Many recipes contain instructions that aren't fully explained in the accompanying text or might be omitted from similar recipes in other cookbooks. For novice cooks and bakers, it's often unclear which instructions have a clear and unequivocal benefit -- and which are just traditional and customary. For example, most instructions for baked potatoes advise the cook to poke several holes in it with a fork before it goes into the oven. That might seem like an ineffectual gesture, but it actually serves an important purpose.
The potatoes most often used for baking are large russet-type potatoes, often weighing a pound each in steakhouses and roughly half that at home. They're a type of potato referred to in cookbooks as mealy or floury potatoes, as opposed to firm-fleshed waxy types such as Yukon Gold. The type of starches found in russets cook up to a dry and fluffy texture, ideal for playing host to butter, sour cream, cheese and all the other moist, rich toppings diners love on their potatoes. Piercing the potatoes helps you achieve that classically dry, fluffy texture.
Every potato contains a high volume of water. Just think about how a tiny package of dehydrated potatoes fills your casserole dish after baking, or how large a portion of instant mashed you get from a small cup of flakes. When you bake your big russets, much of that moisture is turned to steam by the oven's heat. Steam takes up a lot more space than water, and as it builds up it creates a great deal of pressure inside the potato. If you don't give the steam a way to escape, your potato can split or even explode dramatically, showering your oven with potato fluff.
That need for steam to escape is exactly why most recipes advise you to poke lots of holes in the potato. The fork's tines create narrow vents, where the steam can make its escape from the potato. A few shallow, desultory stabs with the fork often won't do the job. Push the fork in far enough to provide venting right to the center of the potato, where much of the steam originates. Use a skewer or paring knife, if the potatoes are too large for your fork. Make sure to perforate the potato on all sides, leaving no area without venting.
Much of the flavor of a baked potato comes from the crisping and browning of the skin in your oven's heat, much as the flavor of toast comes from the browning effect of the toaster. Generating those flavors requires high temperatures, but if your potato bakes in too hot an oven, it's likelier to burst and might become overcooked. The Idaho Potato Commission, after extensive testing, concluded that potatoes baked best at 400 degrees Fahrenheit for approximately an hour. They should finish with an internal temperature of 205 F to 210 F, if tested with an instant-read thermometer.
- On Food and Cooking: The Science and Lore of the Kitchen; Harold McGee
- Idaho Potato Commission: How Do You Cook a Baked Potato?
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