In anaerobic fermentation, coffee cherries or beans are fermented in sealed tanks without oxygen. This produces particularly intense, often tropical-fruity or winey aromas.

What Is Anaerobic Fermentation in Coffee?

In anaerobic fermentation, coffee cherries or beans are fermented in sealed tanks without oxygen. This produces particularly intense, often tropical-fruity or winey aromas.

Why that matters

Anaerobic fermentation is one of the most exciting developments in coffee processing in recent years. The idea comes from winemaking: when fermentation takes place without oxygen, different aromatic compounds form than in conventional aerobic fermentation.

The process: harvested cherries (or already depulped beans) are placed in airtight steel tanks or plastic containers. The containers are sealed and fitted with a one-way valve that lets CO₂ escape but prevents oxygen from entering. In this oxygen-free environment, anaerobic bacteria and yeasts take over the fermentation — different microorganisms than in classic processing.

Fermentation duration varies widely: from 24 hours to several weeks. Temperature, pH, and pressure are monitored. Some processors add fruits, spices, or yeasts to create specific flavour profiles — so-called “infused” or “co-fermented” coffees.

The result can be spectacular: intense tropical fruits, wine-like aromas, cinnamon, rum — profiles that would be impossible with classic processing. The best anaerobically fermented coffees achieve top placements and record prices at competitions.

The method is also controversial. Critics in the specialty scene argue that overly intense fermentation masks the character of the bean — you taste the process, not the coffee. Others see it as the future of coffee processing. The debate echoes the discussion around barrel ageing in winemaking: how much process influence is desirable?

At Green Wall Coffee

At our café on Sophienstraße 27 in Berlin-Lichtenberg, we occasionally offer anaerobically fermented coffees — when the flavour complements the bean rather than overpowering it. At the counter, I tell guests honestly: anaerobically fermented coffee isn’t for everyone. Some love the intense fruit aromas, others find them too much. It’s worth trying either way.

Related Questions

• What is washed processing?
• What is natural processing?
• What is honey process and what variants exist?

More depth on this topic in the article How to Make Perfect Espresso. Or stop by at Sophienstraße 27 — Mon–Fri 8am–5pm, Sat 10am–5pm.