Casing (sausage)

Casing or sausage casing is the material that contains and encloses the filling of a sausage

Sausage

A sausage is a prepared food, usually made from ground meat , ground pork fat such as fatback, salt, and spices . Typically the sausage is formed in a casing. Traditionally, sausage casings are made of animal intestines, though now some casings are synthetic...

. Casings are typically divided into two categories, natural and artificial.

Natural casings are made from the submucosa

Submucosa

In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle ....

, a layer of the intestine

Intestine

In anatomy, the intestine is the segment of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...

 that consists mainly of collagen

Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...

. The fat

Fat

Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition...

 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

Drying (food)

Drying is a method of food preservation that works by removing water from the food, which prevents the growth of microorganisms and decay. Drying food using the sun and wind to prevent spoilage has been known since ancient times...

 and smoking processes. Natural casings are generally made from porcine

Pig

Pigs are a genus of even-toed ungulates within the family Suidae. The name hog most commonly refers to the domestic pig in everyday parlance, but technically encompasses several distinct species, including the wild boar...

 or ovine

Domestic sheep

Domestic sheep are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species, in everyday usage it almost always refers to Ovis aries...

 intestine, though beef

Beef

Beef is the culinary name for meat from bovines, especially domestic cattle . Beef is one of the principal meats used in the cuisine of Australia, Europe and America, and is also important in Africa, East Asia, and Southeast Asia...

 intestine may also be used.

Artificial casings are made of collagen

Collagen

Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. It is naturally found exclusively in metazoa, including sponges. In muscle tissue it serves as a major component of endomysium...

, cellulose

Cellulose

Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

 or even plastic

Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products...

 and may not be edible.

For collagen casings, shavings from the inside of beef hides are chopped and processed into a mass similar to bread dough. They can be extruded through a die to the desired diameter, then dried and shirred into short sticks about 18 in long that contain 20 to 30 ft of casing. In a newer process, the dough is coextruded with the meat blend, and the casing is formed by treating the outside with an acid (either liquid smoke or vinegar) to set the casing. Though they may be tougher than natural casings, collagen casings are edible. Collagen casings are smoke and moisture permeable, and are less expensive, give better weight and size control, and are easier to run when compared to natural casings.

Similarly, cellulose, usually from cotton linters, is processed into a paste and extruded into clear, tough casings for making wieners and franks

Hot dog

A hot dog is a moist sausage of soft, even texture and flavor, often made from advanced meat recovery or meat slurry. Most types are fully cooked, cured or smoked. It is often placed hot in a special purpose soft, sliced hot dog bun...

. They also are shirred for easier use, and can be treated with dye to make "red hots". The casing is peeled off after cooking, resulting in "skinless" franks. Cellulose fibers are combined with wood pulp to make large diameter "fibrous" casings for bologna, cotto salami, smoked ham and other products sliced for sandwiches. This type is also permeable to smoke and water vapor. They can be flat or shirred, depending on application, and can be pretreated with smoke, caramel color, or other surface treatments.

Plastic casings are extruded as most other plastic products. They also can be flat or shirred. Generally, smoke and water do not pass through the casing, so plastic is used for unsmoked products where high yields are expected. The inner surface can be laminated or coextruded with a polymer with an affinity for meat protein, causing the meat to stick to the film, resulting in some loss when the casing is peeled, but higher overall yield due to better moisture control.