Adding additional liquid, such as milk, plant-based milk, or vegetable broth can also help by keeping the potatoes from drying out. To reheat mashed potatoes in the oven: Place your leftover mashed potatoes in an oven-safe dish. Stir in melted butter, melted vegan butter, or oil and milk/cream, vegan milk, or broth.
Reheating in the Oven
If you are reheating them in the oven, stir in the liquid and butter pieces, then spread the potatoes out in a baking dish. Cover with aluminum foil to keep the potatoes from drying out. Reheat at 350˚F for 20 to 30 minutes, or until the potatoes reach 165˚F.
Take your mashed potatoes out of the fridge and set them on the counter for about 20 minutes to bring them to room temperature. Meanwhile, preheat the oven to 350°F. Then, pop them in the oven, covered, for about 15-20 minutes, or until warmed through.
Reheat on the Stovetop
She says to store them in a heatproof bowl after cooking; when it's time to warm them up, place the bowl over a pot of simmering water. Add an extra splash of cream or milk, and another pat of butter to ensure the mashed potatoes don't dry out.
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.
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.
Oven method:
If you refrigerated your mashed potatoes in an oven-safe casserole dish, set them out on the counter to take the chill off for at least 20 minutes before you pop them into the oven. When you're ready, bake, covered, at 350 degrees for 15 to 20 minutes, or until the potatoes are hot throughout.
If your mashed potatoes are done too soon, they could cool or dry out before the meal. Start the potatoes during the last hour of cooking, when you start the gravy. If that's too much, keep mashed potatoes warm in a slow cooker. Stir in a little warm milk or butter for added moisture.
The speediest way to reheat a baked potato is in the microwave, so if you're in a pinch, this is the method for you. We recommend cutting the potato in half and covering the cut sides with a damp paper towel, so that they warm all the way through and don't dry out.
If stored correctly in plastic containers, leftover mashed potatoes can last 3 to 5 days in the fridge. Just make sure the leftovers are stored in a sealed container. An airtight container will keep the moisture inside the container and keep the potatoes from drying out.
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.
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.
Texture: Texture is another sign of whether mashed potatoes have gone bad. If the mashed potatoes are slimy or have a watery consistency, they should be discarded. Additionally, if the mashed potatoes are hard and dry, they may be stale and not suitable for consumption.
If they're undercooked, you'll have pockets of crispy potato chunks-—a big no-no for classic fluffy mashed potatoes. If you overcook them they disintegrate and your potatoes will be soupy.
Don't over-mixing: I can't say it enough, DON'T mash the potatoes to much! As you mix potatoes it causes them to release their starch, which is necessary for creamy mashed potatoes, but too much mixing releases too much starch, and causes thick and gluey mashed potatoes.
Mashed potatoes(Cooked and refrigerated) will last 3 to 4 days. Raw potatoes(cut and stored in water) will last almost 24 hrs. Boiled(Cooked and refrigerated) will last 3-4 days.
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.
Spoon the potatoes into the serving dish, if you are serving the dish family style. Use the back of the spoon to smooth and round the pile of potatoes. If you are plating the potatoes in the kitchen, leave them in the mixing bowl or pot and cover the bowl with aluminum foil until you are ready to serve.
Put the lid on your mashed potato pot and gently place the pot inside the simmering water bath. Leave the stove on and allow the water to simmer for as long as you need it to keep your potatoes warm. Not only will the water bath keep your potatoes warm, but it will also keep them light and fluffy.
Make-ahead mashed potatoes are a great option for the holidays. You can do nearly everything — boil, peel, and mash; stir in milk and salt — up to two days ahead. Before serving, reheat. Adding butter at the last minute makes them taste freshly mashed.
The right amount of heat gives you smooth, creamy potatoes. But too much heat causes the starches to burst, and the potatoes to become gelatinous and gluey. Fighting these two potential outcomes is difficult when you make fresh mashed potatoes, but it's even more difficult when reheating leftovers.