YEAST, an insoluble substance forming an essential component of all sacchariferous juices when in the state of vinous fermentation. This subject is pretty fully dealt with under Fermentation (see vol. ix. pp. 92, 95, 97); one important application of yeast, however, viz., that which it finds in the baker’s trade, is there only referred to. To produce a spongy loaf, the dough, before being made into loaves, is mixed with a ferment which, if allowed to act for a sufficient time before baking, produces alcohol and carbonic acid from a small portion of the actual or potential sugar present; and the carbonic acid, being liberated from within the dough, causes it to “rise.” In former times leaven (see Baking, vol. iii. p. 253) used to be employed exclusively. For higher classes of bakery yeast is now preferred. The yeast produced so abundantly in beer-brewing is available; but its bitter taste is an objection to it. Hence it has long been customary in Germany to produce yeast expressly for bakers’ and cooks’ purposes, which may, of course, be done in a variety of ways. A method frequently used is to produce a wort (see Brewing, vol. iv. p. 275) from barley, malt, and rye, and by the addition of a little ready-made yeast to let it ferment under conditions which favour the growth of yeast-cells, but restrict the proportion of alcohol produced to a minimum (comp. Fermentation, vol. ix. p. 97). During the most tumultuous period of the process the yeast is skimmed off from the surface, washed with water, and either “filter-pressed” or “centrifuged” to obtain it as a relatively dry paste; it is then mixed with a proportion of dry starch, to give it a higher degree of dryness. Such yeast goes into commerce as presshefe or pfundhefe (German yeast or barm). This ...