Why does foil get holes in it after wrapping some foods?

Aluminum foil can develop holes when it comes into contact with certain types of food. This is due to a process known as electrochemical corrosion, which occurs when two dissimilar metals come into contact with each other in the presence of an electrolyte. The electrolyte in this case is the moisture and salts present in food.

When food with a high salt content, such as cheese, ham, or bacon, is wrapped in aluminum foil, the salt molecules react with the aluminum atoms on the surface of the foil. This creates tiny holes in the foil, which can then become larger over time. The process is accelerated by the presence of an acidic environment, such as that created by vinegar or tomato sauce.

To avoid this problem, it is recommended to use plastic wrap or parchment paper instead of aluminum foil when wrapping foods that are high in salt or acidity.