The foam, or troth (top yeast), or the sediment (bottom yeast), of beer or other in fermentation, which contains the yeast plant or its spores, and under certain conditions produces fermentation in saccharine or farinaceous substances; a preparation used for raising dough for bread or cakes, and making it light and puffy; barm; ferment.
- Any of various unicellular fungi of the genus Saccharomyces, especially S. cerevisiae, reproducing by budding and from ascospores and capable of fermenting carbohydrates.
- Any of various similar fungi.
- Froth consisting of yeast cells together with the carbon dioxide they produce in the process of fermentation, present in or added to fruit juices and other substances in the production of alcoholic beverages.
- A powdered or compressed commercial preparation, having yeast cells and inert material such as meal and used chiefly as a leavening agent or as a dietary supplement.
- Foam; froth.
- An agent of ferment or activity: political agitators who are the yeast of revolution.
- To ferment.
- To froth or foam.