Cans can rust. They is metal. To prevent rust, the cans are coated on the inside with a plastic based product. However, the chemicals in the liquid soda drink can react with the plastic coating. Stuff happens. It is called chemistry. It is best to store a can upright so that the sealant of the lid does not interact with the soda itself. Lid interaction seems to especially bad. The sugar of the soda itself is actually used to keep rust and bad interaction down. "Rust" is a book by Jonathan Waldman. See, you don't have to read my blogs just for spiritual issues. Enjoy your next plastic, I mean soda drink! Yikes, in Boulder, our rectory stores the cola cans on their side.