1. If the dish stewed in casserole is heated for a long time, protein, an animal raw material, will be degraded, its hydration capacity will be weakened, and a large amount of gelatinous liquid will be precipitated, which will increase its toughness. It tastes bad and is not easy to digest and absorb. Casserole stew will lose a lot of minerals and vitamins. In addition, the casserole stew has good sealing performance, and the odor substances in the original flavor are not easy to overflow. Some low-fat and valeric acid will remain in soup and raw materials, which will generate harmful substances when heated.

2. When brown or black spots appear on the surface of sweet potato, it means that it is polluted by black spot bacteria. The toxin discharged by Alternaria alternata contains sweet potato ketol and sweet potato ketol, which will make sweet potato hard and bitter, and bring different degrees of damage to the liver. Even boiling, steaming and baking can't destroy its physiological activity, so sweet potatoes with black spots can't be eaten.

3. Too hot drinks can cause extensive damage to skin and mucous membrane. Because protein is degraded at about 43℃, the gastrointestinal mucosa has been irreversibly degraded at 60℃. Drinking too hot drinks and porridge will lead to the death of blood cells or cultured cells.