.25 ounces of active dry yeast

Active dry yeast is a leavening agent composed of dormant cells of the fungus Saccharomyces cerevisiae, dehydrated and granulated for shelf stability and long-term storage. The yeast cells are living organisms that remain metabolically inactive until rehydrated and exposed to warmth and food (sugars and starches). Each granule contains millions of individual yeast cells surrounded by a protective coating of inert materials and dead yeast cells, which allows the ingredient to retain viability for months to years when stored properly in cool, dry conditions.

When activated by mixing with warm water (typically 105-110°F / 40-43°C) and a food source such as sugar or flour, the dormant cells rehydrate and resume metabolic activity, producing carbon dioxide gas as a byproduct of fermentation. This gas creates the rise and airy crumb structure characteristic of yeast-leavened breads and baked goods.

Active dry yeast is the primary leavening agent in bread baking, pizza dough, sweet yeast doughs, and other fermented baked goods across nearly all culinary traditions. It is typically dissolved or "bloomed" in warm water, sometimes with a pinch of sugar, before incorporation into dough to ensure even distribution and activate the cells. The ingredient is essential in French, Italian, and Central European bread traditions, as well as in enriched doughs for cinnamon rolls, brioche, and panettone. Beyond baking, active dry yeast is occasionally used in brewing and fermentation of non-alcoholic beverages. Proper hydration temperature is critical—water above 120°F kills the yeast, while water below 70°F will not activate it efficiently.