While metal and plastic moulds are used to shape loaves and some other comminuted meat products, natural and artificial casings are used as forms and containers for sausages. The casings bind and protect the delicacy of the sausage mixture; they regulate contraction and expansion of the sausage.
Sausages have historically been manufactured in natural casings. Natural casings are almost exclusively prepared from different parts of the alimentary canal of pigs and ruminants. Pig caings are derived from the stomachs, small intestines (pig casings, smalls or rounds), large intestines (caps and middles) and terminal straight end of the large intestines (bungs). Cattle casings are obtained from the oesophagus (weasands), small intestines (rounds or runners), caecum (bungs), large intestines (middles) and urinary bladders. Only the small intestines of sheep are used for sausage casings.
The walls of the entire intestinal tract consist of four distinct tissue layers: mucosa, submucosa (rich in collagenous fibres), circular and longitudinal muscle layers and serosa or external layer.
The total length of the pig's large and small intestines is about 19 to 24 m.
After separation from the adhering fat, the stomachs are further processed in two ways. If the stomachs are to be incorporated into the sausage, they are scalded and well cleaned. If they are to be used as casings, only a small opening is made through which they are cleaned by flushing and then kept in salt until used. Pig stomachs are used for stuffing head cheeses etc.
Fig. 19 HOG CASINGS
The pig's small intestines have an average length of 15 to 20 m and vary in diameter and strength according to the breed of animal and type of feed consumed. Today fresh cleaning methods of processing casings without fermentation are adopted.
After removal of fat and mesentery (“running”), cleaning and removal of the intestinal contents (“stripping”) by machine or by hand, the intestines are first crushed between rollers of a mucous crusher and then slimed, i.e. passed between a set of rollers or strippers to remove mucosa and other unnecessary layers of the intestinal wall (both muscle layers and serosa), leaving only the submucosa. The slimed intestines are graded (inflated by air or water), salted with 40 percent salt and kept until used.
The intestines of the pig (and particularly those of sheep) have long been processed by fermentation. The process of fermentation enables their sliming by hand without using machines. The method is as follows: after being turned inside out, the casings are soaked in water at 20° to 24°C overnight or until the mucosa and muscle layers become adequately tender to allow their manual removal (“sliming”). Such treatment causes the processed pork rounds to be characteristically composed of only the submucosa layer; the connective tissue-rich submucosa is not loosened and the final product is of good mechanical strength.
Pig rounds are packed in hanks of 100 yards (300 feet or 91.4m), consisting of 15 to 20 pieces, measuring about 18 ft each (5.5 m). Pig casings are graded according to diameter as narrow (28 mm and under), narrow medium (28 to 32mm), regular medium (32 to 35 mm), medium (35 to 38 mm), wide (38 to 42 mm) and extra wide (42 mm and over). Pig casings are used for fresh sausages, chorizos, frankfurters etc.
After separation from the fat, the large intestines are stripped of their contents, flushed out with water, turned over, chilled in brine overnight, stripped free of mucosa and serosa, leaving the submucosa and both muscle layers, and finally salted. The industrial term for the processed caecum is “cap”; the first portion of the large intestines is not utilized as sausage casings and the middle portion of the pig's large intestine is known as “middles”.
The pig's large intestines are also used for preparations as chitterlings or filler meat. In sausage making, they are used for stuffing liver sausages, some salamis etc.
After the bungs (terminal end of large intestines, i.e. the ends of the intestinal tract starting from the anus) are pulled free from their setting, they are stripped under a spray of water which washes away the contents. The bungs are soon afterward slimed, inflated for grading and thoroughly salted.
Pig bungs are 1 to 1.5 m in length. Their diameters vary from about 30 to more than 50 mm. Pig bungs are primarily used for liverwurst, cervelat, dry sausages etc.
Pig bladders are emptied, trimmed free of fat, turned over and bleached in ice water or brine for a period of time. They are preserved by salting or inflated by air and dried.
The total length of the small and large intestines is about twenty times the length of the body in cattle.
After the musculature is removed from the outside the weasands are washed turned inside out, cleaned, inflated with air, graded and dried. They are used for large sausages; their length varies from 45 to 60 cm and over
The small intestines of cattle have an average length of 40 m the average diameter is 5 to 6 cm.
The rounds are turned inside out and slimed; the mucosa and serosa are removed from the intestines leaving the submucosa and both smooth muscle layers which, in beef intestines are much thicker than in pig intestines. After submerging in water and washing, rounds are calibrated, tied and salted. Salted rounds are marketed in sets not less than 100 yards (91.4 m) each set containing a maximum of five pieces. Beef rounds are used for stuffing ring sausages, all beef sausages in Near East countries etc.
Beef rounds are classified in wide (38mm and over), medium (35 to 38 mm) and narrow (35 mm and under).
Fig. 20 BEEF CASINGS
The caecum or blind gut has an average length of 75cm and diameter of 12 cm. Caecums are substantially processed in the same way as beef middles. Beef bungs are used for stuffing cooked sausages, capicola, large bologna etc. Their diameter varies from 76 to 102 mm.
