If the pork tenderloin hasn’t been trimmed, it’s important to do this as part of your preparation. The tenderloin has a tough membrane, known as the silver skin, that is non-dissolvable, meaning it won't break down—even with cooking. This can result in tough and chewy meat. You can remove the silver skin with a sharp knife or buy trimmed pork tenderloin instead (most tenderloins are sold with the membrane already trimmed).