One of the starch molecules in potatoes is called amylose, which is responsible for making mashed potatoes "gluey" and pasty. 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. It's not worth the trouble.
Washing parboiled or steamed potato pieces removes much more amylose and is worth the trouble. The result is very fluffy mashed potatoes.
(If you decide to try soaking the raw potatoes anyway, they can be soaked in water in the refrigerator for several hours without any safety concerns. Potatoes can be soaked even overnight as long as they are in the refrigerator.)
Guy Crosby is the science editor for America’s Test Kitchen and an adjunct associate professor in the department of nutrition at the Harvard School of Public Health.
