What does yeast mean?
Yeast most often denotes a single-celled fungus that converts sugars into alcohol and carbon dioxide. In baking, the carbon dioxide expands the dough, while in brewing and winemaking, yeast transforms fermented sugars into alcohol. The word can also refer to a preparation or culture of these organisms, particularly baker's yeast. Figuratively, yeast can describe a process of rapid growth, development, or widespread influence. As a verb, yeast means to ferment and, in more literary or figurative contexts, to spread or multiply rapidly. Although commonly associated with bread and beer, yeast belongs to the fungi rather than to bacteria, and its scientific study has made it an important model for cell biology and genetics. The word's history also reflects its everyday importance: it descends from an Old English term associated with foam and froth, linking the modern organism to the bubbles produced during fermentation.
A single-celled fungus that ferments sugars, especially the kind used in bread, beer, and wine; also, a preparation or culture of such fungi.
"A spoonful of yeast can leaven a whole batch of bread dough."
Usually a mass noun when referring to baker's or brewer's yeast.
To ferment or cause something to ferment; figuratively, to multiply, develop, or spread rapidly.
"Wild yeast slowly fermented the grape juice over several days."
The verb is relatively uncommon; figurative uses often describe rumors, unrest, or other developments that rapidly spread.
The noun is usually uncountable when referring to yeast as a substance or mass. The plural is used when distinct strains, species, or cultures are meant.
"The laboratory maintains a collection of yeasts collected from wine and beer."
The word's ancestor meant foam or froth, so yeast was named for the bubbles it creates.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does yeast come from?
The English noun descends from Old English gist, meaning “foam” or “froth,” through Middle English. It is cognate with Old Norse gis, Middle Dutch gest, and German Gist, reflecting a Germanic vocabulary associated with foam and fermentation.
Related word forms
How yeast is actually used
The noun and verb are standard in British and American English, although the verb is much less common than the noun. The noun is generally treated as a mass noun, while the plural occurs when different strains, species, or cultures are being discussed.