When we are not using sour milk or molasses, we must look elsewhere for an acid to combine with our soda in order to give us the required gas. There are several such acids which when combined with soda form the baking-powders to be had on the market. The best of these is made of soda and cream of tartar mixed with a little starch to keep it from absorbing moisture. Cream of tartar is the salt of an organic acid found in grapes and when combined with soda leaves a salt in the muffin. This salt is the active ingredient of a seidlitz powder and the amount ordinarily used for a dozen muffins is about half of an ordinary seidlitz powder. Another group of baking-powders is made of a combination of a phosphate salt with soda, and the third group is known as the alum powders. In each case the residue left in the muffin must be considered and as these are somewhat irritating to the intestinal tract, it is well always to use the best baking-powder obtainable and as little of that as possible. Three level teaspoons of baking-powder are sufficient for two cups of flour where one egg is used. Since a light mixture can be obtained by the action of air and moisture, both of which are far less expensive than any baking-powder, a premium is put on the cook who can handle her mixture lightly and quickly.

Soda and sour milk

Baking-powders

If a small amount of baking-powder is put in a tumbler and cold water added to it, it will be seen that the action causing an effervescence of gas takes place immediately. This is true in the flour mixture, the gas is given off just as soon as the liquid is combined with the dry ingredients. Since then the gas is desired in the mixture in the oven, it is well not to add the liquid to the dry ingredients until the pans are greased and the oven is ready to receive them.

Another way of forming carbon dioxide in our flour mixtures is by the action of yeast. The gas formed is exactly the same as that formed from baking-powders but it is formed in an entirely different way. Yeast is a tiny single-celled plant introduced into the dough where it finds plenty of food and conditions just right for growth. Like any other plant it must have warmth, moisture, mineral matter, protein food, and carbohydrate in order to thrive. These are all found in a mixture of wheat flour and water. The yeast cannot utilize the starch of the flour until that has been changed into the soluble form of sugar. This is done by the process of fermentation which the yeast itself is able to perform by the secretion of ferments during its growth process. It also is able to change the sugar thus formed to alcohol and carbon dioxide. It is a greedy little plant and changes far more starch to carbon dioxide than it needs for food, so that we can see the bubbles of gas forming in the dough while it is rising.

Yeast

There are many more chemical changes involved in the process of making bread but this is not the place to go into them thoroughly. Each step in the process of bread-making is done with some definite aim in mind. The reason the milk is scalded or the water boiled before starting our dough is in order to sterilize it to prevent other micro-organisms from growing under the same conditions as are being prepared for the yeast. If this were not done, sour bread might be the result. When bread is baked, the yeast plant is killed, leaving nothing in the bread but dead yeast cells which are organic material and therefore harmless. The carbon dioxide gas is expanded and driven out; so also is the alcohol that has been formed. The gluten present in the wheat flour being elastic stretches with the expansion of the gas until it is hardened by the action of the heat of the oven. The starch on the inside of the loaf unites with the water present to form hydrolized starch while that on the outside becomes dextrinized in the greater heat thus giving to the loaf its shiny brown appearance. At the same time flavors are developed due to the formation of a small amount of ethereal salts.