Fermentation is a chemical process where microorganisms like yeast or bacteria break down sugars and starches, creating new substances. When yeast ferments grape juice, it produces wine. When bacteria ferment milk, they create yogurt or cheese. Humans have used fermentation for thousands of years to preserve food and create new flavors.

As a noun, ferment also describes a state of excitement, unrest, or change. When a classroom is in ferment over an upcoming field trip, students are buzzing with anticipation and energy. During the American Revolution, the colonies were in political ferment, with ideas about independence spreading and changing rapidly.