The process of heating, cooling and heating again leaves perishable foods vulnerable to bacterial contamination. These bacteria thrive in temperatures within the danger zone -- 40 to 140 degrees Fahrenheit. Once cooked, food is held in the danger zone during serving, up until the time you pop it in the refrigerator. To be safe from foodborne illness, limit your reheating of leftovers to one time only, and make sure you follow the rules of safe handling -- time and temperature in particular.
The Safe Zone
Once cooked, hot food keeps in temperatures above 40 F for two hours before bacteria levels begin to rise to dangerous levels. If the surrounding air temperature is 90 F or above, food only keeps for one hour. As long as the cooked food is refrigerated within the one- to two-hour safe time, it is safe to reheat. The same goes for leftovers. Refrigerate them in a shallow, airtight container within the safe period, and they live to be reheated another day.
Time in the Fridge
Placing cooked food in the refrigerator does not kill bacteria; it only slows its growth. The longer the food is in the refrigerator, the more likely bacteria is to multiply. Leftovers are safe to refrigerate for up to four days. Within this time either reheat or throw them away. If you opt to reheat within the safe time, keep in mind that all leftovers must be reheated to a safe temperature to kill bacteria.
Each time you reheat leftovers, do so to the recommended temperature that will kill bacteria. The U.S. Department of Agriculture recommends heating all leftovers to a safe internal temperature of 165 F before serving. Do not rely on your senses to determine whether your leftovers are heated to the recommended temperature. Press a meat thermometer into the thickest part of the leftovers to determine done-ness. If the reading is less than 165 F, continue reheating.
Freezing in Between
If you want your leftovers to last longer, pop them in the freezer instead of the refrigerator during the safe period. Inside airtight freezer bags or containers, leftovers remain safe to eat indefinitely, with quality diminishing within approximately four months. Transfer the leftovers from the freezer to the refrigerator the day before you plan to reheat them to give them plenty of time to thaw.
Food for Thought
If you do not consume all of the reheated leftovers, throw them away. Each time you cook food, allow it to cool, and then heat it back up, bacteria has the opportunity to multiply to dangerous levels. Consuming this bacteria may lead to foodborne illness. For foods such as soups or casseroles that are stored in abundance, scoop out and reheat only as much as you can eat in one sitting.
- U.S. Department of Agriculture: Leftovers and Food Safety
- U.S. Department of Agriculture: Danger Zone (40 F – 140 F)
- Foodsafety.gov: The Good, the Bad, the Reheated: Cooking and Handling Leftovers
- Elmbridge Borough Council: Food Safety Myths
- Risk: A Practical Guide for Deciding What's Really Safe and What's Dangerous in the World Around You; David Ropeik
- Photo Credit Creatas Images/Creatas/Getty Images