The Basics of Yeast
The yeast used in cooking and brewing is the single-celled fungal organism Saccharomyces cerevisiae. It multiplies rapidly when fed sugar in a moist environment. Yeast also thrives on starch, which it converts to glucose, a simple sugar. This process ferments the sugar, which converts to alcohol and carbon dioxide. The carbon dioxide expands baked good to produce the light, fluffy texture.
When used in baking, the minimal alcohol produced burns off and the yeast dies also with the heat. Yeast is also a vital part of the making of alcoholic beverages, such as beer and wine. In those processes, the liquid is not heated and the alcohol is retained.
Kneading yeast bread dough helps distribute the yeast cells uniformly throughout the dough, so it does not rise unevenly. Kneading also develops a firm gluten structure, providing the framework for the carbon dioxide bubbles.
Types of Yeast for Leavening
Dry active yeast is sold in single-use packets or bulk bags. Standard single-use packets contain about 2.5 teaspoons (1/4 ounce) of yeast granules. If the dry yeast is stored in airtight packaging, in a cool dry place, it is not necessary to refrigerate it. However, even this form of yeast will lose its life over time. Yeast should always be at room temperature to begin a recipe. Dried yeast has become the norm for its staying power in the pantry.
Fast-rising active dry yeast is smaller-grained than conventional active dry yeast and speeds rising times by as much as 50 percent, often eliminating the need for a second rising period. It may be used interchangeably, measure for measure, with active dry yeast. The best method for using this yeast is to mix it directly with the dry ingredients before adding liquid, instead of adding it to warmed liquid and then adding to dry ingredients.
Compressed fresh yeast consists of 70 percent moisture and must be stored in the refrigerator. Compressed fresh yeast is highly perishable, as opposed to dry active yeast, and loses its vitality within two weeks, even when properly stored refrigerated in an airtight container. Compressed yeast can be stored in the freezer, but should be defrosted at room temperature and then used immediately. Compressed fresh yeast is difficult to find in the United States. Use 2 teaspoons of dried yeast to a 2/3 ounce compressed yeast cake as a substitution.
You should proof your yeast to be sure it is viable before using in a recipe. To check it, mix a bit into 1/4 cup of lukewarm water with 1/4 teaspoon sugar. It should begin to bubble and ferment within about 5 to 10 minutes. If not, the yeast is dead and should be discarded.
Conditions for Using Yeast in Leavening
The ideal temperature for yeast growth is 100 to 115 F, but for leavening purposes, the ideal temperature is 80 to 95 F. If the yeast grows too quickly, it will produce large bubble pockets in the end product.
Yeast begins to die at 120 F. So, it is important to let your yeast dough rise in a spot where the temperature is regulated. One-half an ounce of yeast will raise 4 cups of flour in about 1.5 to two hours, under ideal conditions.
Salt inhibits the growth of yeast. Never mix yeast into salted water. Since most tap water goes through a filtering process which utilizes salt as a refining and cleaning agent, many cooks use only distilled water for baking. However, if you are baking during the hot summer season and find your dough rising too much, the addition of a little extra salt can control that runaway yeast growth.
Yeast measures will also have to be adjusted at higher altitudes. Again, this will take experimentation on your part for your altitude.
Salt and Sugar in Yeast Baked Goods
Although salt inhibits the growth of yeast, it does give a firmer crust, a finer crumb, and adds flavor. Sugars are not essential to leaven baked goods, but they make the product more tender due to the postponement of protein coagulation, allowing the dough or batter to grow to a greater volume before being frozen into stasis by the baking process, as well as adding flavor. If too much sugar is used, it can slow down the growth of the yeast, with a low-rise result. The relationship of sugar to salt to leavening is crucial to a pleasing final product.