By Harold McGee
The baker can incorporate yeast in very different forms and proportions. For a simple dough to be fully leavened and baked in a few hours, the standard proportion for cake yeast is 0.5–4% of the flour weight, or 2.5–20 gm per pound/500 gm flour; for dried yeast, approximately half these numbers. If the dough is to be fermented slowly overnight, only 0.25% of flour weight, barely a gram per pound/500 gm is needed. (One gram still contains millions of yeast cells.) As a general rule, the less prepared yeast goes into the dough, and the longer dough is allowed to rise, the better the flavor of the finished bread. This is because the concentrated yeast has its own somewhat harsh flavor, and because the process of fermentation generates a variety of desirable flavor compounds.