Fermentation is the process in which a substance breaks down into a simpler substance. Microorganisms like yeast and bacteria usually play a role in the fermentation process, creating beer, wine, bread, kimchi, yogurt and other foods.
Fermentation comes from the Latin word fermentare, meaning “to leaven.” To make bread rise, you use a leavening agent to “wake up” dry yeast by mixing it with water. The yeast then starts “eating” the sugar in the dough and off-gassing alcohol: that’s fermentation. Grape juice becomes wine as the fermentation process is complete.