During fermentation, what does one molecule of glucose break down into?

The breakdown of one molecule of glucose during fermentation ultimately yields two molecules of ethanol and two molecules of carbon dioxide. This process occurs primarily in yeast and is a form of anaerobic respiration.

When glucose, a six-carbon sugar, undergoes fermentation, it is first converted into pyruvate through glycolysis, which produces two molecules of pyruvate, along with a net gain of two ATP molecules and two NADH molecules. Each pyruvate then undergoes decarboxylation, releasing a molecule of carbon dioxide and converting into acetaldehyde. Subsequently, acetaldehyde is reduced to ethanol in a reaction that regenerates NAD+, which is necessary for the continuation of glycolysis.

This means that for every glucose molecule processed through this pathway, the final products are indeed two molecules of ethanol and two molecules of carbon dioxide. This stoichiometric relationship is fundamental in brewing and winemaking, as it defines the alcohol and CO2 content produced during fermentation.