How does fermentation occur?
Fermentation comprises metabolic pathways that maintain electron balance through organic molecules, allowing glycolysis to continue under suitable conditions. Food production uses this biochemical basis. Not every fermentation produces alcohol, and different microorganisms generate different products.
Regenerating electron carriers
Glycolysis requires regeneration of electron acceptors such as NAD+. Lactic acid fermentation reduces pyruvate to lactate, while alcoholic fermentation includes steps producing ethanol and carbon dioxide. The main ATP gain comes from substrate-level phosphorylation during glycolysis. Fermentation should not be confused with anaerobic respiration, which uses an electron transport chain with a nonoxygen terminal acceptor.
Controlled processes in food
Cultures used in yogurt, bread, and vegetable products need different conditions. Temperature, pH, salt, and contamination control influence the result. Gas formation or sourness alone does not establish safety, and spoilage cannot always be distinguished by appearance. Fermentation can alter nutrient composition, but fermented products do not all contain the same living microorganisms or share identical nutritional properties.