The principal forms in which starch comes upon our tables are meals and flours, and the various breads, cakes, mushes, and puddings made out of these.

Far the most valuable and important of all is wheat flour, because this grain contains, as we have seen, not only starch, but a considerable amount of vegetable "meat," or gluten, which is easily digested in the stomach.
This gluten, however, carries with it one disadvantage--its stickiness, or gumminess.

The dough or paste made by mixing wheat flour with water is heavy and wet, or, as we say, "soggy," as compared with that made by mixing oatmeal or corn meal or rice flour with water.

If it is baked in this form, it makes a well-flavored, but rather tough, leathery sort of crust; so those races that use no _leavening_, or rising-stuff, in their wheat bread, roll it out into very thin sheets and bake it on griddles or hot stones.
Most races that have wheat, however, have hit upon a plan for overcoming this heaviness and sogginess, and that is the rather ingenious one of mixing some substance in the dough which will give off bubbles of a gas, _carbon dioxid_, and cause it to puff up and become spongy and light, or, as we say, "full of air." This is what gives bread its well-known spongy or porous texture; but the tiny cells and holes in it are filled, not with air, but with carbon dioxid gas.
Making Bread with Yeast.

There are several ways of lightening bread with carbon dioxid gas.