Yeast is a single-cell organism, called Saccharomyces cerevisiae, which needs food, warmth, and moisture to thrive. It converts its food—sugar and starch—through fermentation, into carbon dioxide and alcohol. It's the carbon dioxide that makes baked goods rise.
Yeast is an important ingredient in baking as well as beer brewing. There are two types of yeast available for sale: One type is brewer's yeast, a wet yeast used primarily in beer making. The other type is baker's yeast, which is used as a leavening agent. There are then two types of baker's yeast—fresh yeast and active dry yeast. The three most common brands of yeast you may find in your local supermarket are Fleischmann's Yeast, Red Star, and SAF Perfect Rise Yeast.
Fresh yeast, also called wet, cake, and compressed yeast, comes in small square cakes that are made of fresh yeast cells. These blocks of fresh yeast, often used by professional bakers, are comprised of 70 percent moisture, and therefore are quite perishable. If not used right away, fresh yeast can be stored in the refrigerator for up to only 3 days, so it should be bought in amounts that will be used quickly.
The fresh yeast cake has a stronger smell than dry yeast. It is light beige in color and soft and crumbly in texture. Since it is highly perishable, fresh yeast cakes are stored in the dairy case near the butter, but may not be available in your local supermarket. Depending on the manufacturer, such as Fleischmann’s, one cake of fresh yeast equals one envelope of dry yeast. Otherwise, the conversion is 2/3 ounce of fresh yeast equals 2 1/4 teaspoons dry yeast. Fresh yeast is often more expensive than active dry yeast.
Dry yeast is the more convenient of the two types. It is granulated and comes in little 1/4-ounce packets (approximately 2 1/4 teaspoons) or loose in a jar. Once exposed to the air, it should be stored in the refrigerator.
There are two types of dry yeast: Active dry yeast and instant yeast. The only difference between the two are the size of the granules; active yeast has larger granules while instant has been ground into a finer texture. Instant is named as such because it can be added directly to other ingredients; it does not need to be dissolved in water before using as active dry yeast does. Active dry yeast is dormant until proofed, which occurs when it is dissolved in a small amount of lukewarm water (about 110 F).
Instant yeast is also available as rapid or quick rising. This type of yeast includes enzymes and additives to help the dough rise faster. When using rapid-rise yeast, it will take half of the time to make bread rise, or if the recipe calls for two sets of rising times, you can skip one of them and proceed to kneading and shaping the loaves.
Tips Using Yeast
Yeast is basically used in baking bread versus baked desserts; when making desserts, leavening agents such as baking soda and baking powder are used, or sometimes self-rising flour. However, there are a few dessert recipes that call for yeast such as Christmas breads and sweet rolls.
If you are unsure if your yeast is still alive, you can easily test it. Pour about 1/2 cup lukewarm water into a bowl and sprinkle over the yeast along with a pinch of sugar. Stir, and let sit for a few minutes; if it completely dissolves and the liquid bubbles, it means the yeast is active.
Yeast needs warm temperatures to do its thing, so when placing the dough to rise make sure it is sitting in a place that is 70 to 80 F. And if your recipe includes a lot of eggs, butter, sugar, and milk, you may need a little more patience; these ingredients slow down the leavening process.
You can store yeast in the freezer, which will pause its activity and prolong its shelf life. Just be sure to place it in a well-sealed container before freezing.