Anaerobic Natural
Anaerobic Natural ferments whole cherries in sealed tanks, blending natural body with intense anaerobic winey notes.
What Is Anaerobic Natural?
Anaerobic natural is one of specialty coffee's recent darlings. It adds a sealed fermentation step to the traditional natural process, letting microbes transform the fruit in an oxygen-free environment to create more complex flavor compounds. The method took off in the mid-2010s through barista competitions and competition lots.
How It Works
Coffee cherry pulp is rich in sugar. With oxygen present, fermentation is dominated by yeasts and acetic acid bacteria, which readily produce vinegary acetic acid. In a sealed, oxygen-poor environment, lactic acid bacteria and other anaerobic microbes dominate, producing lactic acid, esters and alcohols. By controlling time, temperature and pH, processors can steer toward a particular flavor direction.
Processing Steps
- Sort: float and hand-sort ripe red cherries of even ripeness after harvest
- Seal: place whole cherries in sealed barrels or stainless tanks
- Purge oxygen: a one-way valve lets fermentation CO2 push out oxygen, maintaining anaerobic conditions for 48–120 hours
- Monitor: track temperature, pH and sugar (Brix) to decide when to stop
- Slow drying: dry the whole fermented cherries slowly on raised beds, usually for 3–6 weeks
Flavor Profile
- A boozy bomb: rich rum, whiskey and ripe tropical fruit
- Layered complexity: pineapple, strawberry jam, cocoa and cinnamon are common
- Heavy body: an exceptionally round, oily mouthfeel
Risks and Debate
- Over-fermentation: poor control of time or temperature leads to vinegar, rotten fruit or nail-polish defects
- Flavor convergence: some argue strong fermentation flavors overwhelm origin and variety, making different coffees taste alike
- Higher cost: extra equipment, labor and monitoring usually mean higher prices
Notable Origins
- Colombia (e.g. Finca El Paraíso)
- Thailand (Chiang Mai)
- Costa Rica
- Panama and Ethiopia
Brewing Tips
Anaerobic naturals are usually roasted light to medium-light. For pour-over, slightly cooler water (88–92°C) rounds out sweetness and boozy notes; as cold brew or iced pour-over, the juicy, spirit-like character really stands out.