1Remove the thin, papery membrane from the back of each rack of ribs: Turn a rack meat side down. Insert a sharp implement, such as the tip of a meat thermometer, under the membrane (the best place to start is right next to the first rib bone). Using a dishcloth or pliers to gain a secure grip, pull off the membrane. Repeat with the remaining racks.
2Place the ribs in a large non-reactive roasting pan. Pour the 1-quart of pineapple juice over them and add the cilantro and jalapenos. Let the ribs marinate in the refrigerator, covered, for 2 to 3 hours.
3Make the glaze: Place the 2 cups pineapple juice, the vinegar, brown sugar, butter, and black pepper in a heavy saucepan over high heat and bring to a boil. Let the glaze boil until syrupy and reduced to about 1 cup, 10 to 15 minutes, stirring occasionally with a wooden spoon. Set the glaze aside.
4Drain the marinade off the ribs and discard the marinade. Blot the ribs dry with paper towels, then sprinkle the jerk seasoning all over them on both sides, patting it onto the meat with your fingertips.
5Set up the grill for indirect grilling and preheat to medium. If using a charcoal grill, place a large drip pan in the center.
6When ready to cook, place the ribs, preferably on a rib rack, in the center of the hot grate, over the drip pan and away from the heat. Cover the grill and cook the ribs until tender, 1 1/4 to 1 1/2 hours. When the ribs are done, they’ll be handsomely browned and the meat will have shrunk back about 1/4 inch from the ends of the bones. After 45 minutes brush the ribs with the glaze and brush them 2 or 3 more times before serving. If using a charcoal grill, after 1 hour you’ll need to add 12 fresh coals to each side.
7Transfer the cooked ribs to a platter or cutting board. Serve them as whole racks cut the racks into pieces, or carve them into individual ribs. Serve the glaze alongside.