Sausage casing is the material that contains and encloses the filling of a sausage. Casings are typically divided into two categories, natural and artificial.
Natural casings are made from the submucosa, a layer of the intestine that consists mainly of collagen. The fat and the inner mucosa lining are removed. Natural casings tend to be brittle once cooked and tend to "snap" when the sausage is bitten. They may also rupture during the cooking process; often, this indicates that the cooking was done too rapidly. Natural casings may be hardened and rendered less permeable through drying and smoking processes. Natural casings are generally made from porcine, bovine or ovine intestines.
Collagen casings are produced from the protein in beef or pig hides. They have been made for more than 50 years and their share of the market has been increasing. Continuous development means the casings are now preferred by consumers in many sausage applications. Usually the cost to produce sausages in collagen is significantly lower than making sausages in gut because of higher production speeds and lower labour requirements.
Artificial casings are made of cellulose or even plastic and may not be edible.