Active dry yeast (ADY) is composed of tiny, dehydrated granules that are alive but dormant because of lack of moisture (moisture content is 5 to 7 percent). When mixed with warm (105°F–115°F / 42°C–47°C) liquid, the yeast will activate. Active dry yeast is available as regular or quick-rise, with the latter taking about half as long to do its leavening work. Each type can, however, be used interchangeably with an adjustment to the amount of yeast used. Both types should be stored in a cool, dry place and can be refrigerated; however the yeast should be brought to room temperature (68°F-77°F / 20°C–25°C) before using. Although the general recommendation for substituting active dry yeast for fresh yeast in a formula is one part dry to two parts fresh, it is always best to check the manufacturer’s package directions. Active dry yeast must be rehydrated in four times its weight of 105°F-115°F (42°C–47°C) water. To test whether active dry yeast is viable, dissolve it in warm water with a pinch of sugar and set it aside in a warm spot for 10 minutes. If the mixture begins to foam and swell, the yeast can still do its leavening job.
