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

Curd and sour substances should not be kept in brass and copper vessels because these metals react with the acids present in such substances. The acidic components like lactic acid in curd or citric/tartaric/acetic acids in sour foods chemically react with copper and zinc (present in brass), leaching metal ions and forming toxic metal salts, such as copper sulfate and zinc acetate. These compounds are harmful to health if ingested. Additionally, the reaction can cause corrosion of the vessels and the release of hydrogen gas. Consuming foods contaminated with these metal salts can lead to symptoms like nausea, vomiting, stomach cramps, and in severe cases, liver and kidney damage. This is why acidic foods are unsafe to store in brass or copper vessels unless they have a protective lining.