Among the following, which is not the correct method for keeping the curd ?

Curd contains lactic acid, which gives it its characteristic sour taste. When curd is stored in a copper vessel (or brass), the acid reacts with the metal surface through a chemical process.

This reaction results in the formation of toxic metallic compounds, such as copper salts, which can make the curd unfit for consumption and potentially lead to food poisoning or digestive issues. On the other hand, stainless steel, glass, and food-grade plastic are non-reactive materials that do not undergo chemical changes when they come into contact with the mild organic acids found in food. Therefore, keeping curd in a copper vessel is considered an incorrect and unsafe method.