5.2.2: Chemical Leavening
Baking Powder
Baking powder is a dependable, high-quality chemical leavening. To be effective, all baking powders rely on the reaction between one or more acids on sodium bicarbonate to produce carbon dioxide gas. Just as with yeast leavening, the presence of carbon dioxide gas creates air bubbles that cause the product to rise.
There are two main types of baking powders available on the market:
- Continuous or single-action baking powder
- Double- or multiple-action baking powder
The difference between continuous- and double-action baking powders is simply the rate of reaction:
- Continuous-action baking powder uses one acid, which continuously reacts with the soda to release gas steadily throughout the baking process until all the gassing power is spent.
- Double-action baking powder contains two different acids, which react with soda at different stages of the baking process. One acid reacts to give off a small amount of gas at low temperatures, and the other major acid reacts at baking temperatures to give off the bulk of the gas.
The Leavening Mechanism of Baking Powder
Before baking, approximately 15% of the CO 2 gas is released in the cold stage. Eighty-five percent of the CO 2 gas is released in the oven starting at approximately 105°F. Some leavening power is apparently lost in the cold stage, but there is usually still adequate gassing power in the remaining portion.
When the baking powder is activated through moisture and heat, the gas works its way into the many cells created by the mixing or creaming of the batter and starts to expand them. This process comes to a halt when the starch gelatinizes and the cells become rigid. This starts at about 140°F and is more or less complete at around 167°F. After this point, some gas may still be created, but it simply escapes through the porous structure of the product.
Using Baking Powder
For even distribution throughout the batter, the baking powder should be sifted with flour or other dry ingredients.
Sodium Bicarbonate
When sodium bicarbonate (baking soda) is moistened and heated, it releases carbon dioxide gas. If it is moistened and heated in the presence of sufficient acid, it will release twice as much gas as if it is moistened and heated without the presence of an acid.
Slightly acidic ingredients provide the mix with some of the necessary acids for the release of carbon dioxide gas. Examples are:
- Honey
- Molasses
- Ginger
- Cocoa
- Bran
For this reason, some of the mixes contain baking powder only while others contain a combination of baking powder and baking soda. If an excessive amount of baking soda is used in a cake batter without the presence of sufficient acid, the normally white cake crumb will have a yellowish-brown color and a strong undesirable smell of soda.
The gas evolves very fast at the beginning of baking when the pH level is still on the acidic side (pH of around 5 to 6). Once the soda neutralizes the acid, the dough or batter quickly becomes alkaline and the release of gas is reduced. Mixes and doughs leavened with baking soda must be handled without delay, or the release of the gas may be almost exhausted before the product reaches the oven.
The darker color of the crumb found on the bottom half of a cake or muffin is caused by the partial dehydration of the batter that is heated first during baking. In spiced honey cookies and gingerbread, baking soda is used alone to give them quick color during baking and yet keep the products soft.
The level of baking soda depends on the nature of the product and on the other ingredients in the formula. Cookies, for example, with high levels of fat and sugar, do not require much, if any, leavening.
Cream of Tartar
Cream of tartar is a white crystalline compound that exists in grapes, tamarinds, and other fruits. It is prepared from the sediments in wine barrels and is called argol . The argol is dissolved in hot water, and the coloring matter is removed by means of clay or egg albumin. After being purified by crystallization, it is ready for the market.
Cream of tartar has no leavening capacity by itself, but can be used in combination with sodium bicarbonate to provide the acid necessary for leavening. It was formerly used for making baking powder but that practice has been largely discontinued because of cost and its too quick reaction time. In some recipes, it is used alone. Cream of tartar is also an excellent stabilizer for egg whites.