Casings 101

The NATIONAL PROVISIONER wishes to acknowledge Joseph R. (Roy) Escoubas, Ph.D., director and professor, Food and Agricultural Products Research and Technology Center, Oklahoma State University, Stillwater, OK, for his work in helping to produce the following Casings 101 Report.
All casings are not alike or created equal — and some feature unique advantages, as well as potential challenges.
Centuries ago, casings were first used to contain and form chopped meat products. Today they’re used not only to contain and form, but also to flavor, season, and protect products. Consumers around the world are so accustomed to sausages being packed into certain forms of casings that a variety of casings can now be used to create and market products.
Casings have since evolved and have opened up the business for sausage manufacturers to do just about anything they want to do. For example, if a processor makes a meat sausage made up of a pork/water/beef sausage, or frankfurter mix, he can make small cocktail links, fill frankfurters, make foot-long hotdogs, or use it to market a basic mix into many different venues for various markets.
In the pages that follow, The NATIONAL PROVISIONER provides casing definitions, application options, as well as information on regulatory compliance, casing waste disposal, handling of casings, and a list of casing manufacturers in alphabetical order.
Casing classifications
Casings are available in a number of classifications:
Natural — Generally speaking, the natural-casing markets include hog stomachs; bungs (hog, beef and lamb caecum); beef bladders; hog, sheep, and lamb casings (small intestine); beef rounds (small intestine of cattle); beef middles (large intestine of cattle); and hog middles (large intestine in hogs).
Typically, hog casings are used for fresh and smoked sausages, as well as breakfast links. Hog bungs are used for liver sausages and certain varieties of dry sausages. Hog middles are used for liver sausage and certain types of Italian salamis.
On the other hand, beef bladders are used for specialty sausages and mortadellas. Beef rounds are used for bolognas, liver sausage, and certain types of fermented sausages. Beef middles are used for liver sausages and dry sausages. Beef bungs are used for specialty pork products, bolognas, and salamis.
Sheep casings are used in the processing of fresh and smoked sausages.
On the average, the small casings used in breakfast sausages are edible, but the larger casings such as bungs, bladders, and stomachs, are generally not considered as edible.
The benefits of natural casings are the remarkably beautiful smoked and cooked appearance. They take on a beautiful color when they’re smoked. Natural casings add to the nutritional value of the product because they are a protein-based material. They tend to be flavor-neutral, but they certainly do not create off-flavors in the sausage product. Natural casings allow products to be placed in up-scale markets primarily due to the eye appeal of the sausage.
On the other hand, natural casings are not inexpensive. Unit price of casing per tonnage output of sausage would be at a manufacturing cost disadvantage when compared to similar products manufactured in regenerated collagen and cellulose casing. Handling of natural casings in preparation for sausage manufacture is more labor intensive and is a bit more delicate than the handling of collagen or cellulose casings. Natural casings must be rinsed because they have been packed and stored with salt—the salt must be washed out of them. It takes a little more finesse and artisan skill to handle natural casings for filling sausage product.
Regenerated collagen — Regenerated collagen casings can be used for any comminuted, coarse, or fine-chopped sausage products. There are very few sectioned-and-formed meats placed in collagen casings.
Regenerated collagen casings are manufactured from a solubilized collagen dough gleaned from animal sources of hides or certain other by-products gleaned from the harvest floor. These materials have been solubilized and re-extruded through an annular die to form a thin-walled tube that is pleated and compressed to form a shirred stick of collagen casing. Shirred sticks of casings are collected, boxed, and sold to processors for automatic filling on high-speed sausage processing equipment. Sausage products that are manufactured in regenerated collagen casings have the snap, bite, and attractiveness that natural casings bring to the product. However, there is often a production cost advantage of choosing natural versus collagen casings in ease of handling and cost of product.
There is another development in regenerated collagen casing products brought to the market by one casing manufacturer. This method used the approach of a co-extrusion of collagen dough with a sausage batter. It has had some success, and today this company has improved the process and commercialized it for fresh sausages and certain types of smoked and cooked sausages.
Regenerated cellulose — There are essentially five kinds of cellulose casings:
1. The first one is small-diameter cellulose casings used to manufacture most skinless frankfurters in the United States. They probably have captured more than 90 percent of the small-diameter frankfurter market in this country.
