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Casing (sausage), a thin covering holding the food contents of sausage. Casing or 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 or ovine intestine, though beef intestine may also be used.

Artificial casings are made of collagen, cellulose or even plastic and may not be edible.