiently. If your plunge is slow or steep time exceeds 2 minutes, bitterness builds from this fraction.
thin: Increase dose by 1g or reduce water by 15g; switch to metal filter. AeroPress paper strips melanoidin oils from this medium-roasted Kenyan SL28. Medium roast built those oils via extended Maillard phase — metal filter preserves them and delivers the syrupy mouthfeel the narrative describes.
Mamuto AB Medium at 530μm in the Clever Dripper (the same coarser endpoint as Kalita Wave) reflects SL28's large bean size and moderate density. The immersion phase is the key advantage here: SL28's large bean structure holds Maillard compounds that medium development built, and immersion time allows those compounds to fully dissolve without requiring a specific pour technique. The paper filter then removes the bitter sediment and fines that might otherwise add astringency — particularly relevant for medium-roasted Kenyan SL28, where bitter compounds from roast development accumulation from the breakdown of bitter precursors during roasting is higher than at light roast. The Clever Dripper bridges French press extraction completeness and filtered cup clarity in a way that suits this specific bean's medium-roast chemistry.
Troubleshooting
bitter: Grind coarser by ~22μm and decrease temp by 1°C. The Clever Dripper's immersion phase extracts quinic acid — the CGA decomposition product that medium roast generates on Kenyan SL28 — efficiently at 92°C. If steep runs to the 4-minute end, bitterness can build. Reduce to 3 minutes at the coarser grind.
thin: Increase dose by 1g or reduce water by 15g. SL28 at medium density needs proper ratio support in the Clever Dripper's paper-filtered output. The immersion phase extracts thoroughly, so thin cups are a ratio issue — the paper filter removes body-contributing oils that you compensate for with concentration.
SL28 at medium roast on the V60 sits in a specific extraction territory: the variety's Bourbon-group genetics mean it roasts like Bourbon (slow to first crack, heavy Maillard development), but its Kenyan origin and legendary quality classification mean the underlying acid structure is more complex than most Bourbon-group origins. Medium development shifts CGA-driven Kenyan brightness toward bitter compounds from roast development and Maillard complexity — in the V60, the technique-dependent conical flow means the quality of your pour directly controls how much of that shifted flavor profile you capture. At 500μm and 92°C, this recipe runs coarser than typical for high-altitude lots at this roast level. SL28's large bean size and medium density means it doesn't need the same grind compensation as denser, higher-altitude beans.
Troubleshooting
sour: Grind finer by ~22μm and increase temp by 1°C. SL28 at medium roast still retains significant citric and malic acid structure — at 500μm, if pour technique is inconsistent and contact time drops, you extract the acids before the Maillard compounds. Swirl after each pour to maintain even bed saturation.
thin: Increase dose by 1g or reduce water by 15g; try a metal filter. SL28's medium density means it extracts less aggressively than very high density Bourbon at 2,000m+ — thin cups are more likely to be a ratio issue than a technique issue. Metal filter passes melanoidin oils for more body.
The Kalita Wave's flat-bottom bed and three-hole restriction create even extraction that suits this SL28 Kenyan well. At 530μm — the Kalita default for this roast level — the flat bed provides consistent contact across the entire coffee bed, avoiding the channeling risks of a cone dripper. The temperature at 92°C (2°C below the Kalita default) accounts for medium roast's improved solubility, pulling back heat slightly to avoid over-extracting the berry and citrus character. At 1:17 ratio, the pulse-pour method (100g bloom then five 50g pulses) controls flow rate through the flat bed. SL28's single-variety composition means uniform density throughout the bed — every particle extracts at the same rate, which is exactly what the Wave's even geometry is designed to exploit.
Troubleshooting
sour: Grind finer by ~22μm and increase temp by 1°C. SL28's large bean size means the flat bed packs with more interstitial space than average — if flow rate is fast despite 530μm, water bypasses grounds. Finer grind tightens the bed and restores contact time needed for Maillard compound dissolution.
thin: Increase dose by 1g or reduce water by 15g. Medium-roasted SL28 at 1,524m has moderate density — it won't over-extract easily, so a slightly tighter ratio is straightforward. The Kalita Wave's consistent extraction means the fix is in the ratio, not technique.
The Chemex produces its most distinctive effect on medium-roasted Kenyan SL28: the variety's exceptional quality rating (WCR: Exceptional at high altitude) at medium roast means the caramelization and Maillard compounds are worth showcasing, but the thick Chemex filter strips the oils that would add texture to that showcase. The result is the cleanest possible version of medium-roast Kenyan structure — full citric-plus-Maillard balance in the cup with minimal body weight. At 550μm (the coarsest grind for this bean's pour-over recipes), 92°C, and 1:16 ratio, this is a measured approach. The Chemex's 20-30% thicker filter also catches more SL28-derived fines than standard paper — SL28's large bean size can produce more fines distribution variation than smaller-bean varieties.
Troubleshooting
thin: Increase dose by 1g or reduce water by 15g. The Chemex filter removes oils from this medium-roasted Kenyan SL28, and unlike the light-roasted Mamuto AA which carries more volatile aromatics to compensate, the medium version relies on melanoidin body — exactly what the thick filter catches. Adjust ratio first.
sour: Grind finer by ~22μm and increase temp by 1°C. Chemex with SL28 at medium roast: if drawdown is running fast (under 3:30 total), water is bypassing the grounds. The thick filter can create uneven restriction — pour toward the center of the bed, avoid the sides where filter meets glass.
