Anaerobic Fermentation Coffee: What It Is & Why It Tastes So Different
Key Takeaways
- Anaerobic fermentation seals coffee cherries or depulped beans in oxygen-free tanks, allowing lactic acid bacteria to dominate fermentation and produce distinctly different flavor compounds than traditional aerobic processing
- The process creates intense, unusual flavors — tropical fruit, fermented sweetness, cinnamon, and sometimes wine or whiskey notes — that are polarizing among coffee drinkers
- Anaerobic processing requires precise temperature control and careful management; poorly executed lots can produce defective, vinegar-like flavors
In 2015, Colombian producer Camilo Merizalde introduced anaerobic processing at the World Barista Championship. The unusual fermented, cinnamon-and-tropical-fruit flavors in his coffee shocked judges and ignited a global conversation that continues today.
Anaerobic fermentation is now one of the most discussed — and most divisive — trends in specialty coffee.
What Is Anaerobic Fermentation?
Standard coffee fermentation (in washed processing) happens aerobically — in open tanks or on raised beds where oxygen is present. Aerobic fermentation is dominated by wild yeasts and bacteria that produce the characteristic bright, clean acids of traditional washed coffee.
Anaerobic fermentation changes one fundamental variable: oxygen is removed.
Cherries or depulped beans are sealed in airtight stainless steel tanks with a one-way CO₂ release valve. Without oxygen:
- Aerobic bacteria and yeasts cannot thrive
- Lactic acid bacteria (LAB) dominate the fermentation
- Fermentation chemistry shifts dramatically, producing different organic acids and esters
- The CO₂ produced by fermentation builds up inside the tank (and escapes through the valve)
The Science Behind the Flavor
According to research published through the SCA and independent studies, anaerobic fermentation produces elevated levels of:
- Lactic acid: Creates a creamy, yogurt-like roundness
- Ethyl acetate: Fruity, wine-like compound
- Complex esters: Tropical fruit, bubble gum, cinnamon
- Succinic acid: Adds sweetness and body
The result is a flavor profile that can include:
- Intense tropical fruit (passionfruit, mango, lychee)
- Cinnamon and exotic spice
- Fermented sweetness (wine, sake, berry)
- Sometimes: whiskey, rum, or other aged beverage notes
Anaerobic processing requires strict temperature control. Fermentation that runs too warm or too long produces acetic acid (vinegar) and other off-flavors. The difference between an exceptional anaerobic lot and a defective one often comes down to 2°C and a few hours of fermentation time.
Variants of Anaerobic Processing
Anaerobic Natural
Whole cherries (with skin and pulp intact) are sealed in tanks. Maximum fruit sugar contact, most intense flavors.
Anaerobic Washed
Depulped beans (mucilage intact) ferment anaerobically, then are washed. Cleaner than anaerobic natural but still has unusual fermentation character.
Carbonic Maceration (CM)
Borrowed directly from wine production (Beaujolais method). Whole, intact cherries ferment in CO₂-saturated tanks. Produces particularly vivid, candy-like fruit flavors.
Lactic Fermentation
Controlled temperature (around 15°C) promotes lactic acid bacteria specifically, producing creamy, yogurt-like roundness.
The Controversy
Anaerobic processing divides the coffee world:
Proponents argue:
- It dramatically expands coffee's flavor vocabulary
- Allows producers to differentiate their lots in competitive markets
- Demonstrates the breadth of what coffee can be
Critics argue:
- Heavy processing masks terroir — you're tasting the process, not the origin
- Inconsistency: even experienced producers get defective lots
- "Coffee should taste like coffee, not tropical punch"
The specialty community has not reached consensus. Some of the world's top baristas and roasters champion anaerobic processing; others refuse to work with it.
Who Should Try Anaerobic Coffee
Try it if you:
- Enjoy wine, sake, or craft beverages with complex fermented flavors
- Want to experience the extreme edge of specialty coffee
- Are curious about unusual flavor profiles
Avoid it if you:
- Prefer clean, transparent origin character
- Dislike fermented or vinegary off-flavors (be cautious with sources)
- Find fruity coffee already "too different" from traditional coffee
Brewing Anaerobic Coffee
Anaerobic coffees are often best brewed with methods that preserve their intensity:
- Pour-over at lower temperature (87–90°C): Prevents over-extraction of heavy flavor compounds
- French Press: Amplifies the body and tropical fruit
- Avoid espresso for first-timers: The intensity can be overwhelming
When trying anaerobic coffee for the first time, brew it alongside a traditional washed coffee from a similar origin. The contrast between the clean washed cup and the anaerobic's fermented complexity makes both coffees more understandable — and helps you decide which style you prefer.
Summary
Anaerobic fermentation is one of specialty coffee's most radical innovations, producing flavors that challenge assumptions about what coffee can taste like.
Key takeaways:
- Anaerobic processing seals beans in oxygen-free tanks, allowing lactic acid bacteria to dominate and produce unusual flavor compounds
- The resulting flavors — tropical fruit, cinnamon, wine-like sweetness — are intentional and can be extraordinary when done well
- Quality is highly variable; source from reputable producers to avoid defective lots
- Start with pour-over at 87–90°C and compare side-by-side with a traditional washed coffee
About the Author
Coffee Guide Editorial
A team of writers and baristas passionate about coffee. We cover everything from bean selection and brewing methods to café culture.
Team Credentials
- Certified baristas
- Specialty roasting café experience
- Coffee import industry experience