Why Is Black Coffee Sour? Is It Difficult to Accept? The Unique Berry Acidity of Kenyan Coffee

Understanding Coffee Acidity

When coffee professionals talk about the "acidity" of a coffee, they mean a vibrant, bright, fresh, and crisp sensation. Acidity is the single most important dimension of coffee tasting: without it, a coffee tastes hollow, flat, and lifeless.

As you slurp during a cupping, the liquid spreads across the tongue's four types of taste receptors — sour, bitter, sweet, and salty — and a gentle acidity registers along the sides and back of the tongue. Coffee acidity is generally treated as a marker of quality. It is the hallmark of high-value coffees from Central America and East Africa, while outright sourness is considered a defect. Acidity is associated with coffee grown at high altitude, in mineral-rich volcanic soil.

Acidity also takes many different forms, which makes it a key clue for telling origins apart. Coffee from Yemen or East Africa tends toward striking fruity aromatics and a red-wine-like texture, while many high-grown Central American or Caribbean coffees show what cuppers call bright acidity.

Washed beans carry higher perceived acidity than natural (dry-processed) beans — naturals are denser and more concentrated, and that concentration masks acidity. The acids in the final brew also depend heavily on roast degree, roasting method, and brewing approach. pH matters too: a good cup of coffee should ideally land between 4.9 and 5.2.

Kenya Dormans Mill Washed

Kenyan coffee is world-famous for its distinctive berry aromatics, and that instantly recognizable character is thanks to Scott Laboratories, which spent years breeding the outstanding SL28 and SL34 varieties. This lot uses fully ripe SL28 grown in the 2,000-meter high-altitude zone of Mount Kenya, processed at the renowned Dormans Mill through Kenya's signature 72-hour double-fermentation washed method, then shaped by our roasting team into a charming cup with a dark plum juice finish — a tasting experience all its own.

Coffee Details

Region: Kirinyaga, Dormans Mill

Altitude: 1670-1980m

Processing: K72 Washed (Kenya's characteristic double-fermentation washed process)

Variety: SL28 (the variety that made Kenya world-famous)

Grade: AB (premium grade)

Flavor: Bright grapefruit entry, sweet-sour black plum, full honey sweetness, thick texture, aged tangerine peel, kumquat, blueberry, dark plum juice, and a blackcurrant aftertaste

In brief: FrontStreet Coffee is a specialty coffee research shop, glad to share coffee knowledge with everyone. We share without reservation to help more people fall in love with coffee — that has been our mission for the past 6 years.

FrontStreet Coffee Recommendation

Kenya is the undisputed master of washed processing, and FrontStreet Coffee's Kenya "Cherry Tomato" is one of its best-known ambassadors. The lot is washed twice — flotation, pulping, fermentation soaking, and repeated rinses — so the juiciness of the fruit comes through at full force.

In the cup you get rich aromas of cherry tomato, dark plum, snow pear, black plum, and yellow sugar: sweet-sour, dripping with juice, and beautifully clean. If the K72 Dormans lot above caught your attention, this is the one to queue up next.