Carbonic maceration is one of those terms that makes coffee sound like it's wandered in from a wine bar. Which, to be fair, it has. Borrowed straight from winemaking, this processing method is behind some of the most vivid, fruit-packed coffees you'll come across.
At its core, carbonic maceration is about fermenting whole, intact coffee cherries in a sealed tank that's been flushed with carbon dioxide. That low-oxygen setup nudges the fruit into a different kind of fermentation, one that happens inside the cherry itself before any microbes get going on the outside. The result is a coffee with striking clarity, layered sweetness, and flavours that feel dialled up rather than muddled.
From grape preservation to the winner's circle
Carbonic maceration didn't start in coffee, and it didn't even start as a way of making something to drink. It was first explored in the 1930s by French scientist Michel Flanzy, who stored whole grape clusters in a low-oxygen, CO2-rich atmosphere as a method of preserving fruit. What he found was that the intact grapes began to ferment from the inside, without any added yeast. That discovery went on to become a winemaking technique in its own right.
It found its spiritual home in France's Beaujolais region, where it's used to make bright, fruit-forward red wines from Gamay grapes. Whole bunches go into a sealed tank, CO2 fills the space, and fermentation begins inside the grapes before yeast gets involved on the outside. The result is wine that's soft, juicy, and ready to drink early, with Beaujolais Nouveau the best-known example.
The jump to coffee came via Saša Šestić, the Bosnian-Australian barista and founder of Ona Coffee. After spending time with Australian winemaker Tim Kirk of Clonakilla, Šestić worked with Colombian producer Camilo Merizalde to apply the same thinking to a Sudan Rume lot from Finca Las Nubes: sealed tanks, CO2, temperature control, the works.
It took him to the top of the 2015 World Barista Championship in Seattle. He served the coffee as a washed carbonic maceration, blended in his milk course with a more conventionally processed version of the same lot, and the cup stood out immediately. Clean but punchy. Fruit-forward but precise. His win played a major role in bringing carbonic maceration into mainstream specialty conversation, and in a broader shift in how producers think about fermentation, not just as a step, but as a tool. You can read more about that lot, and the variety behind it, in our guide to Sudan Rume.
A decade on, carbonic maceration has moved well beyond competition coffee and into commercial production around the world.
So, what's actually going on?
It starts with cherry selection. Only ripe, intact fruit makes the cut. Damaged or underripe cherries would let external microorganisms in too early and undermine the whole point of the method. Many producers float the cherries first to remove low-density "floaters" before anything goes near the tank.
Those selected cherries go into a sealed tank, typically stainless steel, which is then flushed with carbon dioxide from an external source. Because CO2 is heavier than air, it physically displaces much of the oxygen, creating a largely oxygen-free environment from the outset.
This is one of the key differences between carbonic maceration and standard anaerobic fermentation. Most producers doing anaerobic fermentation start by immersing depulped coffee in water and rely on native yeasts and bacteria to consume the initial oxygen before anaerobic metabolism takes over. In carbonic maceration, the oxygen-free environment is created chemically at the start; in most anaerobic fermentation, it's created microbiologically as the process unfolds.
It's worth saying that complete sterility isn't really achievable in either case, it's a question of dominance rather than total exclusion. But the CO2 flush gives carbonic maceration producers an earlier, more stable starting point.
Here's where it gets interesting. With little oxygen present and the cherry skins still intact, external microbes have limited access to the sugars inside the fruit. Instead, the fruit's own cells switch to anaerobic metabolism. Enzymes within the cell drive glycolysis, breaking sugars down into ethanol and CO2, degrading malic acid, and generating a range of higher alcohols and aromatic precursors along the way. Ethanol levels stay low, usually no more than around 2%, but the aromatic groundwork laid here is what gives these coffees their signature. This is intracellular fermentation, and it continues until the cherry skins eventually break down, at which point more conventional microbial fermentation takes over on the outside.
Throughout, producers can monitor and adjust temperature, CO2 levels, pH, and fermentation duration. Tanks are often held around 30 to 32°C to keep those enzymes active, though some producers drop to 18 to 22°C for a subtler, more delicate profile, and maceration commonly runs anywhere from five to ten days. That level of control is what sets carbonic maceration apart from open-air fermentation, where the environment is at the mercy of weather, ambient temperature, and whatever microflora happen to be in the vicinity.
