Question

why should curd and sour substance not to be kept in brass and copper vessels?

Answer 1

Curd contains lactic acid because it is sour in taste. We know that metals react with acids to form salts and hydrogen gas. When curd and other sour substances are kept in copper vessel (metal), copper reacts with the acid in it to form hydrogen gas and toxic substances which are unhealthy and unfit for human consumption. It may cause food poisoning also