2. The second group is called large cellulose casings and would be larger- diameter and thicker-walled cellulose casings that would contain the deli-style bolognas. These products are typically about 2 inches in diameter, shaped nicely, glossy, and have an attractive appearance.
3. The third type of regenerated cellulose casing is the very large casing used to shape and hold boneless and semi-boneless hams. These very large cellulose casings are thick-walled and will be sufficiently robust for the ham-filling process.
4. The fourth type of regenerated cellulose casing is the reinforced cellulose casing, commonly called fibrous casings. Fibrous casing is manufactured by bonding regenerated soluble cellulose (viscose) to a highly refined paper similar to tea bag paper. Together they become very robust; they are resistant to stretching and breakage during the sausage filling process. Uniform diameters are the result in a product manufactured in fibrous casing.
5. The last type of regenerated cellulose casing is called moisture-proof (MP) casing. This casing is a fibrous casing with a barrier latex coating. It’s used for sausage products that must be cooked or need an extensive shelf life. It’s an expensive but effective product for water cooking and extending product shelf life. MP casings, however, are expensive. Nylon casings are also a barrier and less expensive. The difference is MP casings are coated-fibrous casings, and they offer exact-diameter control. The nylon casing, although less expensive and a barrier, doesn’t offer the same exact-diameter control.
The small-diameter cellulose casing is used to manufacture a variety of smoked sausages and some types of fresh sausages, such as chorizo or Italian sausage. The large cellulose casing would be used for bolognas and salamis. The very large cellulose casings are typically for boneless and semi-boneless hams. The fibrous casing would be used for all the fermented sausages, large-diameter cooked sausages, and deli-style meats.
The small-diameter cellulose casing is manufactured and formed in shirred sticks just as the small-diameter collagen casing. The difference is the small-diameter cellulose is much stronger and elastic than collagen and is easier to manufacture product.
Productivity is a strength for cellulose casings, and the cost is lower than collagen casing. Cellulose is a moisture- sensitive membrane, and it will allow water-soluble material like smoke to move across it to the surface of the sausage. Products manufactured in small-diameter cellulose casings are usually smoked, cooked. and the casings are removed before product goes to market. The large-cellulose casing are used for deli bolognas, as well as boneless and bone-in hams.
Fibrous casings are strong, smoke permeable, and can be peeled easily after products have been cooked and cooled. All fibrous and cellulose casings must be removed before product is consumed. Spent casing is the one key downside of cellulose casings.
Plastic/nylon —Nylon casing is a relatively inexpensive and attractive barrier casing. It allows a way to produce a high volume of items that need shelf life or products that must be water-cooked and then enter the market — and product doesn’t have to be repackaged.
There are both cost and high productivity benefits. They are also delivered in shirred casing units with a first clip attached to begin the stuffing process. They are barrier casings, and they offer tremendous graphics for attractiveness to the package. They can be offered in various sizes. They typically range in sizes from one to five inches in diameter. The nylon casing’s challenge has been the inability to be smoked because nylon/plastic casing is a barrier. One company doing business in the United States has brought smoke-impregnated nylon casings to market. This product could have great inroads into the traditional fibrous casing market.
Casing technology
atural casings are gleaned in the animal harvest facility. These casings are thoroughly cleaned, washed, salted, and packed to be shipped to the natural casing manufacturer. Natural casings are finished at the manufacturer’s location by salt removal, additional washing, and trimming and forming into the respective units expected for each type of natural casing. The trimmed and finished natural casing is resalted and packed for shipment and storage.
When the sausage manufacturers receive the packed natural casing, they must be desalted and rinsed with water before use. These casings are typically manually placed onto filling tubes where the sausage filling and forming occurs. These filled casings are placed onto stainless steel smoke sticks and then into a thermal processing oven where they are smoked and cooked. Subsequently, these cooked natural casing products are chilled, sometimes peeled, and then packaged and boxed for shipment to consumers
Regenerated cellulose casings were brought to the commercial trade by the efforts of E. O. Freund in the early 1900’s in Chicago. He developed the commercial process of regenerated cellulose extrusion into various lengths and sold them in the packing plants in the Chicago stockyards. His success continued and he founded the Visking Co., later to become the Films-Packaging Division of Union Carbide Corp., and today is known as the Viskase Corp.  
