Fermentation

Fermentation is the transformation of food by microorganisms — yeasts, bacteria, and molds. It is one of the oldest and most consequential food technologies: bread, cheese, yogurt, wine, beer, soy sauce, vinegar, chocolate, coffee, and kimchi are all fermented foods. In every case, microbes do work that humans cannot — breaking down complex molecules into simpler, more flavorful, more digestible, or more preserved forms.

The basic mechanism

Fermentation in the strict biochemical sense is anaerobic metabolism — organisms extracting energy from sugars without oxygen, producing alcohol or organic acids as byproducts. In culinary use, the term is broader, encompassing any microbial transformation of food.