I have always roasted my turkeys in a 325-degree oven for 12 to 15 minutes per pound. But lately, I've been seeing recipes for very high-temperature roasting -- 450 or 475 degrees. What, if any, is the advantage to this?

In all cooking, after all the shopping and schlepping and chopping and prepping are done, there are two decisions a cook has to make: how long to cook the food, and at what temperature.

Intuition suggests that these two variables, time and temperature, are inversely related -- that is, that a short time at a high temperature should somehow be equivalent to a longer time at a lower temperature. That's true, but unfortunately, it's not a direct tradeoff, such as, for example, 20 minutes less cooking time for each 10-degree increase in temperature. Having selected a temperature, we still have to make an educated guess as to when the food will be done. That goes for virtually all cooking methods, from simmering to grilling.

In the case of simmering or braising, we have no choice of temperature; we're limited to approximately 212 degrees, the boiling point of water. We can't get the food hotter than that, so we must generally simmer it for a relatively long time. We then determine when the food is done, not by its temperature, which does not increase as the cooking progresses, but by its degree of tenderness.

On the other hand, in dry cooking, such as -- oh, just to pick a random example -- roasting a turkey, we can in principle choose any cooking temperature from approximately 200 to 450 degrees. (My electric oven can be set at anywhere from 170 to 550 degrees.) Traditional roast turkey recipes have settled on a moderate 325-degree oven for about 20 minutes per pound. To determine when the turkey is done, check its internal temperature.

Of late, some surprisingly high-temperature roasting recipes have been popping up, specifying oven settings as high as 475 degrees, with roasting times as short as two hours. Startling as they may seem, these methods are based on sound principles. Nor are they new. Barbara Kafka, in her 1995 book, "Roasting: A Simple Art," pioneered the roasting of everything from beef, pork and lamb to vegetables, fish and, yes, chickens and turkeys -- all at the same temperature of 500 degrees.

One's first fear might be that at such high temperatures the turkey will burn. But burning is just an extreme stage of cooking, subject to the same time vs. temperature tradeoff as any other. That is, the high temperature is offset by the short time, and burning doesn't occur. Another example: A chef can taste a simmering sauce by dipping a finger into it so briefly that there is no time for the finger to be heated to a painful temperature. Conducted heat travels slowly.

The big question is, "When is the turkey at the best eating stage?" As with any meat, the most reliable way of determining doneness is to measure the internal temperature. That's because when proteins are cooked, their curly molecules unravel and bond together in new, less rigid ways, making the meat more tender.

But if the temperature rises too far, the protein tightens up and squeezes out water. That's why overcooked meat can be tough and dry. So the trick is to stop cooking when the meat reaches just the right tenderness and juiciness.

But what is that optimum temperature? There's the rub. And where do you take a turkey's temperature, anyhow? There can be differences of as much as 20 degrees between different parts, because heat travels slowly from the very hot outer parts to the less hot inner parts.

The traditionally recommended place to measure a turkey's temperature is in the thickest part of the thigh. That's likely to be the meaty part farthest from the bird's surface and therefore the last to reach a given temperature by heat conduction from the outside.

The U.S. Department of Agriculture, adopting the worst-case scenario that your turkey is riddled throughout with germs, recommends that that temperature be 180 degrees, thereby guaranteeing that all other parts will be even hotter. Less fretful recipe writers often suggest substantially lower temperatures.

The advantages of high-temperature roasting? For one thing, the turkey's skin is reputed to get nice and crisp, especially if it had been rubbed with olive oil or butter before being put in the oven. Also, the high temperature can mean a roasting time of as little as two hours for an unstuffed, untrussed bird. Leaving the cavity open and the legs akimbo allows the hot air to enter and cook the meat from the inside as well as from the outside. That is an essential part of the high-temperature roasting method.

Robert L. Wolke (www.robertwolke.com) is professor emeritus of chemistry at the University of Pittsburgh. His latest book is "What Einstein Told His Cook 2, the Sequel: Further Adventures in Kitchen Science" (W.W. Norton, 2005). He can be reached at wolke@pitt.edu.