"This is the traditional Puerto Rican holiday meal. My Grandma's recipe is unique because she marinates the meat in wine overnight. This pork roast is the most tender, flavorful meat you'll ever taste. You won't need a knife."
Crush garlic into small pieces in a mortar and pestle. Add olive oil, salt, oregano, and black pepper; mash into a paste.
Make 12 deep incisions a few inches apart in the roast using a sharp knife. Pack the seasoned garlic paste evenly into the incisions and over the roast.
Transfer roast to a large bowl. Pour in red wine, covering roast completely. Cover with plastic wrap and let marinate in the refrigerator, 24 hours.
Pour out red wine. Place roast fat-side up in a roasting pan; cover with aluminum foil. Let sit at room temperature, about 30 minutes.
Preheat oven to 400 degrees F (200 degrees C).
Place roast in the preheated oven; reduce temperature to 300 degrees F (150 degrees C). Bake until slightly pink in the center, about 4 hours.
Increase temperature to 400 degrees F (200 degrees C). Uncover roast and continue baking until fat is crispy and an instant-read thermometer inserted into the center reads 160 degrees F (71 degrees C), about 1 hour more.
Remove from oven and let rest before carving, 20 to 30 minutes.