A pork loin roast is a tender, juicy main course, as long as you can keep it from drying out in the oven. To create a rich, caramel-hued crust on the surface of the pork, you must cook it with high heat. But, to keep the center of the loin moist and tender, the pork must slow-roast to preserve its natural juices. The key to preparing a sublime pork loin is adjusting the heat as the meat roasts, which allows you to achieve both qualities.
Soak the pork loin in a marinade, or coat it in a dry rub to flavor the meat. Dry rubs typically impart stronger flavors than marinades, since you are pressing the seasoning directly into the surface of the meat. Cover the pork with the lid to the container you marinate it in or plastic wrap to protect the meat from contamination.
Rest the pork loin at room temperature for 1 to 2 hours. The marinade or dry rub needs time to flavor the surface of the pork. Also, room temperature pork browns more effectively than cold pork because it rises to the temperature at which meat browns -- 310 degrees Fahrenheit -- more quickly.
Put the pork in a roasting pan, along with any vegetables or fruits you are roasting with the pork.
Place the pan in an oven preheated to 450 F. The high temperature browns the meat quickly, but it also results in quicker moisture loss. Reduce the temperature to 300 F once the surface of the pork loin is brown, after approximately 10 minutes. Slow-roasting the pork preserves its moisture more effectively. Cover the pork with aluminum foil when you reduce the temperature.
Check the internal temperature of the pork loin with a meat thermometer after approximately 20 minutes. To be safe to consume, the pork must cook until it reaches 145 F in the center of the thickest section, according to USDA guidelines. Many cooks recommend removing the pork loin from the oven when it is 5 to 10 degrees below the desired internal temperature, since the meat continues cooking for several minutes after you remove it from the oven.
Remove the pork loin from the oven once it reaches the desired temperature. Cover it with foil and let it rest for approximately 10 minutes. As the pork rests and cools, it becomes firmer, which improves juice retention. Cutting into the meat too soon will cause the juices in the center to spill onto the plate, which results in a loss of flavor. If you remove the pork loin early, insert the meat thermometer and leave it in while the pork rests, to ensure that the internal temperature has reached 145 F.