What is the process by which yeast converts sugar to alcohol called?

The process by which yeast converts sugar to alcohol is called alcoholic fermentation, or ethanol fermentation. In this anaerobic process, yeast breaks down sugars such as glucose and produces ethanol and carbon dioxide. The carbon dioxide makes bread dough rise, while the ethanol is central to producing beer, wine, cider, and other fermented drinks.

The process begins with glycolysis, which converts glucose into pyruvate and produces a small amount of usable energy. Yeast then converts pyruvate into acetaldehyde, releasing carbon dioxide. Alcohol dehydrogenase finally converts acetaldehyde into ethanol while regenerating NAD+, a molecule needed for glycolysis to continue.

One glucose molecule yields two molecules each of ethanol and carbon dioxide, along with a net gain of two ATP molecules. Fermentation is often associated with a lack of oxygen, although some yeasts can ferment even when oxygen is present if conditions favor it. This distinguishes alcoholic fermentation from lactic acid fermentation, which produces lactate rather than ethanol. The process is not photosynthesis, and it is different from complete cellular respiration, which produces carbon dioxide and water without alcohol as the main end product.