The middles are separated from the ruffle, flushed out with water, trimmed free of fat, turned over, slimed and salted. Beef middles also include the “straight” casing and are packed in sets each measuring about 17 m after salting and composed of 5 pieces. Beef middles (narrow end, wide end and fat end) are used as containers for different salamis and other large-diameter sausage products.
Beef bladders are washed, turned over and either salted or inflated with air and dried. They are used for mortadellas, different sausage specialities etc. Beef bladders are usually graded in large, medium and small sizes.
The small intestines (sheep or goat small casings or rounds) are pulled free of the adhering fatty tissue, stripped free of their contents, immersed in water (10°C) and fermented or directly slimed by machines. After the removal of the mucosa, serosa and both muscular layers, the casings are chilled, inflated for grading, salted and stored.
Sheep casings are packaged in hanks (100 yards or 91.4 m) and may be extra wide (25 mm and up), wide (22 to 24 mm), medium (20 to 22 mm), narrow-medium (18 to 20 mm) and narrow (16 to 18 mm). Sheep casings are primarily used for fresh frying sausages and for frankfurters, wieners, chipolatas, etc. Sheep fore-stomachs are used for haggis and some other meats and fancy meat specialties.
Fig. 21GOAT AND SHEEP CASINGS
Sewn casings are made by sewing beef middles and small pig bungs together. Special sewing machines are marketed for this purpose.
Sewn beef middles are made by sewing two or more pieces of beef middles together. They are used for stuffing different fresh or semidry salamis, bologna etc. They are made in different diameters with stuffing capacity from 0.7 to 2 kg.
Sewn pig bungs are usually manufactured in about 70 cm length with a diameter of 5.5 to 7 cm resulting in a stuffing capacity of 1.8 to 2 kg. Larger sizes of sewn pig bungs are also sometimes made by sewing more than two pig bungs together.
All casings must be inspected before being used. The surface of all casings should be completely free of any remaining adhering fat. All natural casings, except sheep casings, before being used should be turned inside out, washed and trimmed of fat. Salted casings should be soaked in water for desalting; dried casings are watered for softening. Any casing that is left over the same day must be resalted.
Artificial casings offer a uniform cylindrical shape and the choice of any specific diameter and suitable tensile strength as well as resistance to damage. They are filled uniformly and, after filling, sausages can be linked by machine or by hand into required lengths. The artificial casings are made from cellulose, collagen, plastic and other materials.
Cellulose casings are manufactured in different sizes, ranging from 1.5 to 15 cm; their important advantage is size uniformity. Cellulose casings are not soaked in water prior to stuffing. Small diameter cellulose casings are produced in long lengths, but large diameter fibrous cellulose casings are manufactured separately. Fibrous casings, designed as special tough casings, are reinforced with cellulose fibres having great strength as well as many of the attributes of natural casings; they take print well. Special types of fibrous casings are the so-called easy-release and plastic-coated moisture-proof casings. Dry sausage fibrous casings are especially developed for semidry and dry sausages.
The interior surface of the cellulose casings can contain a water soluble dye which colours the sausage surface during heat processing. Coloured cellulose casings in cream, yellow, black and other colours are used for the cooked type of sausage. The stuffed sausages have a smooth surface and the nature of the casing offers hygienic protection for the sausage content.
Cellulose and other artificial casings are not as permeable to smoke as animal casings. Stuffed cellulose casings cannot be pricked to expel air unless a red hot needle is used. After the small casings are stuffed, they are twisted in the same way as natural casings but with large casings the open end is twisted and then tied. Cellulose casing for small diameter sausages should be peeled from the product by the sausage manufacturer.
Regenerated collagen casings have many advantages and may be edible or inedible. Edible collagen casings are stronger than natural casings. The inedible collagen casings must be removed from the product before consumption.
Many types of plastic casings are available today. They are usually impermeable to moisture and are sold under different names. The use of special grade smooth polyethylene casings is another development in sausage production. Polyethylene casings take print exceptionally well and permit an attractive presentation.
Impregnated cloth casings and other artificial casings are also used for stuffing sausages.
The meat emulsion is extruded through the stuffing horn into natural or synthetic casings mounted over the end of the stuffing horn.
Fig. 22 HAND LINKING OF SAUSAGES IS A SKILLFUL OPERATION
The large diameter casings are tied at one end, placed on the stuffing horn and the sausage emulsion is ejected through the horn. The machine operator has to hold the casing on the stuffing horn with one hand to restrict the flow off the horn while operating the clipping or tying machine with his other hand. For linking small diameter sausages 2 to 4 ply cotton thread is usually recommended while for tying very large diameter sausages 10 to 16 ply thread may be necessary.
Cellulose casings for large sausages are first tied or clipped dry, soaked prior to stuffing and then they are tied wet for the second closure. Fibrous casings are clipped wet or dry at both ends.