Question

pickles are not kept in aluminium vessels why?

Answer 1

It is possible to store acidic liquids and foods inside aluminium containers (like it is done for sodas, fish cans etc.). The aluminium is protected with a polymer coating to prevent unwanted reaction and release of aluminium ions into the food. Depending on the type / thickness of the coating, time of storage and reactivity of the food it can happen that the coating will fail at some point.