Fermented or leavened wheat, rye, oats, spelt and barley. When these grains come in contact with water, they leaven within 18 minutes. In the case of hot or salted water, leavening takes place instantly.
“Chametz” may not be consumed on “Pesach” either by eating or drinking, and may not be held in one’s possession, nor may any benefit be derived from “chametz.” Grain flour is commonly produced from grains that have been washed and tempered. Tempering is the process by which grains are softened by soaking in water, and this flour and all products made with it are, therefore, “chametz.”