To make sense of the many varieties, it’s helpful to group potatoes into three major categories based on texture. We recommend different potatoes for different gratins based upon how much starch we need them to contribute to the sauce and what kind of texture we want in the finished dish.
Floury potatoes contain more total starch (20 to 22 percent) than other varieties, giving them a drier texture. Because of that, these spuds are excellent candidates for baking and frying. They're also ideal for mashing because they can drink up the butter, cream, and whatever other flavorful liquids they come into contact with. They work well when you want to thicken a stew or soup, but not when you want distinct chunks of potatoes in the finished dish. Common varieties include russet, Russet Burbank, Idaho, and White Creamer.
These potatoes contain less total starch (18 to 20 percent) than baking potatoes, but more than boiling potatoes. Although they’re considered “in-between” potatoes, they’re technically closer in texture to the baking than the boiling variety, so they’re also a suitable choice for baking, frying, and mashing. In addition you can use them in salads and soups, but they won't be quite as firm as boiling potatoes. Common varieties include Yukon Gold, Yellow Finn, Purple Peruvian, Kennebec, and Katahdin.
These potatoes contain a relatively low amount of total starch (16 to 18 percent), giving them a firm, smooth, waxy texture and a higher moisture content than other varieties. They’re often called “new” potatoes because they’re harvested in late spring and summer and therefore less mature. Because they haven't had the long storage time to convert their sugars into starch, they’re less starchy than their “old” kin; they also have thinner skins. Boiling potatoes are perfect when you want the pieces to hold their shape, as with potato salad or when roasting wedges or chinks. Common varieties include Red Bliss, French Fingerling, Red Creamer, Red Pontiac, and White Rose.