Fermentation
also: coffee fermentation
Microbial breakdown of the sugary mucilage and fruit that develops flavor in green coffee, or ruins it if uncontrolled.
Fermentation is the stage where microbes (yeasts and bacteria) feed on the sugars in coffee’s fruit and mucilage, the sticky layer wrapping each seed. As they eat, they produce acids, alcohols, and aromatic compounds that soak into the bean and shape how it eventually tastes.
Every processing method involves some fermentation. In washed coffee, beans sit in tanks (often 12 to 48 hours) until the mucilage breaks down enough to rinse off. In natural process, the whole cherry ferments slowly as it dries. Anaerobic and carbonic methods seal the fruit in oxygen-limited tanks to steer which microbes dominate.
Why it matters: fermentation is one of the biggest flavor levers a producer controls. Done well, it builds clean sweetness, bright acidity, and complexity. Pushed too far or left to wild microbes, it tips into sour, boozy, oniony, or vinegary off-notes that show up clearly in the cup. Time, temperature, and pH are watched closely.