1 Prepare the brine: Combine the juices and water and measure in a measuring cup. You should have exactly 2 1/2 cups liquid. If you have less, add enough water so that you have 2 1/2 cups of liquid, if you have more, discard the excess. The correct ratio of liquid to salt is important for the brine to work properly.
Place liquids in a medium sized bowl, add other brine ingredients—salt, thyme, and red pepper flakes. Stir for half a minute until the salt has completely dissolved.
2 Prepare the ribs: If you want, remove the thin membrane that lines the concave side of each rib rack. This will make it easier for the brine and spices to penetrate as well as easier to cut and eat when the ribs are done. Insert a dull knife edge between the membrane and ribs to loosen. Grip the loosened membrane and pull away to remove.
Cut the racks in half. Put in a plastic ziplock freezer bag. Add the brine to the bag. Squeeze the excess air out of the bag and seal the bag. Massage the brine into the ribs. Place the bag of brine and ribs into a bowl (in case there is leakage) and place into the refrigerator.
Refrigerate in the brine for 3-6 hours. Note that brining too long can over-saturate the meat with the brine. So stick within the 3-6 hour time frame.
3 Prepare bourbon glaze: Heat bourbon with sugar, peppers, and salt. Whisk in butter until melted. Set aside or refrigerate for up to 2 weeks. Warm before using. You can also prepare while the meat is cooking in the next step.
4 Prepare the grill for indirect heat: On a gas grill, heat the grill to medium heat 300-325°F with the middle burners turned off (if a 3 or 4 burner grill) or one burner turned off (if a 2 burner grill).
For a kettle grill with charcoal, use 3-4 pounds of briquets pushed to one side of the grill. An aluminum disposable drip pan set next to the briquets, underneath where the meat will be, will help keep your grill easier to clean. (I forgot this time, notice no drip pan in the photo, and now the grill's a mess.)
5 Place ribs on grill, adjust vents, maintain low heat: Remove the ribs from the brining bag. Pat dry the ribs with paper towels. Brush grill grates with olive oil or canola oil. Place the ribs on the side of the grill away from the source of heat, either gas or briquets. Cover the grill.
If you are using a gas grill, lower the burners so that you are maintaining a temperature of about 300°F-325°F in the grill.
If you are charcoal grilling, cover the grill so that the air vent on the kettle top is directly over the ribs. This way smoke from the charcoal will waft its way over the ribs on the way out of the grill.
Adjust the vents so that the air flow is much reduced. Reducing the size of the air vents is a way to help control the temperature in the grill and keep it low. Fire lives off of oxygen, so if you reduce the oxygen, you reduce the amount of burning and heat. If you close the vents too much, the charcoals will put out too little heat, so the trick is to maintain a balance - enough air flow to keep the coals alive, but not too much or the grill will run too hot and your ribs will overcook.
Try to maintain a temperature of about 300°F-325°F in the grill. If you are using a charcoal grill that doesn't have a built-in thermometer, you can put a meat thermometer through the grill air vent to take a reading of the temp.
6 Flip ribs over, check for doneness: After 20-25 minutes of cooking, use tongs to flip the rib racks over. If you are charcoal grilling, shift the ends of the ribs as well so that the end that was facing the coals now faces the edge of the grill.
Check for doneness using a meat thermometer after 15-20 more minutes. They are done and ready to pull off at 155°F, but you want to get to them 10 minutes or so before they are done to apply the glaze.
7 Apply bourbon glaze: At about 145°F start applying the spicy bourbon glaze. Brush the ribs with the glaze syrup, turning and basting the ribs until the syrup has been used up. When an instant read thermometer, inserted into the thickest part of the ribs reads 155°F, the ribs are ready to take off the grill.
Note that depending on the amount of heat in the grill and the size of your ribs, the ribs could be done in as little as 45 minutes or as long as 1 1/2 hours. If the grill temperature stays more at about 350°F, then the ribs will be done faster. It's hard to maintain a charcoal grill lower than 350°F, though ideally for these ribs you do want the temp lower, closer to 300°F. Also note again that baby backs are smaller than St. Louis style and will cook faster.
8 Remove the ribs to a large serving platter and cut into 1 or 2-rib sections.