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framework of support for the dough, the heat is lessened or withdrawn, the air will escape, or contract to its former volume, allowing the distended glutinous cell walls to collapse; in either case the bread will be heavy. If carbonic acid gas, generated within the dough by means of fermentation or by the use of chemical substances, be the means used to lighten the mass, the gluten by virtue of its tenacity holds the bubbles of gas as they are generated, and prevents the large and small ones from uniting, or from rising to the surface, as they seek to do, being lighter than the dough. Being thus caught where they are generated, and the proper conditions supplied to expand them, they swell or raise the dough, which is then termed a loaf. (This word "loaf" is from the Anglo-Saxon _hlifian_, to raise or lift up.) The structure is rendered permanent by the application of heat in baking. BREAD MADE LIGHT BY FERMENTATION. For general use, the most convenient form of bread is usually considered to be that made from wheat flour, raised or made light by some method of fermentation, although in point of nutritive value and healthfulness, it does not equal light, unfermented, or aerated bread made without the aid of chemicals. THE PROCESS OF FERMENTATION.--Fermentation is a process of decomposition, and hence more or less destructive to the substances subjected to its influence. When animal and vegetable substances containing large amounts of nitrogenous elements are in a moist state and exposed to air, they very soon undergo a change, the result of which is decomposition or decay. This is occasioned by the action of germs, which feed upon nitrogenous substances, as do the various species of fungi. Meat, eggs, milk, and other foods rich in nitrogenous elements can be preserved but a short time if exposed to the atmosphere. The carbonaceous elements are different in this respect. When pure starch, sugar, or fat is exposed to the air in a moistened state, they exhibit the very little tendency to change or decay. Yet if placed in contact with decomposing substances containing nitrogen, they soon begin to change, and are themselves decomposed and destroyed. This communication of the condition of change from one class of substances to another, is termed fermentation. If a fermenting substance be added to a watery solution containing sugar, the sugar will be changed or decomposed, and two new substances, alcohol and carbonic
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