Rinse the pork tenderloin and pat dry with a paper towel. Remove fat. Make several shallow crosswise cuts in the meat.
In a mortar, combine cumin, nutmeg, oregano, chili powder, and white pepper. Grind to release flavors and mix spices. Rub the meat with the spice mixture, place it in a deep glass or ceramic casserole dish, and set aside.
To make marinade, in a blender combine green chiles, malt vinegar, olive oil, guava nectar, pineapple juice, garlic and salt. Pour mix over pork and marinate at room temperature for one hour.
Preheat oven to 350 degrees F. Coat pork with marinade and bake for two hours.
Remove and let cool in juices. Remove pork to a large cutting board and pat dry. Pour off juices (or reserve for other uses such as gravy). With a fork, shred meat finely. Place shredded pork in a casserole dish and return to oven. Bake at 350 degrees F for 20 to 30 minutes or until crisp on top.
Carne de puerco is used as a filling for tacos, enchiladas, or any recipe that calls for shredded meat.