Closing up leftovers in a sheet of aluminum foil and popping them in the fridge is a common practice. But before reaching for the Reynolds wrap, it is best to think again about the safest ways to store food for later.
Foil traps heat and doesn't create an airtight seal like other wraps and containers can. Food that sits too long in the temperature "danger zone" of 40–140 degrees Fahrenheit, like in some refrigerators, is susceptible to bacteria like salmonella and Staphylococcus aureus that can rapidly multiply when exposed to oxygen.
A tight seal with plastic cling wrap is one alternative for keeping pathogens out. Still, the best option — for both food safety and the planet — is to use shallow glass airtight containers, so food cools quickly, has minimal contact with the environment, and is easy to reheat.