Mashed potatoes store well in both the freezer and the refrigerator. You can reheat refrigerated potatoes immediately, but frozen ones must be thawed overnight in the fridge first. Store the potatoes in individual serving size containers to make reheating simple, or in a family size container so you have a quick side dish available for last minute meals. Reheated mashed potatoes may appear watery at first, but stirring quickly returns them to their normal texture.
Place the mashed potatoes into a microwave-safe bowl. Cover the bowl loosely with microwave-safe plastic wrap or a paper towel.
Microwave the potatoes for 30 seconds for a single serving, or up to 1 1/2 minutes for larger portions.
Remove the plastic wrap slowly, to prevent burns from escaping steam. Stir the potatoes.
Return them to the microwave and continue to heat in 30 second to 1 1/2 minute increments until they are heated through. Stir the potatoes after each heating cycle to help them warm up evenly.
Heat the mashed potatoes until an instant-read thermometer reads 165 degrees Fahrenheit when inserted into the center of the potatoes. This temperature ensures that any illness-causing bacteria is dead.
You can also reheat mashed potatoes on the stovetop in a double boiler. Stir constantly and add a small amount of milk if they appear dry after reheating in this manner.