Place each rack of ribs on a large sheet of aluminum foil. Divide the garlic powder between the racks, sprinkling it evenly over the surface. Squeeze the juice from the lemon wedges over the racks and season them all with salt and pepper. Toss the lemon wedges and apple juice over each rack of ribs and enclose each in the foil to seal. Marinate the ribs for at least 4 and up to 24 hours.
Preheat an oven to 250ºF.
Place the racks onto a baking sheet and pop them into the oven. Roast for 2 hours, until the meat is tender and pulls away from the bone.