Yeast. Yeast is either the froth or the deposit of fermenting worts, according to the character of the fermentation. According to Liebig, yeast is a substance in a state of putrefaction or fermentation, the atoms of which are in a continual motion, and this condition it communicates by contact, to fermentable substances. Ludersdorff considers yeast an organic body, acting on the sugar contained in the saccharine solution, and not by mere contact and communication of its own condition. This view receives considerable support by examination of its particles by a microscope, and also from its fermenting power being destroyed by trituration or strong pressure. Cooley believes both views to a certain extent correct, and that the atoms in a state of continual motion or change, referred to by Liebig, are developed by the organs of vital yeast, when in contact with sugar under circumstances favorable to fermentation.

1808. Preparation of Brewers' Yeast

1808.    Preparation of Brewers' Yeast. To do this, 72 pounds unkilned malt and a handful of hops are gradually stirred in a clean tub containing 7 gallons water of 170° Fahr.; and to this 51/2 gallons water of 200° are added. The tub is then covered tightly and left quiet for 1 hour. Supposing this to be done at 6 P. M., the whole is left undisturbed till 7 o'clock next morning, when it must be cooled rapidly, which is done by setting in cans filled with cold water. When the temperature of the mash has reached 70°, the tub is covered again and left during the day till 6 P. M.; at this time 11/2 gallons fresh beer yeast are to be stirred in. In 12 hours pierce a hole in the layer formed by the husks of the malt, and dip 31/2 gallons of the liquor beneath, then stir the whole up and dip 13/4 gallons from it (husks and liquor). This is the mother-barm, from which you can generate yeast all the year round in using it in the way described instead of the ordinary beer leaven. To the remainder in the tub add 5 gallons wort of 90° (see No. 858 (Mashing)), and make use of it in within 2 hours. The mother-yeast also must be used the same day for fermenting another portion.

1809. Yeast for Hot Climates

1809.    Yeast for Hot Climates. Boil 2 ounces of the best hops in 4 quarts water for 1/2 hour; strain it, and let the liquor cool down to new milk warmth. Then put in a small handful of salt and 1/2 pound brown sugar; beat up 1 pound best flour with some of the liquor, and mix all well together. The third day add 3 pounds potatoes boiled and mashed, and let it stand until the next day. Then strain, and it is ready for use. Stir frequently while making, and keep near a fire. Before using, stir well; it will keep 2 or 3 months in a cool place. This yeast is very strong; half the usual quantity necessary for a baking is sufficient. This yeast may be kept in a temperature as high as 104° Fahr.

1810. To Prepare Yeast without a Ferment

1810.    To Prepare Yeast without a Ferment. Common wheat flour is to be mixed with water into a thick paste, and kept, slightly covered, in a moderately warm place, for some time. About the third day it begins to emit a little gas, and to exhale a disagreeable, sour odor, like stale milk ; after the lapse of a few days, that is, about the sixth or seventh day, the smell changes, much gas is evolved, accompanied by a distinct and agreeable vinous odor, and it is then in a state to excite the vinous fermentation. A quantity of wort is next to be prepared, and boiled with hops, in the same manner as in the brewing of beer (see No. 858 (Mashing)), and when cooled to 90° or 100° Fahr., the decomposed dough, thoroughly mixed with tepid water, is to be added, and the whole kept in a warm situation. After the lapse of a few hours, active fermentation takes place, carbonic acid is disengaged, and when the action is complete, and the liquor clear, a large quantity of yeast, of excellent quality, is found at the bottom of the vessel.