The economy of food ; a popular treatise on nutrition, food and diet / by J. Alan Murray.

  • Murray, J. Alan (John Alan)
Date:
1911
Catalogue details

Licence: In copyright

Credit: The economy of food ; a popular treatise on nutrition, food and diet / by J. Alan Murray. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    into alcohol and carbonic acid gas ; the process is called alcohohc fermentation. The yeast floats on the surface of the liquor ; it can be skimmed off when its work is done, and used over again. The quantity of yeast increases each time it is used in this way, and the brewers are usually glad to seU some of it. The action of yeast in bread making is of a similar kind. The j^-east is mixed with the dough, and allowed to stand at a suitable temperature. Fermentation sets in and carbonic acid gas is pro- duced. The tiny bubbles of gas, which remain entangled in the dough, expand greatly on the apphcation of heat and cause the bread to “ rise.” If the fermentation be too long continued, or if the yeast be not pure, lactic acid may be formed, and the bread will be sour. The activity of the yeast is destroyed, and the process arrested, by the high temperature to which it is exposed when the bread is baked. To facilitate distribution, yeast is put up in packets in the dry form. The yeast, after being separated from impurities and washed with water, is mixed with starch. A stiff dough is thus formed which can be moulded into cakes and dried at a low temperature. Sometimes the starch is dis- pensed with, the pure yeast being simply moulded into cakes by pressure. If kept in a cool place, these dry yeasts remain fresh and active for a long time. The action of baking powders, which are some- times used instead of yeast to “ raise ” bread and cakes, also depends upon the formation of carbonic acid gas. In this case, however, the gas is formed, not by the action of the powder on the carbohy-