Timothy F. Lewis
TVWBB 1-Star Olympian
It won’t for exactly the material you are using, foil (aluminum) will cause the graying reaction. Glass and plastic will not.That could be but I never noticed a potato casserole ( like Kugela ) turning grey in a corning ware dish with a plastic wrap cover.
Only in a foil pan with a foil top.
Weird...
They are INERT material, hence the fabulous advantage of using Corning Ware!
Potato casseroles also, generally, are often fairly well coated with fats (butter, cheese, chicken fat, what have you) which provide an oxidation barrier.
Foil will cause a galvanic reaction, even more if you use a steel pan and foil with any kind of barely acidic medium.
Think about a potato battery.