Pork loin may be purchased pre-marinated or plain. If you enjoy the flavors that manufacturers provide, by all means, save some of the work!
Otherwise, buy a lean loin and marinade it in a little olive oil, a dash of lemon juice and herbs and spices to taste. Allow to marinate at least an hour, overnight is even better.
Step2
Preheat oven to 325, or temperature indicated on wrapper. Place entire loin on a grate, and place in roasting pan. Bake for 30 minutes per pound of meat.
Step3
After initial cook time has completed, insert a meat thermometer into the center of the loin. If the thermometer does not read at least 160 degrees, your loin is not fully cooked. Continue to bake until internal temperature is reached, checking every 15 minutes or so.
Step4
Allow meat to sit at least 10 minutes after removing from the oven. Meat that is sliced immediately will be very dry, time is needed for the juices to redistribute.
Step5
Slice as preferred. If not serving the entire loin immediately, only cut what is needed for that meal. The pork will maintain considerably more moisture if left intact, for leftovers.
Tips & Warnings
Cranberries, yams, any chutney or sweet relish is a delightful accompaniment to pork.
Slice the leftover loin very thinly and use for sandwiches or wraps.
Dice and add to soups or stews.
Try a loin on the grill, with mesquite chips. Wonderful!
Always be sure to bake to correct internal temperature. Undercooked pork has several health issues associated with it, most quite unpleasant!
Enthusiast 
