Casing: In the process of sausage processing, the casing mainly plays the role of processing mold, container, and product performance display.

The casing is in direct contact with the meat, and it must meet the following requirements.

• It must be safe and non-toxic, the chemical components in the casing do not migrate to the meat and do not react with the components in the meat.

• It must have sufficient strength to safely wrap the meat, withstand filling pressure, and withstand the stress of sealing and kinking.

• It also needs to have certain shrinkage and extension characteristics, which can allow the shrinkage and expansion of meat during processing and storage.

• It also needs to have strong cold and thermal stability. After being subjected to certain cold and heat effects, it will not deform, not wrinkle, not become brittle, and will not break.

In addition, according to the product characteristics, some casings need to have certain air permeability, and some need to have better airtightness.

There are two main types, namely natural casings and artificial casings.

In the past, the production of sausage products used elastic animal casings. With the development, it can no longer meet the needs of production. Therefore, many countries in the world have successively developed artificial casings.

1. Natural Casings

Natural casings are animal casings. The gastrointestinal tract and bladder between the esophagus and the erect intestine of animals can be used as casings. It has good toughness and firmness and can withstand the forces generated under normal processing conditions. It has excellent shrinkage and expansion properties and can produce basically the same shrinkage and expansion as the wrapped meat. Commonly used natural casings include the small intestine, large intestine, and cecum of cattle, sheep and pigs, rectum of pigs, the esophagus of cattle, bladder of cattle and pigs, and stomach of pigs. It is made by salting or drying after scraping the mucous membrane. Natural casings are edible and permeable to water and oxygen. It is smoked, has good flexibility, and is a filling material for traditional sausage products. However, its diameter and thickness are not exactly the same, and some even bend unevenly, which has an adverse effect on the specifications and shape of the poured product.

In addition, if it is not kept well, it will also be eaten by insects, causing perforation and odor. It is no longer possible to perform automatic twisting and quantitative filling on the automatic filler machine, and it will cost a lot of manual line segmentation.

Natural casings are generally preserved in two ways: dry or salted.

Dried casings need to be soaked in warm water before use to soften them for processing. It is recommended to fully soak and clean the sausage casings with water to remove the residual dirt on the inner and outer surfaces of the casings and reduce the salt content. Now the commonly used requirements of pig, sheep, and cow small casing, pig, cow large casing, and pig bladder are listed for selection.

1.1. Pig small casing quality requirements: clean, fresh, no peculiar smell, white, milky white, yellow-white, gray-white, etc. Branch standard: divided into seven roads according to the diameter. One road is 24~26mm, the second road is 26~28mm, the third road is 28~30mm, the fourth road is 30~32mm, the fifth road is 32~34mm, the sixth road is 34~36mm in diameter, and the seventh road is more than 36mm in diameter. Binding requirements: 2 pieces are a small bundle, 1 piece is with a length of 5~12m, no more than 3 knots, and each knot shall not be shorter than 1m. Each large bundle is 91.5m long, with no more than 18 knots, and each knot shall not be shorter than 137m. Packing requirements, 60 bundles per barrel, 1300 pieces.

1.2. Quality requirements of pig large casing: clean, fresh, free of impurities, normal odor, smooth terry, all-white or milky white. Branch standard: divided into three roads by diameter. One road is more than 60mm, the second road is 50~60mm, and the third road is 45~50mm. Binding requirements: 1 piece length is 1.15~ 1.5m, and 5 pieces are 1 bundle, 100 bundles per barrel, 500 pieces.

1.3. The quality requirements of sheep small casing: the intestinal wall is tough, no acne, fresh, no peculiar smell, white or blue-white, yellow-white, gray-white, blue-brown. Branch standard: divided into six roads according to their diameter. One road is more than 22mm, the second road is 20~22mm, the third road is 18~20mm, the fourth road is 16~18mm, the fifth road is 14~16mm, and the sixth road is 12~14mm. Binding requirements: 1 piece length is 31m, and 3 pieces are 1 bundle, total length 93m. No more than 16 knots, and each knot shall not be shorter than 1m. 500 bundle per barrel, 1500 pieces.

1.4. Quality requirements of cow small casing: fresh, no acne boils, no holes, normal smell, powder white or milky white, gray-white. Branch standard: divided into four roads according to their diameter. One road is more than 45mm, the second road is 40-45mm, the third road is 35~40mm, the fourth road is 30-35mm. Binding requirements: 1 piece length is 25m, no more than 7 knots, and each knot must not be shorter than 1m. 200 pieces(bundle) per barrel, with a total length of 5000m.

