The most reliable and convenient quick leavening agent is a pure cream of tartar baking-powder. If pure, it will contain only soda bicarbonate and cream of tartar mixed by weight in the correct proportion, and combined with the least possible amount of cornstarch or flour necessary for its perfect keeping. Any amount of starch above this is an adulteration as truly as if some harmful substance were used. Baking-powders having their formula printed on the label of their tins, may be relied upon. Biscuits made without eggs require two level teaspoons of baking-powder for each cup of flour. Muffins and rich cakes with eggs, from one and one-half to one level teaspoon for each cup of flour or meal.
Soda is also neutralized by sour milk or lactic acid. This is economical, particularly for those who have plenty of pure milk. But milk in winter grows bitter before it sours; and the degree of acidity varies so much that the result is often failure. Sour milk is best when it sours quickly, and is thick and smooth, not separated. One even teaspoonful of soda to one pint of nicely thickened or loppered milk is the proportion. When the milk tastes or smells sour, but is not thick, use it as sweet milk in gingerbread or brown bread, where you have molasses to complete the acidity. Add a very little more soda if the receipt call for sweet milk, or a little less if for sour milk.
Nearly all kinds of soda biscuit, muffins, gems, etc., should have the dry ingredients mixed in one bowl, and the liquids, such as milk, eggs, melted butter, etc., in another; and when ready to bake, stir the two quickly and thoroughly together, and bake immediately in a very hot oven.
Molasses gives another acid which is combined with soda, to raise and lighten dough. Directions for its use are given under rules for brown bread and molasses gingerbread.