Pressure cookers make short work of tough meat -- roasts and ribs succumb to the internal pressure created when water heats beyond its boiling point. Modern pressure cookers present few safety concerns -- their lids do not unlock and release until the pressure inside subsides to a safe level. A 5-quart pressure cooker handles two to three full racks of baby-back ribs with ease, but you can use a smaller vessel if you cut the ribs to fit and don't fill it more than two-thirds full. Pressure cooking takes ribs from tough to tender in well under an hour.
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Removing the Membrane
A thin cartilaginous membrane covers the underside, or bone side, of a baby back rack. This tough membrane causes the rack to curl during cooking, so you must remove it. Also trim away bits of fat dangling from the bones, as well as a shiny type of cartilage called silverskin, found on the meaty side of the rack.
Turn the ribs bone-side up on the work surface and slice away the loose fat using a paring knife. Next, flip the ribs over so they sit meat-side up. Work the tip of the knife under the silverskin and pull it away from the meat. Using a slicing motion while pulling the silverskin taut, separate it from the meat. You won't remove every sliver of silverskin, but get as much as you can.
Finally, turn the rack back over and work the tip of the knife under the tight membrane covering the bones. Release about an inch or two of the membrane -- enough to firmly grasp it. Using a paper towel to improve your grip, grasp the loosened portion of membrane and pull it from the ribs -- it should come off in a single piece.
Cutting to Fit
Prepping baby backs for the pressure cooker doesn't differ much from regular rib prep, but you may have to cut them down to size to fit. A full rack of baby backs contains between 10 and 13 bones and measures more than a foot and a half long.
If you have a full rack, cut it in half between the two center ribs to fit the cooker -- you need at least 1/2 inch of space between the end of the rack and the sides of the cooker.
Seasoning and Marinating
Marinades and dry rubs are viable options for ribs, and you can do both if you're feeling adventurous. Use a standard oil-based marinade to marinate: 1 part acid, 1 part oil, 2 parts aromatics and salt and sugar to taste. For example, a universal rib marinade might contain 1/2 cup of vegetable oil, 1/2 cup of soy sauce and 1 cup of herbs and spices.
Think of spice rubs as dry marinades -- like marinades, you need to apply them at least 12 hours before cooking to impart flavor below the surface of the meat. Dry rubs consist of four components: salt, pepper, transition spice and signature spice. Transition spices are typically mild and won't overpower the signature spices. Work with cumin, paprika, sage -- anything mildly aromatic. Signature spices add your touch to the ribs' flavor profile. A combination of garlic powder and chili powder and powdered mustard, for example, give the ribs an edgy note in the finish.
Apply the marinade or spice rub to the ribs, and set them aside in the refrigerator for at least 12 hours. If you want to add a dry rub after marinating, pat the ribs dry and apply the spices just before cooking.
Ribs -- all meats, for that matter -- need a strong sear before pressure cooking to brown and caramelize them. Pressure cooking, with all its benefits, won't brown foods -- it cooks with moist heat. Heat a couple of tablespoons of vegetable oil in the pressure cooker on the stove using medium-high heat. Next, sear the meat-side of the ribs until golden brown, then remove and set them the aside.
Place a cooking rack in the bottom of the pressure cooker -- the rack keeps the ribs from boiling in the cooking liquid. Add about 1 cup of chicken or beef stock -- pressure cookers need a minimal amount of liquid to create steam. Next, place the ribs on the cooking rack bone-side down in an even layer. You can stack the ribs, but don't fill the cooker by more than two-thirds. Cover the cooker, lock the lid and set the heat to high. When the cooker reaches high pressure, lower the heat to medium and cook the ribs for 30 minutes. Run cold water over the pressure cooker when finished and release the lock when it's safe to remove the cover.