We Prove It: Hot Food Keeps Cooking

Recipes engineered for perfection—what exactly does that mean? We take you inside Cook’s Illustrated’s science experiments.

You buy an expensive roast and monitor it carefully as it cooks. When the temperature in its center reaches 130 degrees—the standard published temperature for medium-rare beef—you take the roast out of the oven and let it rest. Five, 10, 15 minutes. After 20 minutes you begin to slice, only to find that the roast is a dull shade of gray and no longer pink at all. In fact, it appears to be cooked to medium, not medium-rare. What happened?

THE BACKSTORY

As a roast rests, its hotter exterior will transfer heat to the cooler center and equalize the meat’s temperature. This phenomenon is called carry-over cooking. The thicker the cut of meat and the higher the cooking temperature, the more the temperature of the meat will continue to rise—anywhere from 10 to 15 degrees over the course of 15 to 30 minutes. Thus, steaks and roasts should be taken off heat well below the desired degree of doneness.

Left: In the oven, heat is hitting the exterior of the meat and moving by conduction toward the center. Right: At rest (out of the oven), heat is rapidly exiting from the hot exterior but continuing to move toward the center, cooking the meat even further.

THE EXPERIMENT

To demonstrate the effects of carryover cooking, we roasted four pork loins, varying both the internal temperature at which they were removed from the oven and the time allotted for carryover cooking. Two roasts were cooked until their internal temperature reached 140 degrees; we sliced one roast right away and let the other roast rest for 15 minutes before slicing, sticking a thermometer probe in its center so we could track its internal temperature during the resting period. The other two roasts were cooked to an internal temperature of 150 degrees; we sliced one of these roasts right away and let the other roast rest for 15 minutes before slicing, tracking its internal temperature as it rested as well.

The results were telling. The roast that was cooked to 140 degrees and then sliced right away lost significantly more juice than the roast that was rested for 15 minutes. We also noted that the roast sliced right away was very pink—in fact, it seemed underdone. In contrast, the roast that rested for 15 minutes was perfectly cooked with just a faint tinge of pink. The temperature of this roast had risen to 150 degrees during the resting period, and those 10 degrees made a big difference.

The results were similar for the two roasts cooked to 150 degrees. The roast sliced right away seemed perfectly cooked but we lost a lot of juice to the carving board.

When it comes to red meat, judging doneness, even with a thermometer, involves some guesswork. That’s because you aren’t judging whether the food is ready to eat, but whether it will be ready to eat once it has rested. That’s why we’ve put together the following guidelines, which includes the temperatures at which you should remove the roast to achieve your ideal doneness.

If you want: Rare beef or lamb
Stop cooking when temperature reaches: 115° to 120°
So final serving temperature is: 125°

If you want: Medium-rare beef or lamb
Stop cooking when temperature reaches: 120° to 125°
So final serving temperature is: 130°

If you want: Medium beef or lamb
Stop cooking when temperature reaches: 130° to 135°
So final serving temperature is: 140°

If you want: Well-done beef or lamb
Stop cooking when temperature reaches: 150° to 155°
So final serving temperature is: 160°

If you want: Medium pork
Stop cooking when temperature reaches: 140° to 145°
So final serving temperature is: 150°

If you want: Well-done pork
Stop cooking when temperature reaches: 150° to 155°
So final serving temperature is: 160°

This experiment is one of many included in our new book, The Science of Good Cooking by the editors of Cook’s Illustrated.

MAKE IT NOW: Our recipe for Maple-Glazed Pork Tenderloin is free through January 2, 2013.