If flour be mixed with sufficient water, the particles will cohere and form a smooth elastic substance called dough. When a little yeast is added to the flour before, or as it is being mixed with the water, and the dough is placed for an hour or two near the fire, the warmth will cause the yeast to make it ferment, or rise, as cooks say - that is, it will swell up. This fermentation is the consequence of the peculiar action which yeast exercises over moist flour. It first changes a part of the starch which is in the flour into sugar, and then turns this sugar into alcohol and carbonic acid, in exactly the same way as it does in the worts of the brewer or spirit distiller. Therefore, when the poorer classes objected to unfermented bread as being "without its gin," they were scientifically correct, although the greater part of the alcohol escapes during the baking of the loaf, and is actually lost in the oven. The carbonic acid gas, unable to make its way out through the glutinous dough, forms large bubbles within it and makes it swell, till the heat of the oven at last kills the yeast plant, when the fermentation suddenly ceases ; this takes place when the heat reaches the boiling-point - 2120; till then heat assists the fermentation.

New bread is very soft and pleasant, though from its spongy nature it is thought indigestible. In a day or two it becomes stale and will crumble. It can be made as fresh as ever again, however, by just dipping it in water and exposing it again to the heat of an oven, or treating it in a closely covered tin. The same effect is produced without wetting the bread, if the heat to which it is subjected is at 2120.

The bread we eat is nearly one-half water, for the flour contains water naturally, and absorbs much more in its conversion into bread. One hundred pounds of wheaten flour take up fifty pounds weight of water, and yield one hundred and fifty pounds of bread. The water does not evaporate from the bread in the oven and the air, as much as we might expect, because the gluten, or flour, is difficult to dry, and retains the water; part of the starch is converted into gum, and also holds it, and the crust of the loaf, which is dry and thick, retains the moisture within it. Wheaten bread contains in due proportions - water, gluten, starch, sugar, and gum.

By making bread at home we save the weight of water used in making each loaf, a very considerable economy in a large family.