In cooking, the word “proof” has at least 3 meanings, all involving yeast in one way or another.
- A test you do to yeast to see if it is still alive. You do this either to yeast that you’re suspicious of, either because you’ve had it on hand a long time, or that you think the store might have had on hand since hoop skirts were fashionable. You mix the yeast in a small amount of lukewarm water (105 to 115 F / 40 to 46 C) with a pinch of sugar (as food), and let it stand for 5 to 10 minutes without disturbing it. If it produces foamy bubbles on top of the mixture, the yeast is good to use. If it doesn’t, get fresh yeast so that what you are intending to make with it doesn’t go horribly wrong.
- The stage during which you let finished yeast dough products rise in their final shape. A temperature between 90 and 105 F (32 to 40 C) and a humidity of 80 to 85% is ideal (generally, only professionals have this kind of control, using a proof box.) Breads and rolls that are baked in a steam environment are only let proof to 2/3 of their final size (the rest being achieved while cooking); breads and rolls being baked in normal, dry ovens are allowed to proof to their final size.
- A measurement of the amount of alcohol (generated by yeast) in something. See under Proof in the entry on Alcohol.