Traditional natural hot dog casing is made from the small intestines of sheep.
Natural casing is a cleaned animal-intestine membrane used to contain sausage during filling and cooking. Sheep casings are especially associated with hot dogs and frankfurters because they are relatively narrow, producing the familiar slim shape. The casing remains on the sausage and contributes a firm texture and the characteristic “snap” when bitten.
This is different from the sausage filling, which may contain pork, beef, chicken, turkey, or combinations of meats. The casing’s animal source does not determine the meat inside. Kosher hot dogs generally avoid traditional animal casings, so they are often sold skinless or made with collagen casings.
Pigs and cattle are also important sources of sausage casings, but they are not the traditional answer for the narrow natural casing associated with hot dogs. Many supermarket hot dogs are skinless, meaning their temporary casing is removed before packaging.