Handling and using yeast

Here are a few tips to keep in mind when handling yeast.

• Active dry can be used at 50% of the weight of fresh yeast.  Instant dry can be used at 40% of the weight of fresh yeast.
• Yeast responds to warm water only. 
• It is extremely sensitive to cold temperatures, too much air, and too much heat.  
• Yeast dies within a couple of hours. Though most of the yeast is dead by the time the bread is placed in the oven to bake, there is still enough active yeast to produce carbon dioxide during the early stages of baking. Bread continues to rise in the early stages of baking, but as it progresses, the high temperature kills off the remainder yeast. Most bread deflates slightly toward the end of baking.
• A few things inhibit the yeast's ability to ferment. Salt, shortening, and animal fats can affect the rising action. Recipes that use yeast as the leavening agent, usually contain small amounts of salt and have some sugar for balance.
• Inactivated or dry yeast may at times be dead before use. To check for vitality, add a package to warm water and watch for gas production or expansion. Only after that, combine yeast with flour. Yeast will not activate if the water is too hot, too cold, or if a liquid other than water is used (i.e. milk).

Remember that yeast is a living organism and that the rising action is a result of its metabolic activity.