active dry yeast [ak – tiv drahy yeest] noun
Saccharomyces cerevisiae. Also called baker’s yeast, not to be confused with instant yeast, rapid-rise yeast or quick-rise yeast. Active dry yeast is most commonly called for in home recipes where it is used to leaven baked goods. It is a microorganism that feeds on sugars present in recipes; it then creates carbon dioxide gas (air bubbles) which help baked goods rise and give them a light texture.
Active dry yeast can be found in jars, in bulk and most often, in small foil packets (three packets are usually attached to one another). One packet equals about 2¼ teaspoons of yeast, or ¼-ounce. You can find this yeast often in both the refrigerated section of the supermarket as well as on the shelf in the baking aisle. It needs to proof before being incorporated into a recipe, which is a technique where it is bloomed in lukewarm water (and sometimes a pinch of sugar). Suggested temperatures vary with brand but typically range between 100° and 115° F. If your water is too hot, it will kill the yeast, which is a living organism. For storage, follow brand recommendations, but an unopened package can typically be refrigerated for up to six months.