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Strange holes in aluminium foil

I currently work in a restaurant. When we put aluminium foil over a pan of mac & cheese a few days later the foils has holes in it. This still happens even when we put a sheet of wax paper between the mac and the foil. The mac is the only thing that does this. I'm in school for chemical engineering but i can't think of a reason of what would cause these holes to appear. Any ideas AskScience?
gpt
Aluminum has a very low reduction potential.  Much lower than steel, which the pan is almost certainly made from.  You are basically making a battery with the two metals.  

The steel (or one of the other metals in the pan) is getting oxidized by the food.  These ions then steal the available electrons off of an aluminum atom, oxidizing the aluminum.  The oxidized aluminum turns into aluminum oxide, probably, which is brittle and separates from the foil.  Keep going with this and you end up with a hole.  

The wax paper barrier isn't completely insulating the steel from the aluminum.  Even if it was, they might still both be touching a metal object in the fridge.  Try totally wrapping the pan in wax paper, then foil, then putting the thing on a plastic tray in the fridge.  Betcha the foil won't get holes in it then.