Ethanol is
produced as part of a fermentation process in yeast referred to
as anaerobic glycolysis.
Ethanol + NAD+ <=> Acetaldehyde + NADH (catalyzed by Alcohol Dehydrogenase)
See also: Alcoholic
Fermentation, Alcohol Dehydrogenase,
Fermentation, Anaerobic
Glycolysis, see also here