Anaerobic fermentation ferments coffee cherries in sealed tanks without oxygen, usually with a valve to release CO₂.
What changes
Excluding oxygen changes which microbes dominate and which compounds they produce. Fermentation is slower, more controlled, and produces results that traditional open fermentation cannot.
Producers can also control temperature, duration, and sometimes add specific yeast cultures.
What it tastes like
Intense and unusual: tropical fruit, cinnamon, rum, red wine, bubblegum, fermented berry. Often far more aromatic than the same coffee processed conventionally.
At its best, extraordinary. At its worst, it tastes of the process rather than the coffee — boozy, solventy, homogenised.
Carbonic maceration
A related technique borrowed from winemaking: whole cherries in a CO₂-flooded tank, so fermentation happens inside the intact fruit.
Why it is controversial
The criticism is that it overwrites terroir. If a Colombian and an Ethiopian both taste of cinnamon and rum after the same anaerobic protocol, the process has erased the place.
The defence is that it is a legitimate craft choice, that it can raise the value of ordinary lots dramatically, and that producers deserve that option.
Buying one
Treat it as a distinct category, not as a better version of a normal coffee. Brew it cleanly — filter, black — and expect something loud.
Last reviewed 8 August 2026