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.
Use 1 1/2 cups apple juice for 8 quart pressure cookers.
The liquid smoke is optional, but helps to give these ribs a smoky flavor.
Water or stock can be used in place of the apple juice, but the apple juice adds an applewood flavor to the ribs.
Feel free to make 2 racks of ribs. Simply place both racks of ribs on trivet and cook as directed (cook time does not change).
It is not necessary to add barbecue sauce to the ribs, but does add another layer of flavor to these instant pot ribs.