Question

why should curd and sour substances not be kept in brass and copper vessels

Answer 1

Curd and sour substances are acidic in nature and when kept in brass ar Cooper vessel ,then it reacts with it and to form the salt because acid and metal reacts to form the salts.Hence they are not kept in the brass or copper vessel

Answer 2

Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food.