Kitchen and everyday life · First steps · about 10 minutes
Store Leftovers Safely
Leftovers save money and time, but they need to get cold fast. Bacteria multiply quickly in food left at room temperature. These steps follow USDA advice for cooling, storing and reheating leftovers.
When to teach it: Watch from about 5, help pack leftovers from about 7, and put food away alone from about 10.
You'll need
- Shallow containers with lids
- Tape or labels and a marker
- Appliance thermometer for the fridge and freezer
- Food thermometer for reheating
Before you start
- Use an appliance thermometer to check that your fridge is at 40 °F or below and your freezer is at 0 °F or below.
Step by step
Tick each step as you go if you like; ticks stay on this device.
Biology
How it works: The danger zone and doubling bacteria
Bacteria grow fastest between 40 °F and 140 °F. Food safety experts call this the danger zone. In that range, the number of bacteria can double in as little as 20 minutes.
Doubling adds up fast. Start with 10 bacteria. After 20 minutes there could be 20, then 40, then 80. Two hours holds six 20-minute doublings, so 10 could become 10 × 2⁶ = 640. That's why the 2-hour rule exists.
Cold slows bacteria down, and freezing makes them go dormant, like they're asleep. Freezing doesn't kill them. When food thaws, they wake up and can multiply again. Some bacteria also make toxins that heat can't destroy, so reheating can't rescue food that sat out too long.
Shallow containers help because heat escapes through the food's surface. A thin, wide layer has lots of surface for its size, so its middle cools fast. A deep pot keeps its center warm for a long time.
bacteria = starting number × 2ⁿ, where n is the number of 20-minute doublings
Try it: Make a doubling chart on paper. Put 1 dried bean in the first square. Each new square gets double the beans of the one before. Stop after 6 doublings, which is 2 hours in the danger zone. How many beans are in the last square?
Keep learning: Science
Teaching it to your kids
- Set a 2-hour timer when food comes off the stove and put your child in charge of it.
- Let them pick the containers and write the labels.
- Show them the fridge thermometer and have them check it once a week.
Tips
- Small portions cool faster and are easier to reheat.
- Cooked rice that sits out too long is a common cause of one type of food poisoning, so get it into a shallow container and into the fridge quickly.
- Takeout and restaurant leftovers follow the same 2-hour rule.
- Freezing keeps food safe, but it doesn't kill germs. Treat thawed food like fresh perishable food.
Common mistakes
| Mistake | Instead |
|---|---|
| Leaving a big pot of soup on the stove to cool overnight. | Split it into shallow containers and refrigerate within 2 hours. |
| Reheating only until it's warm. | Heat to 165 °F and check in several spots. |
| Thawing leftovers on the counter. | Thaw in the fridge, in cold water in a sealed bag, or in the microwave. |
| Keeping leftovers for a week or more. | Eat them within 3 to 4 days, or freeze them. |
| Not knowing how cold the fridge is. | Keep an appliance thermometer inside and make sure it reads 40 °F or below. |
Safe habits
- Refrigerate perishable food within 2 hours, or within 1 hour if it's above 90 °F.
- Keep the fridge at 40 °F or below and the freezer at 0 °F or below.
- Reheat leftovers to 165 °F. Bring sauces, soups and gravy to a rolling boil.
Sources
Free how-to guides for families, with nothing to earn, pass or send in. They follow U.S. rules and sources; your owner's manual, product labels and state and local rules come first.