There's also a related technique worth knowing about, often called anoxic fermentation, where producers take the CO2-flush approach further by pitching a specific lab-cultivated yeast culture into the tank. It shares the starting premise with carbonic maceration (remove oxygen chemically rather than microbiologically) but takes the control question in a different direction, selecting the microbes that do the fermenting rather than leaving it to the cherry's own enzymes. Our deep dive on anaerobic fermentation covers this in more detail.
Whole cherry, or not? A note on the term
Strictly speaking, true carbonic maceration requires whole, intact, unpulped cherries. That's what separates it from the broader family of anaerobic fermentation, where the coffee might be depulped before it ever reaches the tank. The intact skin is the whole point: it's what keeps the fermentation intracellular for as long as possible.
In practice, though, the label gets used loosely. Plenty of coffees sold as "carbonic maceration" are pulped at some stage, and producers vary their techniques enormously, so the term covers more ground than its winemaking origins suggest. Even the lot that arguably launched the method in specialty, Šestić's 2015 Sudan Rume, was a washed carbonic maceration, which means the fruit was removed at some point in the process.
None of this makes those coffees any lesser. It just means "carbonic maceration" on a bag tells you about the intent and the broad approach rather than guaranteeing a textbook whole-cherry ferment. When in doubt, it's always worth asking the roaster what actually happened in the tank.
How does it compare to other processing methods?
Washed coffees are all about clarity. The fruit is removed early, leaving the bean to show clean acidity and structure. Processing stays out of the way, letting terroir and variety speak.
Natural coffees go the other way. The whole cherry dries around the seed over days or weeks, building body and fruitiness, sometimes beautifully, sometimes unpredictably, depending on how carefully conditions are managed.
Honey processing sits in the middle. Some mucilage is left on the seed during drying, adding sweetness and texture without going full natural.
Carbonic maceration plays a different game. It's not just about what's left on the bean during drying, but how the fruit behaves before it's removed. The sealed, controlled environment lets producers shape flavour in a much more deliberate way than any of the methods above allow.
It's worth remembering that carbonic maceration is a fermentation step, not a complete processing method on its own. Once the tank stage is finished, the coffee still needs to be dried, and that drying can follow washed, honey, or natural principles. Each combination pulls the cup in a different direction, which is part of why two carbonic maceration coffees can taste so unlike one another.
What does it taste like?
In a word: expressive.
Expect red fruits like cherry, raspberry, and plum, often backed by tropical notes such as mango, lychee, and passionfruit. There's usually a rounded, almost silky mouthfeel, with acidity that's bright but well behaved, sometimes with a soft, lactic edge. The finish tends to be aromatic and lingering, with layers that reveal themselves as the cup cools.
A lot of that character comes from esters, the aromatic compounds formed when alcohols produced during fermentation react with organic acids in the fruit. The extended intracellular phase tends to produce them in abundance, and carbonic maceration in particular is associated with higher levels of cinnamate esters. That's part of why these coffees can read as more aromatic and lifted than a sealed-tank anaerobic from the same farm. It isn't simply more fermentation, it's a different set of compounds.
One myth worth busting: despite the wine-bar associations, these coffees aren't boozy. The small amount of ethanol made in the tank almost entirely evaporates during drying and roasting, so a brewed cup carries only a trace, roughly on a par with a very ripe banana. What survives is the aroma, not the alcohol.
Compared to some anaerobic coffees, which can lean heavier or more intensely fermented, carbonic maceration often feels more focused. Still bold, but cleaner around the edges. It's no coincidence these coffees show up in barista competitions. They reward careful brewing, and filter methods like the V60 or Chemex tend to let the aromatics shine.
A note for home roasters
If you roast your own coffee, carbonic maceration lots benefit from a lighter touch. The fermentation process can affect the bean's physical structure, often resulting in higher sugar content and greater heat sensitivity.
You'll often find a delayed first crack compared to conventionally processed coffees from the same origin, and the window between development and scorching can be narrower than you'd expect. Slower heat application and careful monitoring through first crack tend to pay off. The flavour compounds you're trying to preserve are delicate, and they don't respond well to being rushed.
Give it a try
The easiest way to get your head around carbonic maceration is to taste it. We stock coffees processed this way when available, alongside other fermentation-led lots. Have a look at what's on right now.
If you'd like to go deeper on the broader family of oxygen-free fermentation methods, our deep dive on anaerobic fermentation is a good next step. Same family, different personality.