Concept of casing: casing refers to animal products made by scraping off the large intestine and small intestine of livestock. The main uses are as follows: ① filling the skin of sausage, which is mainly used to ensure that sausage does not deteriorate under certain conditions and time to meet the needs of storage and circulation; ② Catgut thread can also be made into catgut thread, which is used for tennis racket thread, bowstring and surgical suture.

Classification of casing: according to the classification of livestock, it can be divided into pig casing, sheep casing and cattle casing; According to the position, it can be divided into large casing and small casing; There are also salt casings and dried casings.

In addition, high-quality casings should be tough and translucent. What is emerging now is the collagen edible casing.