Mix together brown sugar, paprika, smoked paprika, garlic powder, onion powder, and salt in a small bowl.
Remove the membrane from the ribs. At one end of the rack, slide a dinner knife under the membrane and over a bone then lift until the membrane loosens. Grab the edge of the membrane and pull it off--it may come off in several pieces.
Generously rub the spice blend over the entire surface of the ribs.
Place trivet in the pressure cooker. Pour in apple juice into the bottom of the inner pot. Add liquid smoke. Roll ribs in a circle and place on the trivet in the pressure cooker. Place lid on the pressure cooker and be sure the vent knob is pointed towards sealed.
Cook ribs on High Pressure. For Baby Back Ribs set cook time to 25 minutes. For Spare Ribs set cook time for 35 minutes. To set cook time, hit manual or pressure cook and use +/- buttons to adjust cook time.
Once cook time has elapsed, allow pressure to release naturally for at least 15 minutes.
Optional Step: Place cooked ribs on sheet/broiler pan. Brush with your favorite barbecue sauce. Broil under high heat for 3-4 minutes. Flip, brush with more BBQ sauce and broil for 3-4 minutes on other side.
Using an 8 Quart Instant Pot: Use 1 ½ cups apple juice for 8-quart pressure cookers, but leave the cooking time the same. Double the Recipe: Feel free to make 2 racks of ribs. Simply place both racks of ribs on the trivet and cook as directed (cook time does not change).Storage: Store leftover ribs in the refrigerator for up to 3 days. Reheat under the broiler for the best results.No Apple Juice? Water or stock can be used in place of the apple juice, but the apple juice adds an applewood flavor to the ribs.It is not necessary to add barbecue sauce to the ribs or to broil them but it does add another layer of flavor.See Instant Pot High Altitude Conversion if cooking 2500+ feet above sea level.