Process that allows respiration to occur in the absence of oxygen.
Biologically, it allows cells to obtain energy from molecules (e.g., glucose) anaerobically. Glycolysis, the breakdown of glucose, is a form of fermentation. Alcoholic fermentation occurs when yeast cells convert carbohydrate sources to ethanol and carbon dioxide. Fermentation reactions are common in muscle cells, yeasts, some bacteria, and plants. See also beer ; wine .