The membrane is a thick piece of plastic-like skin found on Pork baby back and spare ribs, as well as on beef back ribs. If not removed, it will prevent smoke and flavorings from penetrating the meat, which will greatly diminish the eating experience. You can easily remove the membrane by inserting a knife or other sharp object under one corner and prying it up. Then, use a paper towel to grip the membrane and pull it completely off. If it tears, just pry it up again and repeat the same process until all of the membrane is removed.