You didn’t finish dinner, so you cover the scraps with some aluminum foil before stashing them in the refrigerator. We have come to think that if something shiny is covering our food, nothing can go wrong. Actually, a lot can go wrong. Aluminum foil — as the name suggests — is mostly aluminum — 95% of it — combined with iron and silicon to prevent puncture. The manufacturers press it between rollers to get it thin. There are, unfortunately, a few problems associated with wrapping leftovers in foil, and they all involve food safety. The aluminum foil itself won’t hasten bacterial growth, but the way it covers dishes can. Even though you carefully crimp it, the foil doesn’t form an airtight seal, so air gets in. That makes it easy to bacteria to grow more rapidly. Staph and Bacillus cereus are two kinds of bacteria that need air to grow and multiply, and these germs aren’t killed by reheating food to high temperatures. Another problem is that foil traps heat, which speeds up spoilage. If you’re storing hot leftovers, wait until they’ve cooled down completely before you go wrapping them in foil. You also have to consider that aluminum might leech into your food. Acidic meals like spaghetti with tomato sauce can cause foil to degrade, potentially letting aluminum leech into your food. Because aluminum is a known neurotoxin, it can accumulate in the brain and central nervous system. Before you panic, there isn’t great evidence that wrapping foods in foil causes a significant problem. As long as your leftovers are low in the dish and the foil doesn’t touch them, it’s not a health concern. If there’s any chance the foil might brush your chili or chicken piccata, reach for the plastic wrap or a container instead. According to the FDA, the safest way to store most foods is in airtight containers with lids or sealable storage bags.
