Anaerobic fermentation
also: anaerobic process, sealed fermentation
Fermenting cherries or beans in sealed, oxygen-limited tanks to build intense, funky, distinctive flavors.
Anaerobic fermentation ferments coffee in sealed, oxygen-restricted tanks, often plastic or steel vessels fitted with a one-way valve that lets CO2 escape but keeps air out. This can be done with whole cherries, with depulped beans, or as a stage layered onto a washed, natural, or honey workflow.
Why it matters: cutting off oxygen shifts which microbes dominate and slows the process, letting producers ferment longer and more controllably. The result is a distinctive, often loud flavor signature that has become a hallmark of experimental specialty coffee. Temperature, time, and pH are watched closely, since the same lever that creates clarity can tip into off-tastes.
In the cup, expect amplified sweetness and bold, sometimes wild notes: tropical fruit, fermented or boozy character, cinnamon and spice, even a syrupy body. Some drinkers love it; others find it overwhelming or disconnected from origin. Closely related is carbonic-maceration. See anaerobic-carbonic and fermentation for more.