Processing method
Anaerobic Fermentation
A modern, experimental method that ferments coffee in sealed, oxygen-free tanks to build bold, distinctive flavors.
What is anaerobic fermentation?
Anaerobic processing means fermenting coffee without oxygen. Cherries (or depulped seeds) are sealed inside airtight tanks, often purged with CO₂, where a different cast of microbes takes over than in an open-air ferment. Producers can control time, temperature, pH, and even add fruit or specific yeasts.
The technique is borrowed from wine — a sealed-cherry version is essentially carbonic maceration. It only went mainstream in specialty coffee in the 2010s, and it's now a fixture of competition lots and experimental micro-lots.
Step by step
- Harvest ripe cherries — sugar content and ripeness matter even more here.
- Seal the tank — cherries or seeds go into an airtight vessel; oxygen is displaced, usually with CO₂.
- Controlled ferment — held for 24–120 hours, with temperature and pH monitored closely.
- Process out — the lot is then finished as a washed, honey, or natural coffee (dried with or without its fruit).
- Dry & hull — dried to ~11% moisture, then milled.
What it tastes like
Anaerobic lots are intense and unmistakable — expect amplified fruit, tropical and boozy notes, warming spice like cinnamon, and a thick, syrupy body. The flavors can be polarizing: fans love the wild, fermented character; critics find aggressive lots taste more of the process than the origin.
Where you'll find it
It's a producer's technique rather than a regional tradition, so it turns up wherever growers chase distinctive lots — Colombia, Costa Rica, and Panama are especially associated with it, alongside award-winning micro-lots worldwide.