Casing is a livestock product made by scraping the large intestine and small intestine of livestock. Mainly used as a jacket for filling sausages and enemas; Catgut can also be made into catgut, which is used to make tennis racket strings, bowstrings and surgical sutures. Casings are divided into pig casings, sheep casings and cattle casings according to animal types. According to the position, there are big casings and small casings. Intestines are divided into mucosa, submucosa, muscularis and serosa from inside to outside. According to the different requirements of livestock and their processed products, the treatment of the above four layers is different. A good casing should be tough and translucent. What is emerging now is the collagen edible casing.

(1) salt casing

The processing flow of salted casing is roughly as follows: clean the fresh sausage, soak it for 18 ~ 24 hours, and then peel and scrape it. Then cleaning, watering, inspecting, cutting into pieces of sausage with holes, making a handful every 5 or 10 (the total length is about 90 meters), and pickling with about 0.5 kg of refined salt for one day and night to obtain semi-finished sausage. Smooth sausages are rinsed, inspected, salted and drained to become finished products.

(2) Dry casing

The processing technology of dry casing is similar to that of salt casing. After peeling and scraping, add 2.5 liters of 5% sodium hydroxide solution to every 70 ~ 80 tablets, stir evenly and remove grease. Rinse again, add salt with 0.8 ~ 1 kg refined salt every 100 m for 12 ~ 24 hours, then wash with water to remove the salt, air dry and flatten, and then pack and sell. Good quality pig casings are thin, tough, transparent and uniform (the thicker casings are better); The salted casing is light red, white or milky white. Dry casings are mostly light yellow; It has a certain aroma.

Whether the casing is used and stored properly is also very important for the casing to play its role. The storage environment of casing generally requires drying, ventilation and dark storage below 25℃. Please use it according to the method recommended by casing factory. Improper use will bring bad influence to the quality of sausage. ① The shell was bruised before or during use. In severe cases, the casing will burst during enema or sterilization. In lighter cases, the barrier performance of sausage casing will be reduced because its structure is destroyed during the storage or sale of sausage. Sausages will be oxidized and deteriorated in advance, or bacteria will enter the sausage and cause the sausage to rot, thus losing its edible value. ② Storage of casing under high temperature and high humidity will cause sausage deformation, decrease shrinkage and change specifications. (3) Long-term storage of casings will cause casing deformation and losses due to incomplete storage conditions. It is generally recommended that the storage period is 3 months.