Controlled Rot

Fermentation is what happens when microorganisms — usually yeast or bacteria — break down sugars in the absence of oxygen. The byproducts depend on which microbe is doing the work.

Humans stumbled onto fermentation at least 9,000 years ago. The oldest known fermented beverage comes from Jiahu, China — a rice-honey-fruit wine dated to 7000 BCE. Nobody understood the chemistry. They just noticed that leaving fruit juice in a warm place made it bubbly and intoxicating.