Alum, also known as potassium aluminum sulfate dodecahydrate, has been banned as a food additive by the state. Alum is a double salt of potassium sulfate and aluminum sulfate containing crystallization water.

Colorless cubic crystals are usually octahedral in appearance, or form polygons with cubes and rhombic dodecahedrons. Sometimes 1 1 1 is attached to the container wall and looks like a hexagonal plate, which belongs to α-alum double salt and has glass luster.

The density is 1.757g/cm3, and the melting point is 92.5℃. At 92.5℃, it loses 9 molecules of crystal water, and at 200℃, it loses 12 molecules of crystal water, which is soluble in water and insoluble in ethanol. Alum tastes sour and poisonous.

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Food additives containing aluminum may be used in the processing of fried dough sticks, steamed bread, noodles and puffed food, which will do great harm to human body, especially to children's growth and intelligence. ?

Five departments, including the National Health Planning Commission, stipulated that from July 1 day, 2065438, flour products such as steamed bread and scones (except fried flour products, batter for hanging paste, wrapped powder and fried powder) could not be added with aluminum-containing leavening agents such as potassium aluminum sulfate and ammonium aluminum sulfate, also known as alum, and baking powder, the main components of composite leavening agents, were also the above two substances. In puffed food, it is no longer allowed to use any food additives containing aluminum.

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