Choosing the correct plastic food-grade container involves reading the resin identification code inside a triangle on the back or bottom of the container to understand its intended use and determine if it is easy to recycle. Numbers 1, 2, 4 and 5 are safe to use for food, while the numbers 3, 6 and 7 indicate the use of nonfood-grade or single-use plastics that aren't appropriate for food storage.
Reusing plastic containers that are intended for a single use can cause harmful chemicals to leach into the food over time. They may not be easy to clean and encourage bacteria to grow in the container, such as in the screw top of a single-use water bottle or in the scratches on the bottom surface of a container. Some plastics do not withstand heat or cold; others, such as those marked with "PC," for polycarbonate, or "PVC," for polyvinyl chloride, can leach harmful chemicals into the food.
Food-grade zipper bags are the only plastic bags appropriate for storing foods. Wrapping food directly in grocery bags may leach harmful chemicals into the food.
Research indicates that many plastics once classified as safe to use for food storage leach harmful chemicals. The Natural Resources Defense Council recommends using glass, ceramic, stainless steel and stoneware as safe alternatives to plastic for storing foods.