Natural Casings

• Natural sausage casings are provided by the animal itself, in the form of intestines and other nooks and crannies found in the digestive system. The most common variety are hog intestines, which provide the wrapper for common sausages such as bratwurst or English-style "bangers." Larger and smaller casings are gleaned from hogs, cattle and even lambs, with each having its traditional uses. Natural casings, in general, are always edible. You can choose to eat them or not, depending on the sausage and your own personal preference.

Extruded Collagen

• Extruded collagen casings are easier for sausagemakers to work with, because unlike highly perishable natural casings -- which require brine and refrigeration -- extruded collagen casings are sold dry and can be kept on the shelf until they're needed. Collagen is a form of connective tissue that occurs naturally in meats, breaking down after long cooking to form the gelatin that gives pot roast or pulled pork its richness. To make sausage casings it's forced through a ring-shaped press, then dried and compressed accordion-style into a tightly crinkled cylinder. The collagen rehydrates and softens once the sausage is stuffed, and the casings are completely edible.

Artificial Casings

• One problem with natural casings is that in the larger sizes, animals tend to have only a modest length concealed in their anatomy. Those large sizes -- usually found in deli meats, and also on some coil-type sausages -- are often manufactured artificially for modern-day meatpackers. The casings are made from many materials, but are typically some form of foodsafe plastic. They protect the sausage with an airtight coating that keeps out bacteria and mold spores, but it's not meant to be cooked. This type of casing is always removed before the sausage is cooked or eaten.

Knowing What You've Got

• If you aren't an experienced cook or a sausage aficionado, it can sometimes be difficult to tell the various casings apart. Fresh sausages are relatively easy, because they're meant to be cooked and eaten with the casings in places. They use natural or extruded-collagen casings, which cook and brown beautifully. With larger sausages, you might need to remove a small piece of the casing to test it. If it's visibly plastic, or too tough to chew, it's unlikely that it was intended for eating. Remove and discard it in good conscience, before cooking the sausage.