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n. The foam, or troth or the sediment 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. Spume, or foam, of water. Yeast cake, a mealy cake impregnated with the live germs of the yeast plant, and used as a conveniently transportable substitute for yeast.

 - Yeast plant (Bot.), the vegetable organism, or fungus, of which beer yeast consists. The yeast plant is composed of simple cells, ...