Aluminum beverage cans are also lined with a thin layer of plastic that is sprayed inside after the can is formed. If they weren't this way, then acidic beverages would eat through the crazy-thin aluminum skin in fairly short order.

It's also one of the things that the beverage can manufacturing industry tests for. All aluminum beverage cans are tested optically to detect and reject individual cans with holes in the metal that light can penetrate, and spot tests are also done using brine and electricity to detect metal exposure due to an incomplete plastic coating inside of the can (which can result in cans being rejected in batches of tens-of-thousands at once).

(Given all of this, maybe we had it closer right with the returnable, reusable glass bottles that were previously used by the soda industry.)