Selecting the right casing for your product
There are several choices to consider for casings, including natural, manufactured collagen, cellulose, fibrous and moisture proof casing materials.
Each of these has its own unique characteristics and will impact product properties in different ways.
Natural casings are more expensive than many other casing types, but there is increased interest in them because of their association with premium products. Natural casings are derived from the gastrointestinal tract of meat animals (sheep, hogs, beef) with sheep casings smallest (16-28 mm), most tender and best used for fresh sausage and small-diameter smoked and cooked sausage.
Hog casings are somewhat larger (30-42 mm) and less tender, whereas beef casings are the largest (35-125 mm), toughest and best suited for larger-diameter products in which more strength is needed. These large-diameter casings are sometimes tied with string loops or netting to provide added strength needed to permit hanging the stuffed product in the smokehouse.
Natural casings are essentially all collagen because the inner mucosa and outer fat/muscle layer of unprocessed casings are removed, leaving the middle collagen layer to be used as a casing. An important property of collagen that is applicable during processing is that wet collagen is permeable but becomes very soft and weak, whereas dry collagen becomes hard and less permeable to moisture and smoke.
Consequently, natural casings must be handled correctly during processing to achieve the desired tenderness and permeability needed for a specific product. Initial smokehouse steps should include a mild drying environment to retain strength yet still allow smoke penetration. After smoking, further drying can be used to render the casing almost completed and irreversibly impermeable to moisture. The casing can then tolerate a variety of final cooking treatments, even as extreme as steam cooking, without excessive moisture loss from the product.
Manufactured collagen is animal collagen (usually from beef hides) that is first solubilized. It is then reformed into a uniform collagen tube of various sizes. These casings have the same properties as natural casings in terms of a need for proper processing treatments for tenderness and permeability but have an advantage in terms of greater uniformity and consistency than the natural casings.
Manufactured collagen casings also avoids the issues of potential microbial loads and occasional rancid surface fat residues that sometimes occur with natural casings. Manufactured collagen casings also have an advantage in that they can be designed for specific product applications. For example, fresh sausage casings can be kept tender since there is no high-humidity cooking process involved.
Casings for cooked or dry and semi-dry products are manufactured to accommodate the cooking/smoking/drying processes involved with these products. Because of the specificity of applications for manufactured collagen casings, it is a good idea to work closely with casing suppliers to assure that the casing performance is appropriate for the product under consideration.
One form of cellulose casings that is widely used is the small-diameter, peelable casings such as those used for skinless frankfurters. These casings are precisely sized and highly uniform to facilitate use of high-speed stuffing and linking equipment.
During subsequent smoking and cooking of the product, a meat protein “skin” is formed that permits removal of the casing and production of “skinless” sausage. Obviously, the protein surface skin formation is a critical step and some form of acid, either in natural smoke or liquid smoke, is important to this. It is also important that these casings are stuffed to their recommended diameter because overstuffing can result in poor peel ability.
Casing moisture is also important to facilitating peel ability and a final cooking step with steam or high humidity may be helpful for improving peel ability.
Another form of cellulose casing for large-diameter products is the fibrous casing. These consist of cellulose with paper fibers that increase the strength of the casing. As with cellulose, fibrous casings are very uniform and compatible with high-speed machine stuffing. These casings are typically soaked in water prior to use to improve flexibility and provide a small degree of expansion during stuffing.
There are also some specialized applications provided for use of fibrous casings. For example, sausage makers may use fibrous casings with an internal coating that adheres to the product as it dries for both dry and semi-dry products. However, if the product, such as pepperoni, is to be sliced, than a peel able fibrous casing is preferable.
Fibrous casings are also available as pre-stuck or drilled casings in which tiny holes in the surface or larger holes in the end are added to allow air to escape during stuffing. These fibrous casings are designed for use with chunked or whole muscle products such as sectioned and formed hams or boneless hams.
Moisture proof casings
Several different kinds of materials including polyethylene, nylon and several others are used to manufacture moisture-proof casing that is frequently used for water-cooked or steam-cooked products.
These casings are typically impermeable to both moisture and smoke, so smoke flavoring such as liquid smoke must be incorporated into the meat mixture. Color is incorporated into many of these casings such as those frequently used for Braunschweiger.
Advantages to these casings include minimal cooking shrink for the product and a finished product that is very well protected from external contamination as long as the casing is intact.