1.5. Quality requirements of the cow large casing: clean, no holes, normal smell. Powder white or milky white, off-white, yellow-white. Branch standard: Divide into four roads according to their diameter. One road is more than 55mm, the second road is 50~55mm, the third road is 45~50mm, and the fourth road is 40~45mm. Binding requirements: 1 piece length is 25m, no more than 13 knots, and each knot must not be shorter than 5m. There are 150 pieces (bundle) per barrel, with a total length of 3750m.

1.6. Quality requirements of dried pig bladder: clean, no holes, with urine tube, no smell, yellow-white or yellow, silver-white. Branch standard: divided into four roads according to the length after folding. One road is more than 35cm, the second road is 30~35cm, the third road is 25~30cm, the fourth road is 20~25cm. Binding requirements: 10 pieces are 1 bundle, 200 bundles per carton, 2000 bundles in total. The best storage temperature of the salted casing is 0~10℃. The casing barrel should be placed horizontally on the wooden frame and turned once a week to make the brine in the barrel move to ensure the quality of the casing. Regular random inspection, if there is leakage of salt brine, salt alteration, etc., it should be dealt with in time.

The storage of dried casings should be paying attention to preventing insects, rat bites, and mildew. The storage room must be kept dry and ventilated, the temperature should preferably be kept below 20℃, and the relative humidity should be 50%~60%. It should be used in a special library, avoid high temperature and high humidity, and do not put together with items with a special smell to prevent odor.

Before processing sausage products, the right casing should be selected according to the product specifications. In each batch of products, the casing specifications and thickness are required to be the same. After the casing is selected, it is soaked and cleaned. The purpose is to wash away the dirt on the surface so that the salted casing can be desalted. Dried casings are soaked in water for ease of selection. Salted casings should be washed inside out, while dry casings are not needed. For large-diameter straight-shaped sausages, the casing should be cut according to the length specified by the finished product, taking into account the degree of shrinkage of the length after baking, cooking, and smoking, and tying the end with a string.

The shrinkage rate of cow’s large casing is 10%~15% during roasting, boiling, and smoking. Natural casings are usually stored in wooden barrels, and the temperature is generally 3℃~10℃. It should be avoided as much as possible in a humid place, and it is best not to be placed in ammonia-refrigerated cold storage. Before use, the salt-cleared casing should be rinsed repeatedly in clean water to fully remove the salt and dirt on the surface of the casing. Dry casings should be soaked in warm water to soften before use.

2. Artificial Casings Mainly Include Collagen Casings, Cellulose Casings and Plastic Casings.

In recent years, artificial casings have developed rapidly. The main reason is that its hygienic, size, and specifications meet the standard, and it can ensure quantitative filling, convenient printing, low price, and less loss in use. The material and characteristics of the packaging material directly affect the shelf life of the filled meat, which can effectively reduce the production cost in mass production. In recent years, there are many types of plastic materials produced in China. Many packaging materials and equipment are imported from abroad, which play an important role in the progress of the meat processing industry. The disadvantage is that they cannot be eaten.

2.1. Collagen Casing

Collagen casings are made of livestock skins, intestines, tendons, etc. as raw materials, soaked in lime water, washed with water, swelled with dilute hydrochloric acid, mechanically destroyed collagen fibers, and turned into a paste after homogenization. Then, high-pressure nozzles produce casings of various sizes, which are dried. Collagen casings have good air permeability, can be smoked and cooked, have uniform specifications, and various varieties, are hygienic, are stronger than natural casings, are suitable for mechanized production and clipping, and can be mass-produced.

It’s divided into two types: edible and inedible. The edible ones are suitable for making Vienna sausages, breakfast sausages, hot dog sausages, and other kinds of cooking sausages. The inedible collagen casing is thicker and has a larger diameter. It is mainly used for the production of air-dried sausages. The shrinkable collagen casing does not need to be soaked before use. Ordinary collagen casing needs to be soaked before filling, that is, soaked in 20~25℃, 10%~15% saline for 5~15min. As the brine concentration increases, casing flexibility and clipping ability are improved. During filling sausages, the relative humidity should be maintained at 40% to 50% to prevent the casing from drying out. When hot working, also pay attention to the problem of dry cracking.

