Recipes engineered for perfection—what exactly does that mean? The Science series takes you inside the experiments behind 50 cooking concepts featured in our new book, The Science of Good Cooking, by the editors of Cook’s Illustrated.
So it’s a special occasion, and you’ve cooked a maple-glazed pork loin for guests. It’s a beautiful piece of meat—thick and bronzed. Your kitchen is filled with a roast-rich, autumn-sugar scent that promises a great meal. We’ve all had the impulse to slice and serve a roast the second it exits the oven. But if you cut into that loin without a solid period of rest time, all the meat’s flavorful juice will rapidly run out onto the cutting board, leaving you with a dry, leathery dinner and some disappointed guests.
Resist the urge to slice. Resting is an indispensable technique when it comes to maintaining maximum juiciness. Here’s why.
Meat is mostly water. This water is trapped among the proteins that (along with some fat) make up the rest of the meat. This is why raw pork, for example, will not shed liquid when you cut it up. But cooked meat is a whole different story.
To back up: As we wrote in our blog post about burgers, the muscle tissue in raw meat is similar to many bundles of wire, each surrounded by a covering of connective tissue. Each wire represents a single muscle fiber. And each fiber is made up of protein molecules. When meat is heated, these protein molecules begin to compress and contract. A single muscle fiber can shrink to as little as half of its original volume during the cooking process. And when these muscle fibers contract, they squeeze out some of the liquid previously trapped within. If you slice your loin right after cooking, when the proteins are at their smallest, all that juice will come pouring out.
But the contraction of the muscle fibers is at least partly reversible. If you allow cooked meat to rest, the proteins will relax, allowing some of the expelled moisture to move back in.
That’s all great in theory. But when writing the chapter on resting meat in The Science of Good Cooking, Associate Editor Dan Souza, who was in charge of the test kitchen experiments, needed to figure out a way to demonstrate how much of a difference a little time on the cutting board could actually make when cooking a roast. He began with a handful of cutting boards and a whole lot of pork.
First, Dan roasted five boneless pork loins, each weighing about 3.7 pounds, in a 400-degree oven. He cooked them until their internal temperature reached 140 degrees.
One loin he sliced immediately into ½-inch-thick slices.
The others he tented with foil and let rest for 10, 20, 30, and 40 minutes, respectively.
He then collected all the juices.
And what did he find?
The roast cut immediately after cooking shed 10 tablespoons of liquid, both on the cutting board and on the serving platter. As you can see, that’s a lot of flavorful juice lost.
But what a different a few minutes makes: The roast that sat for 10 minutes lost just 4 tablespoons. That’s a 60 percent decrease in moisture loss.
And it only gets better: The roasts that rested for 20, 30, and 40 minutes lost 2½ tablespoons, 1 tablespoon, and 2 teaspoons of juice, respectively.
We had our tasters dig in. Not surprisingly, they described the roast that rested for at least 10 minutes to be juicier and more tender while the roast sliced without resting was drier and tougher. There wasn’t a whole lot of difference between the roasts that rested for 30 and 40 minutes.
So what to do? Curb your enthusiasm and let your meat rest. But not for too long. The most dramatic decrease in moisture loss for these pork loins took place during the first 10 minutes of rest. Additional time helps—but not if that means your dinner will be cold. If you’re cooking a big roast, you can wait longer—about 30 minutes. Thin steaks should only wait 5 to 10 minutes before you dig in.
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Our recipe for Maple-Glazed Pork Roast is free through October 22, 2012.
Got any juicy meat questions? Leave 'em in the comments.