The reason why curd and sour substances should not be kept in Brass and Copper vessels, as both the substances are acid in nature. Sour substances are those substances which have citric acid for instance: like lemon, limes, oranges etc. Further “an acid can be classified as strong or weak based on its reactivity, conductivity and pH level”. When the substance is keept in such containers acids react with metals to produce hydrogen gas and salt. Because of which the container will be corroded and the food also may get spoiled.
When the substance is kept in brass or copper it reacts and the the toxic element which is created may prove harmful for human body or may also cause food poisoning. That is the reason why we use stainless steal. Thus, it is advisable not to keep those substances in Brass or copper containers.