Natural casing is the cleaned, processed intestinal lining of an animal, used as the outer skin of a sausage. Specifically, it’s the submucosa, a thin but strong layer made of naturally occurring collagen that sits just beneath the inner lining of the small intestine. This is what gives traditional sausages their characteristic curved shape and the satisfying “snap” when you bite into them.
What Natural Casings Are Made Of
An animal’s small intestine has four distinct layers. During processing, three of those layers are stripped away, leaving only the submucosa. This single layer is remarkably tough relative to its thinness, because it’s essentially a dense sheet of collagen fibers. It’s fully edible, breathable (which matters during smoking and drying), and flexible enough to expand as it’s stuffed with meat.
The three most common sources are hog, sheep, and beef intestines, and each produces a casing with different properties.
- Sheep casings are the smallest and most tender, typically 20 to 28 mm in diameter. They’re used for breakfast sausages, snack sticks, hot dogs, and wieners.
- Hog casings are the most widely used, ranging from 32 to 42 mm. They’re the standard for bratwurst, Italian sausage, kielbasa, and most fresh sausage links.
- Beef rounds and middles are much larger, starting around 1 inch and going up to 8 inches in diameter. Beef rounds hold salami, pepperoni, and summer sausage. Beef middles have a heavier wall with some fat, making them well suited for dry-cured and semi-dry sausages like liverwurst and bologna.
Why Natural Casings Taste Different
The main reason sausage makers and consumers prefer natural casings is texture. A natural casing has a firm, elastic bite that collagen and cellulose casings can’t fully replicate. When you grill or pan-fry a sausage in a natural casing, the exterior crisps and tightens slightly, and the casing resists just enough before giving way. That’s the “snap” people talk about.
Because the casing is a biological membrane, it’s also permeable to smoke. This matters for smoked sausages like andouille or kielbasa, where the smoke flavor needs to penetrate evenly. Artificial casings can be engineered for permeability too, but natural casings do it inherently.
The tradeoff is consistency. Since each casing comes from an animal, diameters and wall thickness vary from piece to piece. Two links from the same batch might differ slightly in size. For large-scale commercial producers, that variability is a drawback. For home sausage makers or artisan producers, it’s considered part of the character.
Natural vs. Collagen and Cellulose Casings
Collagen casings are sometimes confused with natural casings because they’re also derived from animal tissue. The difference is in how they’re made. Collagen casings are manufactured by extracting collagen from hides and bones, then reconstituting it into a uniform tube through an industrial process. They’re classified as artificial casings despite their animal origin. They don’t require soaking, they come in perfectly consistent sizes, and they’re easier to work with on a production line. But they lack the elasticity and snap of natural casings.
Cellulose casings are made from plant fiber and are not edible. They’re used to shape the sausage during cooking, then peeled off before packaging. Skinless hot dogs are the most familiar example.
How to Store Natural Casings
Natural casings are preserved in salt, either packed in dry salt or submerged in a salt brine. Stored this way in an airtight container at 40°F (4.4°C) or below, they’ll keep for at least a year. The key rules are simple: keep them cold, keep them salty, and never freeze them. Freezing damages the collagen structure and makes the casing fragile.
If you open a package and only use part of it, the leftover casings need to be re-salted thoroughly, drained of excess water, and sealed back in their container in the refrigerator. Skipping the re-salting step, even for casings you plan to use the next day, dilutes the brine and shortens their usable life. For long-term storage, temperatures between 32 and 39°F are ideal.
Preparing Casings for Stuffing
Salted casings are stiff and need to be rehydrated before you can use them. Start by rinsing the casings under cool running water to flush off the salt. Then soak them in warm water, around 98°F (37°C), which is roughly body temperature. Keep them fully submerged and avoid water hotter than 104°F (40°C), which can weaken the casing. Soak for at least 45 minutes. If you’re planning ahead, you can also soak them overnight in cold tap water.
After soaking, it helps to run water through the inside of the casing to open it up and check for any holes or weak spots. Slide the casing onto your stuffing tube while it’s still wet. Natural casings are much easier to handle when they stay moist throughout the process.
Labeling Rules in the U.S.
Under USDA regulations, sausage makers must identify the animal source of a natural casing if it differs from the meat inside. A pork sausage in a hog casing doesn’t need a special callout, but a pork sausage in a sheep casing does. This information can appear on the front of the package or in the ingredient list. Producers are also required to keep records documenting the source of every casing they use.