Mashed potatoes would seem to be the easiest thing in the world to make: just boil ’em and mash ’em, right? But potatoes are mostly starch, and a lot depends on how the starch behaves.
Potato flesh is made up of plant cells. Inside the cells are thousands of starch granules, little round packages in which the plant has stored the molecules of starch that it manufactured during photosynthesis. The starch inside the granules has a gelatinous consistency, so that the granules may be thought of as tiny sacks of glue.
When heated in a moist environment, the granules take on water and swell until some of the sacks disintegrate, spilling their gummy contents. The granules lose their grainy structure and become gelatinized.
But the game isn’t lost yet. If the spilled gelatinous starch remains trapped within the potato’s cells, your spuds are still okay because the potato’s cell structure keeps them firm. But if you then smash the cells open, the gooey starch runs out and gums up the works.
The best masher, in my opinion, is the type that has square or rectangular holes in a flat plate. It extrudes the potato through the holes as a ricer does, rather than crushing it.
When mashing, use an up-and-down motion; don’t slide the masher sideways, which would squash open more starch grains. That’s the trouble with those zigzag rod mashers; their round rods squish the potato sideways. And never use a food processor. It is notorious for making gluey potatoes because its sharp blades slash through the swollen starch grains, liberating lots of gluey gel.
Beyond all that, some potatoes are better for mashing than others. Small redskins are waxy and make a waxy mash. Best are the russets, or “Idaho baking potatoes,” and Yukon Golds, whose cell structures give a nice, mealy texture. And the color of the Yukon Golds makes your guests think there’s more butter in the mashed potatoes than there is.
How to make mashed potatoes:
Cut the potatoes into 1-inch pieces and precook for about 10 minutes at a simmer, not a full boil. That gives the starch grains a chance to swell without rupturing.
Then drain the potatoes and let them cool. That allows the swollen starch granules to firm up.
When you’re almost ready to mash, simmer the potatoes the rest of the way until they’re barely tender, not mushy.
Drain them very well and mash them with a potato masher or ricer. The firmed-up starch granules won’t release their goo as easily as they would have without the precooking and cooling steps.