Pork casing is made from the cleaned and processed intestines of pigs, specifically the submucosa, a collagen-rich middle layer of the small intestine. After the inner lining and outer muscular layers are stripped away, what remains is a thin, flexible tube of natural collagen fibers that becomes the edible casing wrapped around sausages like bratwurst, Italian sausage, and kielbasa.
Which Part of the Intestine Becomes Casing
A pig’s intestinal wall has multiple layers, but only one of them ends up as casing. The submucosal layer sits between the inner mucous lining and the outer muscular wall. During processing, those surrounding layers are mechanically scraped away, leaving behind a translucent tube made almost entirely of collagen, the same structural protein found in skin, tendons, and connective tissue throughout the animal’s body.
This collagen layer has a distinctive woven structure with wavy, diagonally oriented fibers. That architecture isn’t random. In the living animal, it allows the intestine to stretch and contract during digestion. In a sausage casing, those same properties translate into elasticity, strength, and the satisfying “snap” when you bite through a well-made sausage.
How Raw Intestines Become Usable Casings
The transformation from intestine to casing starts at slaughter. The small intestines are pulled free, and their contents are squeezed out end to end. The intestines are then cut into manageable sections, typically around four feet long, and run through a series of cleaning and scraping steps that remove the mucosal lining on the inside and the muscular and fatty tissue on the outside.
In commercial production, this scraping is done by machine. At a smaller scale, it’s done by hand with a dull blade or the back of a knife, working against a flat surface. Either way, the goal is the same: isolate that thin, strong submucosa layer and wash it thoroughly. The cleaned casings are then packed in salt or a salted brine solution, which preserves them and draws out remaining moisture.
Why Natural Pork Casings Affect Flavor
Natural pork casings aren’t just a container. They’re permeable to water vapor, gases, and smoke, which means they actively participate in cooking. During smoking, flavor compounds from the wood pass through the casing and into the meat. During drying, moisture escapes through the casing walls, concentrating flavor and firming the texture.
This permeability is especially important for fermented and dry-cured sausages. As the sausage loses water and shrinks during maturation, the elastic casing contracts along with it, staying tight against the meat filling. If the casing can’t keep up with those volume changes, the sausage develops structural defects like air pockets or separation between the casing and the filling.
As smoking and drying progress, the casing gradually becomes more rigid and less permeable. Lactic acid from bacterial fermentation accelerates this tightening. The result is a casing that starts out flexible enough to stuff and ends up firm enough to hold its shape on a plate.
Sizes and What They’re Used For
Pork casings come in graded diameter ranges, measured in millimeters, and each size corresponds to a different style of sausage:
- 29–32 mm: Small bratwurst, link sausage, landjaeger
- 32–35 mm: Standard bratwurst, Italian sausage, rope sausage
- 35–38 mm: Polish sausage, kielbasa
- 38–42 mm: Bologna and other large-format sausages
The natural variation in intestine diameter from one animal to the next means casings are sorted and sold by size range rather than a single exact measurement. This is one reason artisan sausages often have slight differences in thickness from link to link.
How Pork Casings Compare to Other Natural Casings
Sheep, hog, and beef intestines all produce natural casings, but they differ in important ways. Sheep casings are thinner and more delicate, making them the standard choice for breakfast sausages, hot dogs, and snack sticks where a tender bite is desirable. Pork casings are thicker and sturdier, which gives them that characteristic snap and makes them better suited for heartier sausages. Beef casings are the largest and toughest, used for salami, bologna, and other big-diameter products.
Collagen casings manufactured from processed animal hides offer a synthetic alternative that mimics natural casing properties. They’re more uniform and easier to work with on a production line, but many sausage makers prefer natural pork casings for their texture, permeability, and the way they respond to smoke and heat.
Storage and Shelf Life
Salted natural pork casings are surprisingly shelf-stable. Kept in brine in an airtight container, they last at least a year in the refrigerator. The heavy salt concentration prevents bacterial growth and keeps the collagen from breaking down.
Before use, salted casings need to be soaked in clean, warm water for at least an hour, changing the water a few times, to rehydrate them and wash out excess salt. This restores their flexibility and makes them pliable enough to slide onto a stuffing tube. If you soak more casings than you need, just pack the extras back in salt, seal them in an airtight bag, and return them to the fridge.
How Pork Casings Are Regulated
In the United States, natural casings fall under FDA jurisdiction rather than USDA mandatory inspection. Facilities that produce casings can voluntarily request USDA inspection and certification, which allows them to apply the USDA mark of inspection to their products. This is particularly relevant for casings destined for export, where importing countries often require government certification that the casings came from healthy animals that passed veterinary inspection and were handled under sanitary conditions. Imported casings entering the U.S. must be accompanied by similar certification from the exporting country’s government.