Regenerated cellulose casings are manufactured from any process that will dissolve cellulose sourced from either cotton or wood pulp. To date, the preferred method has been the viscose process. Being a viscous alkali cellulose, viscose is extruded through an annular die into an acid bath. A seamless tube is formed and is strengthened and cleaned by repetitive water baths. Finally, the tube stock is glycerinated to keep it supple and resistant to damage, and it is typically collected in rolls for staging in the finishing process.
To finish the cellulose casings, the rolls of tube stock are pleated and compressed into shirred tubes of specified length. These shirred sticks of cellulose casings are collected into units of specified stick count and shipped to the sausage manufacturer where they are most often placed on automated filling equipment where frankfurters or sausages are formed and linked. The filled and linked sausage is placed in some fashion into a thermal-processing oven where the smoking, cooking, and chilling occurs. Finally, the casing is removed from the cooked product, and the peeled product is packaged, boxed, and shipped to the consumer.
Regenerated collagen casings were first developed in Germany as an alternative to the irregular natural casings. Work of Oscar Becker in the early 1900’s successfully developed a process to manufacture a collagen casing tube. Significant process changes and improvements were added by other German entrepreneurial businesses. The Devro Casing Co. was founded based on somewhat different process technology in the manufacture of regenerated collagen casings. Regardless of the process type, regenerated collagen casings have been strongly entrenched in the sausage casing market.
Regenerated collagen casings are most typically sourced from dehaired and chemically prepared cattle hides. The hide preparation is chopped and mixed with an acid to produce a viscous gel and is extruded into an alkaline environment to produce a collagen tube. This tube is washed through repetitive water baths, plasticized to maintain a supple nature, cross-linked, dried, and shirred into sticks of collagen casings. These shirred and finished casings are packaged into units, boxed, and shipped to the sausage manufacturer.
Regenerated collagen casings are typically placed onto automated filling and linking equipment where the casing is filled with a sausage batter, linked as appropriate, and subsequently smoked, cooked, chilled, and packaged for shipment to the consumer.
ylon casings are usually very complex multi-layered, co-extruded structures. The type of polymers in the respective layers and the wall thickness of the casing usually results in a barrier casing. The casing is extruded, oriented to create stretch and shrink properties, and collected into rolls to be finished as appropriate. Finishing occurs usually by shirring into predetermined unit lengths, casings are then boxed and shipped to the sausage manufacturer. The sausage manufacturer simply fills and forms the casing, and the product is placed into an oven or water bath to cook. The cooked and chilled products are packaged as chubs, sometimes peeled and sliced, packaged, and shipped to a consumer.  
Unique casings
There are many unique casings used in the trade including smoke-containing casings, spice/flavoring-containing casings, unique-shaped or shaping casings, antibacterial casings, high-barrier casings, natural casings that are pre-formed, and more. Casing suppliers offering natural casings often offer sewn casings where they will take a particular kind of a casing and cut it based on a pattern, and then re-sew those casing pieces together so it conforms to a particular shape. Product is then filled, cooked, and delivered to the market. Sewn natural casings are truly unique.
Another unique casing is becoming commonplace, almost a commodity in the United States — smoked impregnated fibrous casings. They moved into the market in the early ‘80s and now they’re state-of-the-art. Almost any ham that’s brought to market like a buffet ham or boneless ham use them. Almost all of those manufactured throughout the United States are in smoked fibrous casings. There is a manufacturer who has started selling small-diameter smoked cellulose casings in the United States. This company has bought that business into the commercial trade, and this has never been done before.
This company is also trying to market antibacterial casings. During the finishing process in small-diameter cellulose casings, they put an antibacterial mix on the inside with a shirring solution to allow the shirring and pleating.
In addition to the previously mentioned moisture-proof (MP) casings, another unique casing being offered is spice mix-impregnated fibrous casings that are treated on the inside. When product is filled and cooked in such a casing, the spice mix adheres to the meat product’s surface. When the casing is pulled off, it has the spice-mix rub on the product’s surface. Europeans are particularly strong on that application. This typically hasn’t been a popular product in the United States because Americans tend to want to produce products that allow high productivity at low costs. That kind of a casing doesn’t fit that demand. It takes an artisan approach, and they’re expensive.