Espresso from medium-roasted Kenyan SL28 operates in an unusual flavor range: the pressure-concentrated cup amplifies the chocolate and caramel notes that medium development built, while also concentrating the bright acidity that SL28 retains even at medium roast. The 250μm grind (coarser than typical for high-altitude medium-roast lots, reflecting SL28's moderate density at this altitude) and 91°C temperature target a balanced 25-30 second shot. SL28's large bean size and medium density means the puck compacts somewhat differently than smaller-cell varieties — the 250μm point was calibrated for this. The recipe's 1:2 ratio produces a shot that showcases the chocolate-caramel range with enough acid structure to stay complex without aggressive sourness.
Troubleshooting
sour: Grind finer by ~10μm and increase temp by 1°C. Kenyan SL28's residual citric and malic acid profile at medium roast comes forward quickly under espresso's fast extraction. A sour shot means the puck flow rate is too high — 10μm matters significantly in espresso grind territory. Check puck preparation consistency too.
bitter: Grind coarser by ~10μm and decrease temp by 1°C. Medium-roasted SL28 carries more quinic acid than light roast — the CGA decomposition product that builds bitterness under pressure extraction. If the shot runs long or pulls hot, quinic acid dominates. Small adjustments have large effects at espresso grind settings.
The moka pot's 1.5 bar extraction from medium-roasted Kenyan SL28 produces a cup that sits between the espresso's intense concentration and the filter methods' cleaner clarity. Pre-boiled water prevents the slow-steam under-extraction problem that would strip only acids before pressure builds. At 350μm (coarser than typical for high-altitude medium-roast moka settings, reflecting SL28's moderate density) and 98°C water temperature in the base, the moka pot extracts the chocolate and caramel range that medium development built on SL28 without the sharp CGA-driven brightness that light-roasted Kenyan moka would show. The 1:10 ratio produces a concentrated serving — the medium roast's higher body from roast development versus the light roast means more body per gram in moka output.
Troubleshooting
sour: Grind finer by ~22μm and verify you're using pre-boiled water. Sour moka pot from medium-roasted Kenyan SL28 almost always points to the slow-heat extraction problem: without pre-boiled water, steam phases extract only the acid fraction before pressure develops. Pre-boiled water is the first fix.
strong: Reduce dose by 1g or increase water by 15g. Moka pot from medium-roasted SL28 runs strong because melanoidin content is higher than light roast and pressure extraction is efficient. The 1:10 ratio is already on the concentrated end — modest adjustment prevents overstrength while keeping structural weight.
French press is the only unfiltered method here, and for medium-roasted SL28 it delivers a specific cup characteristic: all the body-contributing oils stay in the cup, and the bitter compounds from roast development that medium development generates from the breakdown of bitter precursors during roasting — typically astringent in over-extraction — is held in check by the coarse 1,000μm grind and 94°C temperature profile. The high body of medium-roasted Kenyan SL28 in French press is notable: SL28 follows Bourbon roasting behavior (slower first crack, extended Maillard phase), and French press preserves every melanoidin that development produces. The 4:00-8:00 steep window allows flexibility; at 1,000μm, extending toward 8 minutes and then waiting for grounds to settle produces a cleaner result than a 4-minute plunge at the same grind.
Troubleshooting
strong: Reduce dose by 1g or increase water by 15g. French press TDS from medium-roasted SL28 runs higher than paper-filtered methods because oils and insoluble solids add to perceived strength. SL28's medium density extracts efficiently — a small ratio adjustment prevents overstrength without sacrificing the melanoidin body.
bitter: Grind coarser by ~22μm and decrease temp by 1°C. Bitterness in French press from this Kenyan medium is usually extended contact time amplifying quinic acid — the CGA decomposition product that builds during medium roast. Coarser grind and slightly lower temp reduce extraction rate without requiring shorter steep time.
Medium-roasted Kenyan SL28 in cold brew undergoes the largest flavor transformation of any method for this bean. The variety's reputation for blackcurrant, citrus, and intense acidity at light roast is already muted at medium roast — and cold water further suppresses the citric acid dominance (cold brew produces 28-50% fewer total acids than hot brew). What emerges is a smooth, low-acidity profile with chocolate and soft caramel character — entirely different from what SL28 is known for. At 900μm (coarser than typical cold brew settings for denser beans, reflecting SL28's moderate density at this altitude) and 1:7 concentrate ratio, the recipe accounts for this. The 12-18 hour steep range applies; research shows caffeine and CGA extraction plateaus around 7 hours, but the longer end of the range improves melanoidin dissolution for better body.
Troubleshooting
flat: Grind finer by ~22μm and steep at 4°C; check water mineral content. Medium-roasted SL28 cold brew can go flat because the variety's primary flavor contribution at medium roast — Maillard complexity — dissolves poorly in cold water. Minimally 150 ppm mineral water and slightly warmer steep temperature help.
thin: Increase dose by 1g or reduce water by 15g. Cold brew from medium-roasted SL28 loses the melanoidin body contribution that hot brewing would preserve — cold water extracts these compounds slowly. A stronger concentrate ratio directly addresses the thinness; dilute less aggressively when serving.