Prepare a grill for medium-high heat; lightly oil grates. Remove ribs from foil (if desired, stir cooking liquid into sauce) and cut racks in half crosswise. Place ribs on grill, meaty side down, and grill until lightly charred, about 1 minute. Brush ribs with sauce and turn over. Brush with more sauce and continue to grill, turning ribs one or two more times, until sauce is lightly charred in spots, about 2 minutes. Transfer to a cutting board and let rest 5 minutes before slicing into individual ribs.