1. MAKE THE MOP Light a grill. In a large bowl, combine all of the
mop ingredients and whisk until smooth.
2. PREPARE THE RIBS Season the ribs all over with salt and pepper.
Layer two 18-inch sheets of foil on a work surface and set a half
rack of ribs in the center; pull the edges of foil up around the ribs.
Spoon 3/4 cup of the mop over the rack and seal tightly in the foil.
Repeat with the remaining 3 racks. Grill the rib packets over
moderate heat, covered, for 45 minutes. Using tongs, transfer the
rib packets to a baking sheet and let cool slightly.
3. Meanwhile, transfer the remaining mop to a medium
saucepan and bring to a boil. Simmer over moderately low heat,
stirring constantly, until reduced to 1 cup, 12 to 15 minutes;
let cool completely.
4. Wrap the wood chips in a double layer of foil and poke holes
in the top of the packet. Remove the grill grate. Turn the heat off
on half of the grill or rake the coals to one side. Set the wood chip
packet directly on the flames or on the coals and replace the
grill grate. When the chips are smoking, carefully open the rib
packets and arrange the racks on the grill over indirect heat.
Discard the foil and juices. Cover the grill and smoke the ribs until
the meat is very tender, 1 hour. Brush the ribs with the reduced
mop, transfer to a platter and serve.
MAKE AHEAD The finished ribs can be refrigerated for up to 2 days.