Pork spareribs contain eleven to thirteen ribs from the belly region. The breastbone may also be included and should be removed or notched.
The technique illustrated here is used when making Costine.
Place the slab of ribs on a board with the bone side up.
Place your boning knife flat against the rib bones. Remove the diaphragm, or skirt, by gripping the skirt meat and, as you lift up on it, cutting it as close as possible to the slab without cutting into or exposing the bones. (Removing the skirt ensures even thickness and therefore even cooking.)