Regulatory compliance
All casing suppliers are under the jurisdiction of the Food and Drug Administration (FDA) because they’re manufacturing a food container that’s in direct contact with food. All components used in their casing materials must comply with Title 21 Code of Federal Regulation—whether it’s a natural casing and the way a natural casing is manufactured, the collagen casings and the procedures approved for regenerated collagen, the regenerated cellulose casing and procedures approved for regenerated cellulose, and all materials used to plasticize those casings to keep them flexible, supple, and damp.
The second step is complying with United States Department of Agriculture (USDA) regulations because casings are used in USDA establishments. You must supply to the establishment owner a Continuing Product Guarantee that meets the requirements of Title 7. It’s different than an individual guarantee in that an individual guarantee is for a particular item with a particular specification. A Continuing Product Guarantee meets the requirement of a non-changing item.
The USDA occasionally does a compositional review check. USDA offices will put a call out to casing suppliers for them to update their files to make sure that everything is in compliance. That happens every so often.
Once casings come into a USDA establishment, the establishment must comply with USDA regulations. Cellulose casings can’t be eaten by the consumer and must be removed before consumption. The wording on the cellulose casing box must identify that the casings remaining on the product must be removed. Any collagen casings that cannot be eaten must be identified as inedible and removed. Those natural casings that should not be consumed must also be identified to be removed.
Any product that goes to the retail market cannot mislead or cause the end-user to assume that it is something different. In other words, if a processor chooses to send a smoked sausage to retail in a fibrous casing and the color of the casing is brown, the end-user might not necessarily associate that brown color with the casing— and may think that the brown color is the color of the product. That is considered misleading, which the USDA doesn’t accept.
Casing waste disposal
Products with casings that go into the retail trade have the casings disposed of by the end-user, which include nylon or fibrous casings. Most all other casings that cannot be consumed are removed inside of the meat plant. These waste casings then become a waste-handling issue. Some states have put taxes on casing waste. Casing waste and disposal is becoming a tremendously large issue in many states. It’s looming, but there are new technologies being investigated to discover ways to get rid of casings while in the meat plant to avoid landfilling this waste.
There is a process technology for batch dissolving of cellulose casings using cellulase enzymes in a batch. Recycling casing waste into new casings has been investigated unsuccessfully for years.
Handling casings
Adhere to the normal practice of filling product, and follow proper handling of good manufacturing practices (GMPs). As casings are removed from meat products, there is the potential for contamination or recontamination. Significant attention has been focused on minimizing recontamination at the point of casing removal of hot dogs and frankfurters in meat processing plants. It has been a real issue, but processors have made a great effort to deal with it.
There is also a risk in food preparation of sausages. For example, almost all hot dogs are fully cooked when they enter commercial trade. Many times the end-user will not reheat the hotdogs or will do a quick microwave. Any low-level contamination that could have occurred during packaging could create risk for the consumer eating this product.
Create a checklist
Before choosing a certain type of casing, create a checklist of questions requiring answers. First, learn what the competition is using. And some casing types require specific equipment. For example, if someone manufactures product with equipment that would be used for small-diameter cellulose casings and they decide to move to another market and to be competitive in that market they have to use natural casings — that could be a real challenge. Such a processor has to have people who understand:
How to buy natural casings
Forms they are available in
How to handle natural casings when they arrive at the plant (how to clean them and have them prepared)
The artisan nature of filling product to be able to handle and smoke product. The labor works differently on the floor. They’re going to have to make a huge processing and attitude change.
The biggest consideration new processors or those wanting to expand into sausage manufacturing must consider is the cost. What do they want to pay for filling equipment? The low-cost way to fill is using a small hand stuffer—you can accomplish that with natural casings and collagen or cellulose casings. Processors can use almost anything they want to use if they’re using a small hand stuffer.
But for middle-size or larger manufacturers wanting to move from one type of a venue or marketable product to something much different, they must determine is it going to take something remarkably different than they’re currently using? When’s the payback? NP