We mammals start with oxygen and glucose and end, essentially, with the waste products carbon dioxide and lactic acid. It’s the same stuff that spoilage bacteria make, and the same stuff in pickles. But yeasts end up not with lactic acid but with another molecule, acetaldehyde. And they don’t stop there. Yeasts string hydrogen atoms onto that, making ethanol and ATP, and then the ethanol diffuses into the environment. Yay! We have made booze.
