Kiau, Tsiu-kiau, . Cum. Tart, Sandi, Nardi, HIND. Tsiu-rou, Shin-kiuh, „ Spurna di cervogia, . Ir.
Yest FB. Se. . . TAM., TEL.
lie fen, GEB.
Yeast is a product of the fermentation by which beer is made, upon the surface of which it swims from involving bubbles of carbonic acid gas. It may be obtained in the form of a firm paste. Mixed with moistened flour, it excites the panary fermentation, and is thus used, for baking bread. Yeast is a plant belonging to the fungi in the state of sporules or thallus ; or the true aerial tufts or heads of spornles, of a multitude of minute oval or circulating bodies or sporules, endowed, under certain favourable circumstances. with extraordinary powers of growth and multi plication. In Britain, three kinds, viz. brewer's, German, and patent yatst. fire employed in the manufacture of bread. In the E. Indies, the yeast employed is the fermenting juice of the palms, known as toddy. The vitality of dry yeast is destroyed by falls, blows, bruises, or rough mechan ical injuries, as also heat, cold, and chemical reag,ents. The presence of yeast a substance
containing sugar, or starch convertible into sugar and nitrogenized matter, induces certain chemical changes comprehended under the term vinous or alcoholic fermentation. These changes in the making of bread consist in the conversion of sugar of flour into alcohol and carbonic acid gas ; the latter, in its efforts to esc,ape from the dough with which it is mixed, distends it, forming vesicular spaces in its interior, and so causing it to become porous and light. A genus and species have been constituted for the reception of this organism, under the name of Saccharomyces cerevisre. This plant has been supposed to be the active cause of fermentation, and the carbonic acid given off during that process has been re garded as the result of the growth of the plant. In China yeast is used medicinally.—Schleiden, Principles of Scientific Botany ; Micrographic Dictionary ; Snzith; Poole, St. of Commerce.