Doing so is a science thing – soaking cut potatoes removes excess potato starch. This means fluffy mashed potatoes (and not gluey!)
Soak the potatoes in water for at least 4 hours, up to overnight. This step is crucial to really get all of the excess starch off. Fill a large pot with water, rinse off the potatoes one last time and add them to the cold water. Salt the water, place the pot on the stove and turn on the heat.
If you want to boil your potatoes in advance of mashing them, leave them sitting in about 1-2 inches of the cooking water for up to 2 hours. Then when it's time to mash them, you can bring the water to a simmer to reheat the potatoes.
Give them a cold water bath: Once your potatoes are chopped, toss them into a large bowl. Then cover the potatoes completely with cold water and let them soak for at least 30 minutes (or up to overnight). This will help to rinse off the excess starch and help the potatoes crisp up beautifully in the oven.
The reason is to prevent the potatoes exposure to air, which causes dehydration, oxidation, and discoloration. Immersing cut potatoes will also help rinse off excess starch.
Soaking potatoes in water helps remove excess starch. Excess starch can inhibit the potatoes from cooking evenly as well as creating a gummy or sticky texture on the outside of your potatoes.
Why use salt water for soaking potatoes? There's moisture naturally found in potatoes, and moisture is drawn to higher concentrations of salt. (This is a process called osmosis.) So, if you put the potatoes in a salt water bath, that will help draw out some of their moisture, resulting in crispier fries.
We usually recommend no more than 24 hours. You can keep the potatoes from absorbing the water by making sure the water is not salted, and is chilled (you can even add ice to the water). To keep the potatoes from turning black from oxidation, add 1 teaspoon of lemon juice or white wine vinegar to a gallon of water.
During cooking, heat makes the starch to swell in a process called gelatinization. This makes the potatoes to more likely to stick together. But proper soaking will prevent this to happen, resulting in potatoes that cook or fry much better— not sticky, but crispier. Just make sure potatoes are soaked in cold water.
Soaking peeled, washed, and cut fries in cold water overnight removes excess potato starch, which prevents fries from sticking together and helps achieve maximum crispness.
The Mistake: Overworking the Potatoes with a Food Processor, Blender or Mixer. Too much — or too vigorous — mashing will produce gluey potatoes. Your best tool is an old-fashioned masher, fork, ricer or food mill.
Tips for the Best Mashed Potatoes
Start cooking the potatoes in cold water: This ensures that the potatoes cook evenly. Otherwise, if you start with hot or boiling water, the outsides of the potatoes cook and soften while the middles are still hard and crunchy.
Cover the pot and simmer until potatoes are tender — about 15 to 20 minutes. A knife tip inserted into a potato should meet no resistance; if the potato clings to the knife, the potatoes need to cook longer. When potatoes are done, remove from heat and drain immediately.
A potato ricer is widely regarded as the best tool for mashed potatoes that are smooth and fluffy. Built like a big garlic press, it works by pushing cooked potatoes (one or two at a time) through a perforated grate, creating stringy, broken-down potato bits without releasing a ton of starch.
Rinsing potatoes helps remove excess starch, so it is recommended to rinse the potatoes before cooking. To ensure even more starch is out of the way, it's recommended that they even be quickly rinsed after boiling.
If you'll be cooking the potatoes in the next few hours, you can leave them submerged in water at room temperature, Tiess says. If it will be longer than a few hours, place them in the refrigerator.
Rinsing or soaking cut raw potatoes helps to wash away a very small amount of amylose. But the potatoes must be cut into one-inch pieces to expose enough surface area to wash away any significant amount of amylose.
Soak the uncooked potatoes for 30 minutes in an ice bath. They can soak longer, but you'll need to keep them in the fridge while they soak. Don't soak for longer than 3 hours.
Prepping the potatoes ahead of time
To save time on peeling and chopping on Thanksgiving Day (or any other day that includes mashed potatoes), you can peel the spuds and keep them submerged in a bowl of water in the fridge, whole or cut up, for hours — even overnight — before boiling.
Remove the potatoes from the soaking water, place them in a towel and squeeze out as much moisture as possible. Allow the water to rest for about 30 minutes so the starch settles. Pour the water out of the bowl, leaving the starch at the bottom of the bowl. Combine the starch and potatoes just before cooking.
They can sit for an hour, or two, like this, Foster says. When you are ready to continue, set the pot over low heat and the simmering water will heat the potatoes back up so you can mash them.
For most potato dishes it's important to add the potatoes to cold water and allow the water to come to a boil with the potatoes in the water. The potato starch can react as soon as it comes in contact with hot water, which will promote uneven cooking and mealy potatoes.
Potatoes soak up a lot of flavor, so salting the water prior to cooking is a good idea for the best taste. And you aren't limited to plain salted water for boiling your potatoes, either.
Add enough cold water to cover the tops of the potatoes. Add ½ to 1 teaspoon salt to the water. Turn the burner on high and bring water to boiling. Reduce the heat to medium-low or low.