Synthetic casings are used in the manufacture of sausages instead of natural casings made from the intestines of animals (sheep, cows or pigs).
Synthetic casings are made of collagen, cellulose, or even plastic and may not be edible. Artificial casings from animal collagen can be edible, depending on the origin of the raw material.
Here are the several types of synthetic casing:
Collagen casings are mainly produced from the collagen in beef or pig hides, and the bones and tendons. It can also be derived from poultry and fish. They have been made for more than 50 years and their share of the market has been increasing. 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.
The collagen for artificial casings is processed extensively and, as a raw material, it is similar to bread dough prior to final production. It is then extruded through a die to the desired diameter, dried and shirred into short sticks up to 41 cm long that contain as much as 50m of casing. In a newer process, a form of dough is coextruded with the meat blend, and a coating is formed by treating the outside with a calcium solution to set the coating.
The latest generation of collagen casings are usually more tender than natural casings but do not exhibit the “snap” or “bite” of natural casing sausages. The biggest volume of collagen casings are edible, but a special form of thicker collagen casings is used for salamis and large caliber sausages where the casing is usually peeled off the sausage by the consumer. Collagen casings are less expensive to use, give better weight and size control, and are easier to run when compared to natural casings.
Cellulose, usually from cotton linters or wood pulp, is processed to make viscose, which is then 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. Cellulosic viscose solutions 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.
Fibrous casing is a cellulose-based casing strengthened with natural long-fibered abaca paper, sometimes called manila hemp fiber, which combines exceptionally high tensile strength with consistent extrusion properties in a form that renders it ideally suited for sausage casings. Due to its strength and dimensional stability, fibrous casing is traditionally seen as one of the most versatile and comprehensive packaging materials.
Plastic casings are extruded like 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 nonsmoked 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. Plastic casings are not commonly used any more due to health hazards.
Plastic casings are generally made from polymers such as Polyamide, Polypropylene or Polyethylene. Polyamide (Nylon) plastic casings are the most commonly used in production of cooked sausages and hams such as luncheon meat and bologna. Polyamide casings come in two main varieties: Oriented and nonoriented. The oriented polyamide are shrinkable casings and will shrink during the cooking process thereby reducing the water loss. Nonoriented polyamide casings remain the same diameter during the cooking process and thereby allow for expansion of the meat during cooking.