Aluminum foil allows foods to stay crisp in the refrigerator because it has a very low moisture transfer rate. Pizza stored in a plastic bag may get soggy and that bag will show visible moisture gathering inside. Aluminum foil does not gather moisture and the pizza crust stays crisp. Foil prevents harmful bacteria that can cause illness from affecting refrigerated or stored food by keeping it fresh and dry. Use foil to wrap sandwiches that go in the refrigerator and cover containers that have no lids. Use the shiny side out to reflect warm temperatures away.
Aluminum also creates a moisture- and bacteria-free environment for frozen foods. It also keeps the smell of food in the foil so it does not contaminate the whole freezer. Wrap the food in plastic wrap first, then wrap in foil for extra protection or wrap in foil first then butcher or wax paper. Take a piece of foil large enough to entirely wrap the food with a little left over. The fewer seams in the foil the better. Place food in the center and bring two edges on opposite sides together. Roll down the excess foil and flatten the seam against the food. Tape with freezer tape. Avoid regular tape because it will not stick in the freezer. Flatten the two ends and fold to make a point as if wrapping a gift, and bring both sides up toward the seam removing as much air as possible. Use tape to secure each side. Use heavy-duty foil for best results in freezing. One little hole will cause the entire piece of food to be ruined and foil tears easily. According to Reynolds Kitchens, it does not matter which side, shiny or dull, is used against the food.
Do not wrap tomatoes, berries or other acidic foods in foil. The aluminum causes a chemical reaction resulting in a blue residue on the food or little black spots. Other reactions occur when using on highly salted foods or foods that have vinegar in them. The reaction may cause the foil to malfunction and allow moisture and bacteria inside.
Aluminium foil can be reused safely as long as it is washed off well and dried before wrapping food in it. Avoid using foil that has holes in it because it can allow moisture to set in and bacteria to grow.