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 from winemaking, it's a controlled fermentation associated with some of the most vivid, fruit-forward coffees you'll come across.
In its stricter, wine-derived sense, carbonic maceration means fermenting whole, intact coffee cherries in a sealed tank, with carbon dioxide pumped in to create a low-oxygen environment. Specialty coffee uses the term more loosely, though. Some coffees sold as "washed carbonic maceration" are depulped before the CO2-controlled fermentation, so the label won't always tell you exactly what happened in the tank.
From grape preservation to the World Barista Championship
Carbonic maceration didn't start in coffee, and it didn't even start as a way of making something to drink. In 1934, in Narbonne in southern France, scientist Michel Flanzy was experimenting with storing whole grape clusters in a CO2-rich atmosphere to preserve them. Instead, the intact grapes began fermenting from the inside, driven by their own enzymes rather than by yeast. That work helped establish carbonic maceration as a winemaking technique in its own right.
It found a home in France's Beaujolais region, where carbonic maceration is used to make bright, fruit-forward red wines from Gamay grapes. Whole bunches go into a sealed tank under CO2. The grapes ferment from the inside while yeasts get to work on the juice that collects at the bottom of the tank. The resulting wines are often soft, juicy and approachable young, 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 adapt the approach for a Sudan Rume lot from Finca Las Nubes, using sealed tanks, CO2 and close control of fermentation conditions.
It helped take Šestić to the top of the 2015 World Barista Championship in Seattle. The coffee was described as a washed carbonic maceration: the cherries were depulped before the CO2-controlled fermentation. For his milk course, Šestić blended it 50/50 with a natural-process version of the same lot. His win put carbonic maceration into the specialty coffee conversation, and helped make fermentation something producers use deliberately to shape flavour. You can read more about that lot, and the variety behind it, in our guide to Sudan Rume.
More than a decade on, carbonic maceration has moved well beyond competition coffee and into commercial production around the world.
So, what's actually going on?
The whole-cherry version starts with cherry selection. Producers want ripe, intact fruit for a consistent fermentation. Damaged cherries let unwanted microorganisms in, and underripe ones have less sugar to ferment and can bring green, astringent flavours to the cup. Many producers float the cherries first to remove low-density fruit before anything goes near the tank.
The selected cherries go into a sealed tank, often stainless steel, and carbon dioxide is pumped in to push the oxygen out. How well that works depends on the tank and how closely the process is managed. CO2 on its own won't clear every pocket of oxygen.
That added CO2 is one of the things that sets carbonic maceration apart from other forms of anaerobic fermentation. It's still a type of anaerobic fermentation, though. "Anaerobic" describes the oxygen conditions during fermentation rather than one fixed recipe: coffee can be fermented as whole cherries or after depulping, with or without water, and producers keep oxygen out in different ways. Carbonic maceration, in the strict sense, is the whole-cherry version in a sealed, CO2-rich tank.
No practical fermentation setup is completely sterile. A low-oxygen environment doesn't exclude microorganisms, and CO2 doesn't remove the role they play