The oven is the best choice for reheating mashed potatoes because you have very precise control over the temperature. You also can keep the potatoes covered to retain moisture so they don't dry out. But to keep your potatoes from turning to glue, you'll also need to add extra liquid and oil.
For best results, skip the microwave—the high heat tends to suck the moisture out of mashed potatoes—and reheat them on the stovetop or in the oven. But we do have tips for reheating in the microwave if you must.
Reheat in the Oven
Whether they're made with just potatoes, milk, butter, and salt or jazzed up with ingredients like sour cream or garlic, mashed potatoes will heat up wonderfully in the oven.
Time will depend on how big a dish of potatoes you are warming up. Oven: Preheat the oven to 375 degrees Fahrenheit, cover mashed potatoes with heavy foil in an oven-safe dish to keep them from drying out, and reheat at 375 for 30-40 minutes.
Usually, restaurants reheat mashed potatoes inside the crockpot for several hours. If you also want to try using this method at home, be mindful of signs of spoilage such as changes in texture or color when keeping it for long hours. Also, check the temperature setting when you reheat the dish to avoid overheating.
Whether reheating leftovers or using a recipe to make mashed potatoes ahead of time for a crowd, warming those spuds in a double boiler will do the trick. Alternatively, you can place your potatoes in a Pyrex glass bowl set over (but not in) simmering water.
Your other option would be placing the prepared mashed potatoes in a buttered, oven-safe dish (covered in aluminum foil) and sliding it into a 275- to 300-degree oven.
On the stove: Place leftover mashed potatoes in a pot with a tablespoon of butter and some milk. Warm the potatoes over low heat on the stove, being sure to give them a quick stir at least every minute. Once warm throughout, remove them from the heat and enjoy!
To reheat mashed potatoes in the oven:
Add a bit of butter, milk, or cream for extra moisture. Cover the dish with foil and bake for 10-15 minutes, stirring gently every 5 minutes. Once your bowl of potatoes is hot, at least 165°, you can serve and eat.
The microwave, it turns out, is actually perfect for reheating mashed potatoes. Simply add your mashed potatoes to a microwave-safe bowl, along with a tablespoon or so of milk or cream. Cover the bowl tightly with plastic wrap and microwave on 50 percent power for 60 seconds.
Mashed potatoes can be kept warm in a crockpot (if serving later the same day) OR refrigerated for up to 2 days. To reheat, place them in a large pot over medium-low heat, stirring constantly and adding additional milk/cream as needed to achieve the desired consistency.
When time is limited and mashed potatoes are a "must have" on the menu (which is always), keep the prepared potatoes warm by placing them in a heat-resistant bowl, covering, and setting it over a pot of simmering water. The potatoes should still be tasty 2 to 3 hours later.
How Long You Can Keep Leftover Mashed Potatoes. Mashed potatoes should easily last three to five days in the fridge if stored correctly and within two hours of cooking. This means ensuring there isn't any moisture buildup under the lid that could encourage the growth of bacteria.
The best way to heat them is on the stovetop.
Put the spuds in a sauce pan over medium heat and stir until hot all the way through. You can also opt for the oven (350 degrees F for 30 minutes) or slow cooker (set to low for 2 to 4 hours) methods but we'd advise against the microwave, which will dry them out.
MASHED POTATOES
If you are using a convection oven, heat to 325 degrees. Your mashed potatoes have been packaged in an oven safe tin, making them easy for you to re-heat. Remove the container cover and re-cover the container with a sheet of aluminum foil to maintain moisture, and then place in the oven for 15 minutes.
If food has been hygienically prepared, cooled quickly after cooking (or reheating) and stored cold, reheating more than once should not increase the risk of illness.
Cool, cover, and refrigerate potatoes in a microwave-safe, airtight container for up to 2 days. Thirty minutes before serving, microwave until warm.
Mosley's verdict is clear cut: “You can actually reheat your leftovers as many times as you like, as long as you make sure every morsel is piping hot all the way through,” he says. SBS Food put the matter to Lydia Buchtmann, spokesperson for the Food Safety Information Council, who agreed.
You can use what you have on hand: Flour, cornstarch, or powdered milk are all solid options that are probably already in your pantry. For what it's worth, we recommend sticking with cornstarch—it has twice the thickening power of flour and it's safe for gluten-free diets.
Mashed potatoes can sit out for two hours at room temperature. Any longer than that, they can enter the “danger zone,” which are unsafe temperatures that promote the growth of bacteria. If temperatures go above 90 °F, mashed potatoes can only sit out for one hour.
Reheating mashed potatoes in a slow cooker or Crockpot ⇢ Making use of a slow cooker or Crockpot is a great option if you're low on oven space on Thanksgiving Day! Transfer the potatoes to your slow cooker & reheat with the low setting for 3-4 hours.
Can I eat refrigerated mashed potato? - Quora. Sure you can eat leftover mashed potatoes. Be warned, they're never as good as freshly prepared mash though.
Move the potatoes to a baking dish: Heating the potatoes in an even layer allows them to warm up faster with less drying out. Add more cream and butter: More moisture and fat are the two secret ingredients to reheating any leftovers. For potatoes, reach for half-and-half or broth and butter.
Keep Your Potatoes Hot
If you want a truly creamy taste and texture, you can't let the potatoes cool before mashing—you want to start getting busy with them as soon as possible after they've been boiled and drained.
The Oven Method
You can also add a bit of milk or cream to your cold mash, place them in a buttered oven-safe container, cover with foil, and heat in a 325-degree oven. I check frequently, stir occasionally, and add more dairy as needed, but this reheating method should take about 30 minutes total, give or take.