Fermentation · 9 min read
For most of coffee's commercial history, fermentation was an accident — an unavoidable step in washing coffee cherries that producers tried to control rather than celebrate. But in the last decade, a quiet revolution has swept through coffee-producing countries. Inspired by winemaking and beer brewing, a new generation of producers is treating fermentation as a deliberate flavor tool.
Fermentation in coffee occurs when microorganisms — yeasts and bacteria — break down the sugars in the mucilage surrounding the coffee seed. In traditional washed processing, cherries are depulped and soaked in water tanks for 12 to 72 hours. Natural processing dries the entire cherry intact, allowing prolonged contact between the seed and the fermenting fruit, producing wild, fruity, wine-like flavors.
The real breakthroughs have come from controlled anaerobic fermentation. Pioneered by producers in Colombia, Costa Rica, and Ethiopia, this technique places depulped or whole cherries in sealed, oxygen-free tanks. Without oxygen, different metabolic pathways activate, producing flavor compounds that aerobic fermentation simply cannot. The results can be extraordinary: coffees that taste of passionfruit, cinnamon, strawberry jam, or even bubblegum.
Carbonic maceration, borrowed directly from Beaujolais winemaking, is another technique gaining traction. Whole cherries are sealed in tanks filled with carbon dioxide, forcing intracellular fermentation within the fruit itself. The flavors produced are vivid, complex, and polarizing.
The ethical dimension deserves attention. These experimental processes require significant investment. When they succeed, they can transform a farmer's livelihood. The challenge for the specialty industry is to ensure that fermentation innovation benefits producers equitably.