yeast (yest)

[Formerly also yest; also dial. east; ζεστός, boiled, boiling); Skt. ✔ yas, boil, froth.] 1. A yellowish substance, having an acid reaction, produced during the alcoholic fermentation of saccharine fluids, rising partly to the surface in the form of a frothy, flocculent, viscid matter ( top or surface yeast ), and partly falling to the bottom ( bottom or sediment yeast ). Yeast consists of aggregations of minute cells, each cell constituting a distinct plant, Saccharomyces cerevisiæ. The yeast-plant is a saprophytic fungus of uncertain systematic position, being regarded by some as a degenerate ascomycete, by others as representing a distinct cla . It exists under two conditions. In the first it is in the form of transparent round or oval cells, averaging.08 mm. (.003 inch) in diameter, which increase in countle numbers by budding - that is, by the formation of small daughter cell by the side of the mother-cell, from which it sooner or later separates. The other form consists of larger cells, which, by a division of their protoplasm, form four new cells within the parent-cell. These endogenously formed cells have been likened to the ascospores of the Ascomycetes, IMG:content-2679.png:[blocks in formation] a, yeast-plant ( Saccharomyces cere visia ), showing increase by budding; b, a cell, showing the formation of the spores; c, a cell, containing four mature spores; d, the spores; e, germinating spores. with which, as stated above, they are frequently cla ed. The former notion that the yeast-plant was only the im by Brefeld's elaborate researches. Fermentation takes She consented that the village maiden should manufacture yeast , both liquid and in cakes. Hawthorne, Seven Gables, v. 2. Spume or foam of water; froth. Now the ship boring the moon with her mainmast, and anon swallowed with yest and froth. Shak., W. T., iii. 3. 94. They melt into thy yeast of waves, which mar Alike the Armada's pride, or spoils of Trafalgar. Byron, Childe Harold, iv. 181. Artificial yeast, a dough of flour and a small quantity of common yeast, made into small cakes and dried. Kept free from moisture, it long retains its fermentative property.- Beer-yeast, the common yeast, Saccharomyces cerevisiæ, which is added to the wort of beer for the purpose of exciting fermentation. See def. 1.-Bottom or sediment yeast. See def. 1.-German yeast, com mon yeast collected, pre ed till nearly dry. 7014