Anaerobic Fermentation in Coffee (and How Carbonic Maceration Fits In)
Anaerobic processing has become one of the most talked-about methods in specialty coffee — often linked to intense tropical fruit, high sweetness, and sometimes winey or boozy notes. But the term “anaerobic coffee” is still widely misunderstood.
We’ll break down what anaerobic fermentation actually means, how it differs from other processing methods, and why carbonic maceration coffee tends to taste cleaner and brighter — even though it’s also anaerobic.
What does “anaerobic coffee” actually mean?
At its core, anaerobic simply means oxygen-free.
When a coffee is labelled as anaerobic, it refers to a fermentation stage that takes place in an environment where oxygen has been removed or excluded. This is typically done using sealed tanks, barrels, or sometimes plastic bags.
You’ll often see labels like:
- Anaerobic natural
- Anaerobic washed
- Anaerobic honey
These names describe what remains of the coffee cherry during fermentation, not the absence of oxygen itself.
Sugar is the fuel
Coffee is a fruit, and ripe coffee cherries contain a significant amount of sugar. During fermentation, this sugar becomes fuel for naturally occurring yeasts and bacteria.
As a general rule:
- More cherry = more sugar
- More sugar = more intense fermentation
This is why an anaerobic natural (fermented as a whole cherry) is often more aromatic and intense than an anaerobic washed coffee, where much of the fruit has been removed before fermentation.
What happens during anaerobic fermentation?
Once oxygen is depleted from the fermentation vessel, microbial activity shifts. Yeasts and bacteria begin feeding on available sugars and create a range of organic compounds, including:
- Lactic acid
- Alcohols
- Esters and other aromatic compounds
Well-executed anaerobic coffees often show high sweetness, layered tropical fruit, and a creamy, smooth acidity. More intense fermentations can lean winey, boozy, or funky — control is everything.
The final result depends heavily on fermentation time, temperature, microbial activity, and how much fruit remains on the coffee. Longer or less controlled fermentations tend to push intensity and funk, while tighter control often creates cleaner fruit expression.
Carbonic maceration: anaerobic, but more controlled
Carbonic maceration (CM) is also an anaerobic process — but it works slightly differently from what’s typically referred to as “classic” anaerobic fermentation.
Borrowed from winemaking, carbonic maceration in coffee involves fermenting whole cherries only inside a sealed tank that has been flushed with carbon dioxide (CO₂).
Secret ingredient: carbon dioxide
Carbon dioxide is heavier than oxygen. When CO₂ is introduced into a sealed fermentation tank, it physically forces oxygen out of the vessel. To make this possible, the tank is often equipped with a degassing valve (similar to the one found on a bag of freshly roasted coffee), allowing oxygen to escape while maintaining pressure.
This creates an extremely stable, oxygen-free environment — and the key difference here is control.
What happens inside a carbonic maceration tank?
With no oxygen present and plenty of sugar available from the intact cherry, fermentation occurs primarily inside the fruit itself. This intracellular pathway often emphasises clarity and brightness over raw intensity.
As with other anaerobic methods, organic acids (including lactic acid) can form — but the flavour development is frequently more focused and refined.
How carbonic maceration affects the cup
Carbonic maceration coffees often share similarities with other anaerobic coffees — elevated sweetness, tropical fruit character, and high aromatic intensity. Where they tend to differ is structure and cleanliness.
- Brighter, cleaner fruit expression
- Less overt booziness
- A lively, sometimes fizzy mouthfeel
It’s not uncommon to find flavour associations reminiscent of sparkling wine, sour candy, or champagne — especially when the process is well executed.
Anaerobic vs carbonic maceration: a quick summary
Both methods are anaerobic, but they’re not interchangeable.
- Anaerobic fermentation is a broad category with outcomes that vary widely depending on control and variables.
- Carbonic maceration is a more specific, tightly controlled anaerobic method using CO₂ and whole cherries.
In the cup, anaerobic coffees can range from clean and tropical to deeply funky and winey, while carbonic maceration often lands on the cleaner, brighter end of that spectrum.
Processing should enhance the coffee — not replace it. The best anaerobic and CM coffees still taste like the origin, just with an added layer of sweetness, texture, and aroma.
How to brew anaerobic coffees
Filter and espresso adjustments that work
Many of the same principles that apply to brewing natural coffees also apply to anaerobic and carbonic maceration coffees. Because fermentation makes the beans extract more easily, these coffees often behave differently than washed coffees in the brewer.
Key brewing considerations:
- Anaerobic coffees often benefit from a slightly finer grind, but still tend to run faster than washed coffees due to higher solubility and less fine particles produced when ground.
- Lower brew temperatures — typically around 88–92°C — often help preserve clarity and keep fermentation flavours in balance.
- If the coffee is extremely fermented, consider recipes with fewer pours. This can enhance sweetness and emphasise a more creamy, cohesive mouthfeel.
- Similar to many naturals, anaerobic coffees tend to be forgiving at home — even if your water or equipment isn’t perfectly dialled in.
For espresso, a brew ratio between 2:1 and 2.5:1 is often the sweet spot with anaerobic coffees. Like with pour-over, you can usually expect a slightly faster extraction time to reach balance — very fermented coffees tend to extract smoother, so you don’t need to “push” them as hard to get sweetness.
One of the highest return-on-investment techniques for anaerobic naturals is extract chilling. Using Paragon Espresso can significantly increase perceived sweetness and create a more coating, silky mouthfeel — which matters a lot in espresso, where texture is a huge part of the experience.
The same principle applies to filter brewing. If you want to highlight sweetness and structure while keeping fermented notes clean, Paragon for pour-over is a very effective way to level up the cup.
Final thoughts
Anaerobic fermentation has expanded what coffee can taste like — but it’s not a shortcut to quality. The best results come from producers who understand raw material, fermentation control, and restraint.
When done well, anaerobic and carbonic maceration coffees can offer remarkable sweetness, layered fruit character, and a sense of precision that complements — rather than overwhelms — the coffee’s origin.
Keen to try some anaerobic coffees? See what we have below or explore our full selection.
