Potato Science

Potato Varieties. Dennis Gottlieb/Photolab/Getty Images

Everybody loves potatoes; from french fries to twice-baked, Americans eat pounds of potatoes every year. There are many different types of potatoes, and each has a best cooking method.

Potatoes are all about starch and water; the cooking method controls the reaction between the two. As a high-starch potato is baked, the starch inside the potato absorbs water from other parts of the potato and swells, making a space between cells, creating a mealy, dry texture.

When a potato is deep fried, pan fried, or roasted, the starch on the surface expands, sealing the edges and the surface, creating a crisp crust and keeping the interior moist. Boiling, or low starch potatoes, do not absorb as much water, so the cell structure stays intact, and the potato holds its shape.

Potato Types

  • Russet potatoes have a high starch content with low moisture. These potatoes bake mealy and fluffy, and are the best choice for mashed potatoes and baked potatoes.
  • Medium starch potatoes include Yukon Gold and Yellow Finn potatoes. They aren't as fluffy as russet potatoes, but have great flavor. Yukon Gold potatoes, especially, taste buttery when cooked.
  • Potatoes with a low starch content and high moisture include red and white potatoes. These potatoes are most often boiled or roasted and used in potato salad because of their creamy texture. They hold together well after being cooked.
  • Sweet Potatoes and Yams are actually two different tubers. Yams are a member of the lily family, and sweet potatoes are members of the morning glory family. In the United States, you're almost always buying sweet potatoes; true yams are not very available. There are moist fleshed sweet potatoes and dry-fleshed potatoes. Both have lots of beta-carotene and potassium. They can be baked like russet potatoes, made into fries, or mashed. Sweet potato pie is another favorite recipe made from these tubers.

    For the best baked potatoes, long slow cooking is best. The skin becomes very crisp and turns darker because the starch just below the skin converts to sugar, which browns in heat. Make sure you cut a slit in the potato as soon as it comes out of the oven so the interior doesn't steam, which makes a heavier consistency.

    Twice baked potatoes are easy; they just require a little time. Bake the potato until tender, about an hour, then remove the flesh from the skins. Return the skins to the oven to keep them crisp while you make the filling. Then add the filling ingredients - cream, butter, cheese, seasonings - whatever you like; beat the filling, then refill the potato skins. Bake until the potatoes are beginning to brown and crisp.

    Mashed potatoes can be made from russets that are boiled or roasted. I myself prefer roasted, because I think it intensifies the potato flavor. The starch in the potatoes, once again, absorbs water and swells during the cooking process. Then when the potato is mashed or riced, the cells break open, releasing more starch, which makes the potatoes creamy and smooth. If you boil your potatoes for mashing, return them to the hot pan after draining and shake over medium heat for 2-3 minutes to dry the potatoes.

    Whatever the cooking method, add butter first when you begin mashing. That coats the cells and the starch so they absorb less liquid, making the potatoes less gluey and fluffier. For the actual mashing process, I prefer a potato ricer because it makes the smoothest mashed potatoes. Cook's Illustrated also prefers a ricer because it causes less damage to the cells.

    French fried potatoes are a bit more difficult to make at home. Frying them twice gives the best results. The potatoes must be dry when they are fried, or the starch will absorb the water on the surface and won't seal the potatoes so they will absorb grease. Greasy french fries are NOT desirable! Cut your fries from russet potatoes and place in a bowl of ice water as you work. This helps prevent the potatoes from changing color. Heat oil or vegetable shortening to 325 degrees.

    Dry the potatoes thoroughly in some paper towels. Cook the potatoes for 6-8 minutes until they become limp and just begin to change color. Remove from the fryer and let stand for 10 minutes. When you want to serve the fries, heat the oil to 350 degrees. Add the precooked potatoes and cook about 1-2 minutes until fries become golden brown and slightly puffy. Remove from the oil, salt, and serve! And here's a tip if you like to bake french fries: chill the potatoes in the refrigerator overnight the day before you want to make them. This changes some of the starches to sugar, which then makes the potatoes more brown, even in the lower, more indirect heat of the oven. I like to bake potatoes for French fries: see Amy's Potatoes for the recipe.

    Smashed potatoes are hot; they are simply small potatoes that are cooked until tender, then smashed with a drinking glass or potato masher. They are baked until crisp and golden on the outside and tender within. Any small or baby potato will work well cooked with this method.

    Hash brown potatoes are easy to make from scratch. Make sure you grate the potatoes just before cooking them, or else they will change color, turning pink or brown. This happens because the sugars in the potatoes oxidize, causing the color change. Russet or high starch potatoes are the best for hash browns. Grate them in a food processor or on a hand grater and dry thoroughly by squeezing in a kitchen towel. Season them to taste and cook in butter and olive oil, pressing the potatoes with a spatula as they cook. When golden brown on the underside, flip the potatoes and cook until dark golden brown.

    Roasted potatoes are simply cut into chunks and tossed with olive oil and seasonings, then baked at a high temperature, stirring once during cooking. I like to leave the skins on my roasted potatoes, but you can peel them if you like. These potatoes cook more like french fries, with the starch on the surface sealing the potatoes, making a crispy crust (even on cut sides) and a moist, tender interior.

    Bake potatoes at 400 degrees for 40-60 minutes until they are as brown and crispy as you like.

    Scalloped potatoes can be made with russets or low starch red potatoes. Russets will be more tender, and red potatoes will be firmer; the choice is yours! Slice potatoes 1/8" thick for the best texture and most even cooking, and try to get the slices the same thickness so they cook at the same time. Potatoes can be cooked in cream (see Potatoes Grand Mere) or in a thin white sauce, or for the easiest sauce of all, thinned condensed cream of mushroom soup.

    Potato Recipes