Question

Why should not curd be kept in copper containers?

Answer 1

all acids are sour in nature.
curd,is made from milk which is slightly acidic in nature(as it contains lactic acid).we know that acids react easily with metals to give salt and hydrogen gas.
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.