Baker's Yeast

Baker's yeast is a microscopic fungus, which as a by-product of its existence, makes bread rise.

Waiting-on-yeast is to feed, keep house, keep it warm, clean its air, empty its garbage, and cater to its whims. Getting angry at its failings does not help. To provide patient loving care and food for growth does. Begin by dissolving the dry yeast in lukewarm water 90 to 105º F. At temperatures much higher than 105º, the yeast becomes very frantically active and soon exhausts itself; at lower temperatures it lives a more dormant existence, until below freezing, it barely respirates.

Yeast needs oxygen to breathe and simple sugars to eat. Though some simple sugars are present in flour, due to action of enzymes on complexer starch molecules, generally some sweetening is added for the yeast to dine on. Treat it to molasses: mild or a little blackstrap; honey: avocado, buckwheat, tupolo, or choice fancy; brown or white sugars; corn syrup. Living yeast turns oxygen and sugars into carbon dioxide and alcohols. (Brewers' yeast is an even better alcohol producer.) The carbon dioxide becoming trapped in the glutenous network of dough is what makes the bread rise. 

Take care that the carbon dioxide and the alcohols do not build up extensively enough that the yeast suffocates and generally expires in its own wastes. Punching down the dough or otherwise working with it releases gaseous by-products of the yeast existence and freshens its air. Bake the bread and the yeast dies. Slice it, butter it, eat it. Be thankful.

---The Tassajara Bread Book---