Question

Why should curd and other sour foodstuffs (like lemon juice, etc.) not be kept in metal containers (such as copper and brass vessels)?

Answer 1

 Curd and other foodstuffs (such as lemon juice) are acidic in nature. Acids react with metals to give hydrogen gas. Hence, when these acidic foodstuffs are kept in metal containers, hydrogen gas is liberated, and it spoils the food and makes it inedible.