Which compound is a byproduct of alcoholic fermentation?

During alcoholic fermentation, sugars are converted into ethanol and carbon dioxide. This process occurs in yeast and some types of bacteria when oxygen is not available. The primary aim of fermentation is to regenerate NAD+ from NADH, which is essential for allowing glycolysis to continue producing ATP in the absence of oxygen.

Carbon dioxide is released as a byproduct of the decarboxylation that takes place when pyruvate is converted to acetaldehyde, which subsequently gets reduced to ethanol. This release of carbon dioxide is what contributes to the bubbling or fizzing that can be observed in fermentation processes, such as the fermentation of beverages like beer and wine.

Other options do not align with the byproducts of alcoholic fermentation: oxygen is involved in aerobic respiration, water is generally a product of cellular respiration but not directly from fermentation, and lactate is produced in lactic acid fermentation, which is distinct from alcoholic fermentation. Therefore, the correct answer points directly to carbon dioxide as a byproduct of the fermentation process.