Baking bags are a wonderful invention: They trap moist air, which speeds cooking and helps keep your roasts and holiday turkeys from drying as they cook. One thing they can't do, though, is make all the ingredients inside finish cooking at the same time. You could put long-cooking root vegetables in the same bag with a big pot roast, for example, but not with a smaller, quick-cooking cut of meat like pork tenderloin.
Root vegetables take significantly longer to cook than a pork tenderloin, so preparing them in the same baking bag is problematic.
A Pork Tenderloin Primer
While the much larger loin is cut from the thick muscle running along the top of the hog's ribs, the tenderloin is a much smaller cut – about the size of a slender forearm – taken from the underside of the ribs. They average 12 to 24 ounces in weight, just right for two to four entree portions. Tenderloin is a lean, boneless cut, so there's very little waste: All you need to do before cooking is remove a thin sheath of tough membrane, called silverskin, from the surface. Depending on the temperature you choose, it can be done in as little as 12 to 15 minutes in the oven. Putting pork tenderloin in an oven bag isn't necessary to speed its doneness, then, but putting a sauce or marinade into the bag is a convenient way to flavor the pork as it cooks.
Vegetables Take Longer
The problem with roasting vegetables in the same bag with your tenderloin is that root vegetables, including carrots and potatoes, typically take longer to cook at any given temperature than the pork will. That's not a deal-breaking problem, but it does mean you can't just dump everything into your bag and call it a day. Instead, you'll need to follow one of three strategies:
- Par-Cooking the Vegetables: Shortening the vegetables' cooking time by par-cooking them is one way to make this dish work. Boil, steam or microwave the potatoes and carrots until they're just beginning to soften. Then drain them carefully, and add them to the bag with your pork tenderloin and any seasonings.
- Starting the Vegetables First: Alternatively, place the vegetables into your bag first, with your choice of seasonings or sauce, and cook them for 10 to 15 minutes. Open the bag, taking care not to let the gust of escaping steam burn your hands, and add the pork tenderloin. Close the bag and return it to the oven until the pork is cooked and the vegetables are tender.
- Choose Different Vegetables: Carrots are relatively dense and take longer to cook than potatoes, squash, sweet potatoes and many other vegetables. You could substitute sweet potatoes or winter squash for the carrots, for example, and cut the vegetables into 1/4 inch dices to speed cooking.
Tenderloin and Doneness
Pork needs to reach a temperature of just 145F, the same as other meats, in order to be food-safe. At that temperature it will be moist and flavorful, with a hint of pink. If you're serving people who can't feel comfortable eating pink pork, you can take that internal temperature to as high as 160F. It won't be as juicy as a less-cooked tenderloin, but it won't be unpleasantly dry either, especially if it's served with a sauce or gravy.