Place ribs in a 1-gallon sealable plastic bag set in a shallow dish. For the marinade, stir together the stout, onion, honey mustard, garlic, and caraway seed. Pour the marinade over ribs. Close the bag. Marinade ribs in the refrigerator for 6 to 24 hours, turning bag occasionally.
Drain the ribs, reserving marinade. Sprinkle ribs with salt and pepper. Pour marinade into a small saucepan. Bring to boiling; reduce heat. Simmer, uncovered about 15 minutes or until the marinade is reduced by about half.
Meanwhile, prepare grill for indirect grilling. Test for medium heat above the drip pan. Place ribs, bone side down, on the lightly oiled grill rack over the drip pan. Cover and grill for 45 to 55 minutes or until juices run clear, brushing ribs frequently with marinade during the last 10 minutes of grilling. Discard any remaining marinade. Garnish with fresh sage leaves and serve with grilled sweet onion wedges, if desired. Makes 4 servings.