Soak the wood chips in water for about 1 hour.

Slide the blade of a dinner knife under the thin, translucent silverskin that covers the bone side of each rack (note that some racks are sold with the silverskin already removed). Lift and loosen the membrane until you can grab it with a paper towel; pull it off and discard.

In a small bowl mix the spice rub ingredients. Sprinkle the rub all over the ribs, seasoning the meaty sides a little more than the bone sides and working the rub into the meat. Stand the ribs upright in a rib rack so that the meaty sides face the same direction. Leave as much room as possible between the racks; they shouldn't touch. Let the racks sit at room temperature for 30 to 60 minutes while you prepare the grill.

Drain the wood chips.

If your grill has a smoker box, follow the manufacturer's instructions for lighting the wood chips and heat one of the grill's burners on high (for indirect heat). If your grill doesn't have a smoker box, lay the chips evenly inside a small disposable aluminum drip pan. Cover the pan with foil. Poke 10 to 15 holes in the foil. Remove the cooking grate from the grill. With the lid open, light the grill with all burners on high. Close the lid and heat the grill for 10 to 15 minutes.

Using tongs or an insulated mitt, set the pan of wood chips in one of the rear corners of the grill, right over a lit burner or two (or over the steel bars covering the burners). Replace the cooking grate. Close the lid and wait until smoke pours out of the chip pan, usually 20 to 30 minutes. Then turn off all the burners except the one just below the chips

Carefully set the rib rack on the side of the cooking grate opposite the lit burner, with the bone sides of the racks facing the lit burner. (The bones will protect the meat from cooking too quickly.) Close the lid and adjust the remaining burner until the temperature is 300°F--this could require a low, medium, or high setting, depending on your grill. Smoke the ribs for 1 hour for baby backs, 2 hours for spareribs. During this initial cooking, prepare the mop and sauce.

Remove the ribs from the grill and from the rib rack and lay them on a large rimmed baking sheet. Lightly brush the ribs on both sides with about half of the mop. Carefully put the ribs back in the rib rack, again all facing the same direction but this time turned upside down so that the parts that haven't browned as much will get more exposure to the heat and smoke. Return the rib rack to the cool side of the grill, again facing the bone sides toward the heat. Close the lid.

Let the ribs cook until the meat shrinks 1/4 to 1/2 inch from the ends of at least several bones, 2 to 3 hours longer, and then check them for doneness (see below). During this time, baste the ribs occasionally with the remaining mop (don't bother removing them first from the rib rack). You may not use all the mop.

When the rib meat has shrunk 1/4 to 1/2 inch from the ends of several bones, lift each rib rack one at a time from the metal rack, holding the meat at one end with tongs. Turn the ribs bone side up and let them hang so that the weight of the other end bends the rack in an arc. If the meat separates and tears easily near the middle of the arc (see photo), that rack is fully cooked. Some racks take longer than others, as long as 4 hours total cooking time for baby backs and 5 hours for spareribs.

As each rack of ribs is fully cooked, lay it on a large sheet of heavy-duty aluminum foil. Lightly brush the ribs on both sides with the sauce--you may not need it all. Then wrap each rack individually in the foil. Let them sit at room temperature for 15 to 30 minutes for baby backs and 30 to 45 minutes for spareribs. Unwrap the racks, cut them into individual ribs, and serve warm.

Cook the bacon in a medium skillet over medium-low heat until browned and crisp, 10 to 15 minutes, turning occasionally. Drain the bacon on paper towels and eat it whenever you like. Pour about one-half the bacon fat into a small saucepan and reserve the remaining fat in the skillet for the barbecue sauce. To the saucepan, add 1/2 cup of the apple juice and 2 tablespoons of the cider vinegar. Bring to a simmer over medium heat and then remove from the heat (this is the mop).

Add the remaining 1/4 cup apple juice, 3 tablespoons cider vinegar, and the ketchup, Worcestershire sauce, chile powder, paprika, cumin, celery seed, and pepper to the bacon fat in the skillet. Cook over medium-low heat, whisking until smooth. As soon as the barbecue sauce simmers, remove the skillet from the heat.