Yeast is a minute form of plant life and when introduced into any substance which is rich in sugar, starch, or gluten, and exposed to air, warmth, and moisture, causes fermenta- tion, which produces new compounds. There are several kinds of fermentation, — lactic fermen- tation, which causes milk to sour; alcoholic fermentation, which is illustrated by the changes juices undergo in the making of wine, cider, and beer ; acetic fermentation, which is caused by too prolonged alcoholic fermentation, as in making vinegar from cider. Alcoholic fermentation produces carbon dioxide gas, which has no unpleasant taste and is, therefore, the kind of fermen- tation best suited for bread-making, the object being not to produce alcohol, but to puff up the dough and make the bread light. Wheat flour contains starch and gluten, and a ferment called diastase, and if moistened and kept warm it would change in time or ferment ; but when this change takes place slowly the dough will be sour. This change may be hastened by the addition of yeast. Yeast, in its natural state, when viewed under the micro- scope, is found to be a plant of the fungus tribe, of which mould and mildew are familiar forms. It is one of the simplest and smallest forms of vegetable life, and is made up of cells which contain liquid or sap. These cells are found in fruit juices and sprouting grains, and they expand rapidly when exposed to air and moisture, and start the decomposition of the sugar in the grain or fruit. To make yeast, grains which contain starch and gluten are moistened and left for the yeast cells to grow. Fermen- tation is checked after a time and the product is prepared ii) various ways for keeping and sold under the forms of dry, liquid, and compressed yeast. The life of the yeast cells is not destroyed and they will BREAD 257 grow again when exposed to warmth and moisture, and suppHed with food ; the same as other forms of vegetable life, after being kept for a time, will grow when planted in proper soil. The temperature of boiling water will kill the yeast plant, and so in using yeast, it is necessary to have the proper temperature. In making bread, put the yeast into the flour ; moisten it ; keep it warm, and thus provide the food and conditions necessary to waken the yeast plant into life again. The yeast cells begin to grow in the dough, thus causing a change in the flour. The diastase ferments and causes some of the starch to change into a kind of sugar, and the sugar changes into carbon dioxide gas and alcohol. In converting the starch into sugar in the dough, there is no change evident to the eye ; but as soon as the sugar is changed to carbon dioxide gas and alcohol, large bubbles of gas appear. The gas, being lighter than the dough, rises, and in its efforts to escape, puffs up the gluten, and as the gluten is elastic it can stretch to several times its original bulk. It is on account of this peculiar tenacity or power of the wheat gluten to hold the gas that wheat flour makes the lightest bread. The gas fills the dough with minute air cells, which — should the yeast have been mixed uniformly with the flour — make it light and spongy.

AI-modernized reading of the original text

Yeast is a minute form of plant life and when introduced into any substance which is rich in sugar, starch, or gluten, and exposed to air, warmth, and moisture, causes fermentation, which produces new compounds. There are several kinds of fermentation, — lactic fermentation, which causes milk to sour; alcoholic fermentation, which is illustrated by the changes juices undergo in the making of wine, cider, and beer ; acetic fermentation, which is caused by too prolonged alcoholic fermentation, as in making vinegar from cider. Alcoholic fermentation produces carbon dioxide gas, which has no unpleasant taste and is, therefore, the kind of fermentation best suited for bread-making, the object being not to produce alcohol, but to puff up the dough and make the bread light. Wheat flour contains starch and gluten, and a ferment called diastase, and if moistened and kept warm it would change in time or ferment ; but when this change takes place slowly the dough will be sour. This change may be hastened by the addition of yeast. Yeast, in its natural state, when viewed under the microscope, is found to be a plant of the fungus tribe, of which mould and mildew are familiar forms. It is one of the simplest and smallest forms of vegetable life, and is made up of cells which contain liquid or sap. These cells are found in fruit juices and sprouting grains, and they expand rapidly when exposed to air and moisture, and start the decomposition of the sugar in the grain or fruit. To make yeast, grains which contain starch and gluten are moistened and left for the yeast cells to grow. Fermentation is checked after a time and the product is prepared ii) various ways for keeping and sold under the forms of dry, liquid, and compressed yeast. The life of the yeast cells is not destroyed and they will BREAD 257 grow again when exposed to warmth and moisture, and suppHed with food ; the same as other forms of vegetable life, after being kept for a time, will grow when planted in proper soil. The temperature of boiling water will kill the yeast plant, and so in using yeast, it is necessary to have the proper temperature. In making bread, put the yeast into the flour ; moisten it ; keep it warm, and thus provide the food and conditions necessary to waken the yeast plant into life again. The yeast cells begin to grow in the dough, thus causing a change in the flour. The diastase ferments and causes some of the starch to change into a kind of sugar, and the sugar changes into carbon dioxide gas and alcohol. In converting the starch into sugar in the dough, there is no change evident to the eye ; but as soon as the sugar is changed to carbon dioxide gas and alcohol, large bubbles of gas appear. The gas, being lighter than the dough, rises, and in its efforts to escape, puffs up the gluten, and as the gluten is elastic it can stretch to several times its original bulk. It is on account of this peculiar tenacity or power of the wheat gluten to hold the gas that wheat flour makes the lightest bread. The gas fills the dough with minute air cells, which — should the yeast have been mixed uniformly with the flour — make it light and spongy.

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