Natural Yeast versus Commercial Yeast
We're using a sourdough starter to leaven the bread in this class, but many types of bread recipes call for commercial yeast. Just to clear up any misunderstandings, let's break down the differences between sourdough starter (or natural yeast), and commercial yeasts.
Fresh Yeast
Also called cake or compressed yeast, fresh yeast has a crumbly, soft texture that dissolves easily in warm liquid. Fresh yeast is a powerful leavener, but its short shelf life (about two weeks in the fridge) makes it impractical for most home uses. It is primarily used in bakeries and commercial kitchens.
Active Dry Yeast
Active dry yeast has been 95 percent dehydrated into tiny granules. This intense process damages some of the cells while others become dormant, so we “proof” the yeast in warm (about 110 degrees) water before adding it to the rest of the ingredients; the yeast will start to bubble when it activates. To substitute rapid-rise yeast in recipes that call for active dry, use 25 percent less than called for. All types of dry yeast stay fresh longer when stored in the refrigerator or freezer.
Instant Yeast
Also known as rapid-rise yeast, instant yeast is dehydrated to the same concentration as active dry, but by a gentler, less-damaging method. As a result, rapid-rise yeast can be mixed directly into other ingredients, and you can use less without a reduction in leavening. We prefer rapid-rise yeast in the test kitchen for its potency, convenience, and clean flavor. This yeast has a long shelf life and can be stored, unopened, for up to two years.
