Wheat flour is the important material in this group, but muffins and biscuit may be varied by the use of corn meal, rye, and Graham flour, and cooked cereals may also be utilized. The ingredients are flour, salt, a liquid, sometimes a fat, eggs, and sugar. The flavorings are spices, essences, fruit juice, dried fruits, nuts, chocolate. The mixture must be smooth, but it is also necessary to make it porous or "light." This is accomplished by means of leavening agents, "to leaven "meaning" to make light."
The batter, or dough, is leavened by introducing into it air or a gas that expands when heated in the oven, thus making the whole more porous and larger in bulk.
This is introduced into the batter by beating, or by beating air into the white of egg and stirring the beaten white into the batter.