|Infobox on Casings
|Example of Casings
|Stowage factor (in m3/t)
|Humidity / moisture
Animal intestines used as containers for sausages. Usually packed in casks or kegs.
Casing or sausage casing is the material that 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 pig, cow or sheep intestines.
Collagen casings are produced from the protein in beef or pig skin. 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.
For collagen casings, protein from the inside of beef or pig hides is 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 up to 41 cm long that contain as much as 50 m of casing. In a newer process, a form of dough is co-extruded with the meat blend, and a coating is formed by treating the outside with an acid (either liquid smoke or vinegar) to set the coating.
The latest generation of collagen casings are usually more tender than natural casings. The biggest volume of collagen casings are edible but a special form of thicker collagen casings is used for Salamis and large calibre sausages where the casing is usually peeled off the sausage by the consumer. Collagen casings are smoke and moisture permeable, and are less expensive to use, 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. 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.
Shipment / Storage / Risk Factors
Casings are usually packed in casks or kegs. The produce is liable to ferment if heated. Deterioration and holing (‘salt rust’) of the casings may be a result of poor quality preserving salt. Insufficient brine in the casks may bring about putrefaction.