When yeast cells ferment glucose anaerobically, pyruvate is converted to ethanol in a two-step sequence. Which compound is the intermediate released by the first step?

Core Concept

Alcoholic fermentation first deploys pyruvate decarboxylase, which removes CO2 from pyruvate and releases the two-carbon compound acetaldehyde. Alcohol dehydrogenase then reduces acetaldehyde to ethanol while oxidizing NADH back to NAD+. That second step matters most metabolically because refilling the NAD+ pool lets glycolysis continue making ATP without oxygen.