Changes

Ever since people domesticated cereals (or maybe it was the other way around), they have known that if you grind the grains down into flour, then mix the flour with water into dough and bake it, then you'll get a flat, crumbly brittle bread like roti, pita or matzo. But if you leave the dough in a warm place for a few hours before baking it, then it will start to bubble and rise; and if you then bake it, the bread will be soft, fluffy, pleasantly tart and aromatic. Beer, another cereal product, has been known about as long as bread. And it's been also known for a long time that if you gather the froth from the surface of fermenting brew and add it to the bread dough, then it will rise faster.