Soak raw potatoes in water for several hours when they are left sitting out without any harmful effects, or soak them overnight as long as they are refrigerated. Soaking raw potatoes in water helps to remove amylose, which is the starch molecule responsible for giving mashed potatoes a paste-like texture. The potatoes must be cut into small, 1-inch pieces to remove a significant amount of the starch.
Washing potatoes that are parboiled or steamed helps to remove a greater amount of amylose than simply soaking them in water, creating mashed potatoes with a much fluffier texture. Rinsing is also beneficial for potatoes that are fried because the starch on the outside of the potatoes tends to burn before the inside of the potato is cooked.
Potatoes contain approximately 18 percent starch, although different kinds of potatoes contain different amounts. Russet and white potatoes have the highest starch content, so they do not hold their shape well after cooking. Their mealy texture is perfect for making mashed potatoes or for baking. Red and yellow potatoes have less starch which gives them a creamy texture that holds the potatoes' shape well after cooking. These potatoes work well for potato salad, soups and stew recipes.