Instant dry yeast (IDY), like active dry yeast, has a low moisture content (5 to 7 percent) but instant dry yeast has a coating of ascorbic acid, developed by European bakers, which cuts production time. It needs no initial proofing and is mixed directly into the dry ingredients. The word instant simply means that the yeast can be added to the dough immediately without the usual hydration step needed for active dry yeast. Instant dry yeast cannot be mixed directly with ice cold liquids or into very cold doughs. It can be substituted for fresh yeast by using 40 percent of the amount of fresh yeast called for in a formula. Because of its stable shelf life (up to 2 years when properly stored), instant dry yeast is the yeast most frequently used by artisanal bread bakers. When marketing instant dry yeast to the home baker, a manufacturer might give it a different name, such as rapid-rise, quick-rise, fast-rise, and so forth.