2.2. Cellulose Casing

2.2.1. Cellulose casing is a seamless tubular film made of short linters and pulp as raw materials. This casing has toughness, shrinkage, and coloration. The casing has uniform specifications, is hygienic, has air permeability and moisture permeability can be smoked and can be printed on the surface. Good mechanical strength, suitable for high-speed filling and automatic continuous production. This casing is inedible and does not need to be treated before use, and can be filled directly. It is mainly used to make small-diameter sausages such as hot dog sausage and frankfurter sausage. After cooking, spray with cold water to cool, remove the casing, and then pack.

2.2.2. Fiber casing is made of cellulose viscose plus a layer of paper, which has high mechanical strength and can be clipped. It is permeable to smoke, non-permeable to fat, and inedible, but can be smoked, printed, and can shrink itself during drying. This casing should be soaked before use (the printed soaking time should be longer), and the filling should be firm (the filling can be pierced to vent the air). The surface of the casing should be completely dry before smoking, otherwise, the color will be uneven, and it can be sprayed or cooled in a water bath after cooking. This casing is suitable for processing all kinds of cold-cut sausages, all kinds of dry or semi-dry sausages, smoked sausages, cooked sausages, and rib hams.

2.2.3. Fiber-coated casings are made by pressing cellulose viscose, a layer of paper, and coating the inside of the casing with a layer of polyvinylidene chloride. This kind of casing has good barrier property, which can prevent the water loss of the product during the storage process and strengthen the protection against microorganisms. High shrinkage, full and beautiful appearance, can be printed, but not smoked, not edible. It should be soaked in warm water before use, and the filling should be firm (do not pierce). It can be cooked to the desired core temperature and then cooled with cold water spray or water bath, suitable for all kinds of steamed sausages. Products using this casing do not require secondary packaging.

2.2.4. Cellophane Casing: Cellophane is a regenerated colloidal cellulose film, which has the characteristics of hygroscopicity, gas barrier properties, oil resistance, easy printing, adhesion with other materials layers, and high strength. Roll the cellophane into a tube shape, stick it with the paste, and tie one end with a small string to form the cellophane casing. The cost of this casing is lower than that of a natural casing, and its performance is better than that of the natural casing. As long as it is handled properly, there is almost no rupture.

2.3. Plastic Casing

2.3.1.Polyvinylidene chloride casings are simple or sheet-like casings made of vinyl chloride and vinylidene chloride copolymers. It is characterized by odorless, very low water permeability, air permeability, and ultraviolet light transmission performance. It has certain heat shrinkage and can withstand the high temperature of 121℃. It can be printed, has good mechanical filling performance, safe, and hygienic. Therefore, such casings have been widely used. Polyvinylidene chloride casing is suitable for ham and sausage (such as fish sausage, etc.) produced by high-frequency heat sealing and filling. Manufacturers of this casing are represented by Kureha Chemical and Asahi Kasei of Japan and Dow of the United States. This type of casing is also widely used for the preservation of high-temperature sterilized products at room temperature.

2.3.2. Polyamide casing, also known as nylon casing, is a single-layer or multi-layer casing made of nylon. Single-layer products are breathable and water-permeable and are generally used for smokeable, peeled, and sliced meat products. Multi-layer casings are impermeable and airtight, can be printed, and are not corroded by acids, oils, greases, etc., which are not conducive to the growth of fungi and bacteria. It can also shrink during the cooking process, has strong mechanical strength and elasticity, and is resistant to high-temperature sterilization. It should be soaked in 30 ℃ water before use, and it should be filled firmly (do not pierce) when filling. After cooking, it can be sprayed or cooled in a water bath. It is suitable for making all kinds of cooked sausages, black sausages, liver sausages, head meat sausages, quickly sliced sausages, fish sausages, etc.

2.3.3. Polyester casings are airtight and watertight, can be printed, have high mechanical strength, are not eroded by acids, alkalis, oils, and organic solvents, and are easy to peel off. Polyester casings are divided into two types: shrinkage and non-shrinkage. Shrinkable casings that adhere well to the contents after heat processing. It can be used for the packaging of non-smoked, cooked sausages, poultry rolls, cooked ham, sliced meat, fish, etc., and deep-frozen food. Non-shrinkable casings are mainly used for packaging raw meat and raw sausages and other meats that do not require heating.