A zip-top bag can take leftovers from the fridge to the microwave, but check the box before you put lunch in to heat. A bag’s zipper tells you how it closes. The package tells you what the plastic was made to handle, whether that’s freezing, defrosting, or reheating.
Read the heating instructions before you seal up lunch
Ziploc’s FAQ says its bags can be used in the microwave to defrost or reheat food. That guidance is specific to the brand and those uses. Check your particular box for directions, including how to vent the bag. If the package gives no microwave directions, transfer the food to a microwave-safe bowl before heating.
The brand also flags foods with a lot of fat or sugar because they can heat fast. If you packed a sticky glaze or oily sauce, using a bowl makes it easier to stir and check how hot the food is as you go. A bowl also saves you from trying to pour steaming food out of a soft bag.
Give freezer bags the job they were made for
For portions you plan to freeze, look for bags labeled for freezer use. Freeze soup or sauce in meal-size portions and leave room at the top for the liquid to expand. If a bag tends to flop over while you fill it, set it upright in a bowl. Label it with the contents and date before putting it away.
The same label check works for other food packaging. The USDA’s guidance on food packaging explains that a container intended for cold storage, such as a cottage cheese tub, may be unsuitable for heating. If the original box is gone and you can’t identify the bag, use it for cold storage and grab a microwave-safe dish when it’s time to reheat.
