Browsing through old cookbooks can be a lot of fun for cooks and bakers. Some of the instructions are often a bit outdated -- few modern chicken recipes start with killing the chicken, for example -- but most basic recipes and techniques are surprisingly timeless. The same doesn't necessarily hold true with ingredients, so when a recipe specifies something unfamiliar, such as double-acting baking powder, you might wonder whether your modern baking powder is appropriate. In this instance, it certainly is.
Quick and Dry
Baking powder is based on baking soda, a pure and slightly alkaline chemical that came to popularity in the 19th century. Instead of yeast-based starters or quirky leavening agents such as burnt deer antlers, bakers could use baking soda to make their biscuits, muffins and quick breads light and fluffy in mere minutes. The soda reacted chemically with acidic ingredients such as buttermilk, producing fine bubbles of carbon dioxide that lightened and leavened the dough or batter. In the heat of the oven, the bubbles expanded, and the carbon dioxide cooked out and left well-risen baked goods to enjoy.
A Question of Balance
The only problem with baking soda was that bakers sometimes had difficulty in finding the correct balance of soda and acidic ingredients. Too much soda or too little acidity left unused soda in the batter, where it added an unpleasantly soapy, chemical taste to the baked goods. Too little soda meant your baked goods wouldn't rise properly, while too much acidity might leave the baked goods pale and with an unpleasant tang. Eventually, manufacturers hit on the notion of mixing baking soda with pre-measured quantities of a dry acidic ingredient, such as cream of tartar. That type of mixture became known as baking powder.
Single- vs. Double-Acting
You can make a simple baking powder at home by combining cream of tartar and baking soda, then stirring them into your recipe. As long as you bake your dough or batter immediately, you'll get an excellent result. That early type of baking powder was referred to as "single-acting," because all of its leavening power was generated immediately. That presented a problem if you weren't able to get your baked goods into the oven immediately, because your baking powder would expend most of its leavening power before they were baked. In response, manufacturers developed double-acting baking powders.
What Double-Acting Means
Double-acting baking powders still combine baking soda with a quick-acting acid, such as cream of tartar or monocalcium phosphate, but they also add a second acidic ingredient, such as sodium aluminum sulphate. This second acidic ingredient won't react chemically with the baking soda until it's heated, so even if you refrigerate a dough or batter overnight, it will still rise. The proportion of quick and delayed-acting ingredients varies between brands, but modern brands are all double-acting. You can use them freely in vintage recipes, even though the label might not specify that this is how they work.
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