Question

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

Answer 1

when kept in copper or brass vessels,curd(and other acidic food items) reacts with copper and forms toxic compounds which may be unfit for human consumption,and may cause food poisoning.thus it is not advisable to keep curd and other acidic or sour food items in copper or brass vessels.

Answer 2

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