Preheat an outdoor smoker or pellet grill to 250 degrees Fahrenheit (121 degrees Celsius).
Remove the membrane from the back of 1 rack pork ribs. Slide fingers under the membrane to loosen and peel off. Use a paper towel for grip if needed.
In a food-safe spray bottle, combine 1/2 cup apple juice and 1/2 cup apple cider vinegar. Set aside.
Spread 1/4 cup whole grain mustard evenly over both sides of the ribs to act as a binder.
In a small mixing bowl, combine 1 tablespoon smoked paprika, 2 teaspoons salt, 1 teaspoon black pepper, and 1 teaspoon garlic powder. Rub mixture evenly over the mustard-coated ribs.
Place ribs directly on the grill grate, meat side up. Spray ribs lightly with the apple juice and vinegar mixture. Close lid and cook for 5 to 6 hours. Spritz ribs every hour to keep moist and promote smoke flavor.
During the last hour of cooking, brush ribs with 1 cup barbecue sauce, if desired.
Ribs are done when they bend easily when lifted with tongs and the meat begins to pull away from the bone which should happen when they reach an internal temperature between 195 to 203 degrees Fahrenheit (90 to 95 degrees Celsius).
Notes
For a sweet and fruity smoke, go with fruitwood pellets like apple or cherry. If you’re after that classic Southern barbecue flavor, hickory pellets are the way to go.