Text 1. By-products of the Meat Industry

Animal by-products include everything of economic value, other than the carcass, obtained from an animal during slaughter and processing. These products are classified as either being edible or inedible, based upon whether or not they are intended for human food.

The meat packing industry has long been noted for its efficiency in the processing and utilization of by-products. Over the past several years, the value of by-products has declined. This relative decline in value has been due largely to technological progress in producing competitive products from nonanimal sources. For example, various synthetic materials have been developed to make many items which were once made of leather. Synthetic fibers, instead of wool, are used to make clothing. In many food products, vegetable fats and oils have replaced animal fats. Synthetic detergents have replaced soaps, which were once made entirely from animal fats. Many other examples could be cited to illustrate the competition from nonanimal

products.

Enormous quantities of by-products are generated at each step of the meat processing and distribution system. Yields of by-products vary greatly, depending upon the method of processing and the weight, grade, sex and species of animal. The value of by-products is greater when these products are processed immediately after slaughter.

The number of edible by-products, and the extent to which these items are processed for edible uses, varies among processors. Unless the processor has a potential market for an item, it may not be economically feasible to process it for edible use. Without a potential market, it might become more profitable to process the item for an inedible use.

Beef extract is a very useful beef by-product. It consists of the concentrated cooking water from the heating of beef during the canning process. This liquid is usually concentrated by evaporation under vacuum to about a 20 percent moisture content, and set up, upon cooling, as a pasty solid. It is a major ingredient in bouillion cubes and bouillion type broth, and is used as a flavouring agent in gravies.

The testicles of lambs and calves are sold fresh or frozen. When cooked they are commonly known as “fries” or “mountain oysters”.

Blood is used as a component of blood sausages, and special hygienic precautions must be taken when it is collected for edible use. Recently, ultrafiltration processes have been used to recover proteins from both the plasma and cellular components of blood. These blood proteins have many potential uses as a binder material in sausage, and in the manufacture of other food products.

Chitterlings are made from the thoroughly cleaned and cooked intestines of the pig, and are sold as a variety meat.

Cheek and head trimmings are commonly used in the manufacture of various sausages.

Oxtails are used mainly for making soups.

 

Inedible Meat By-products

A list of some of the more important inedible by-products that are ob­tained from meat animals is presented in Table 16-4. The use of some of these processed by-products are varied, and are almost unlimited in number. New uses are continually being found for these products, while other nonmeat products are replacing existing meat by-products.

Tallows and Greases. Inedible fats are classified as tallow or grease mainly on the basis of their titer, which is the congealing or solidification point of the fatty acids in the fat. Any fat having a titer above 40°C is classed as a tallow. Fat with a titer below 40°C is classed as a grease. Most cattle and sheep fats are tallow; pork fat is classified as grease.

The sources of inedible tallows and greases include animals that die in transit, diseased and condemned animals and parts, and waste fat and trimmings from retail meat markets, hotels, and restaurants. How­ever, a large portion of the inedible fat produced by packinghouses comes from edible fats that had a potential market as such.

Most inedible fats are processed by the dry rendering process. The fatty tissues are ground and placed into a horizontal, steam-jacketed cylinder equipped with a set of internal rotating blades. Rendering may be accomplished at atmospheric pressure, at an elevated pressure, or under a partial vacuum. The fat cells are ruptured, and the melted fat isreleased from the supporting tissues. When sufficient moisture has cooked out, the mixture is filtered or strained to remove the cracklings from the rendered tallow or grease.

Many uses have been found for the products obtained from inedible tallows and greases. These fats can be split, by the action of acids or bases, into glycerine and fatty acids. Glycerine is used in the manu­facture of pharmaceuticals, explosives, cosmetics, transparent wrapping materials, paints, and many other products. Likewise, fatty acids have many industrial uses, such as in the manufacture of soaps and detergents, wetting agents, in insecticides and herbicides, cutting oils, paints, lub­ricants, and even as an additive to asphalt.

The mixed feed industry uses large quantities of stabilized inedible tallows and greases. Fats make feedstuffs less dusty, more palatable, and facilitates the pelleting process. They also add energy to the feed. Fats used in animal feeds are stabilized against rancidity by the addition of antioxidants, such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), during the chilling that follows the rendering process.

Animal Feeds and Fertilizers. Most large packing plants have facilities for rendering inedible materials produced during their slaughter operations. Independent rendering plants collect and process materials from slaughter and processing plants that do not have their own rendering facilities. The end products of the rendering operations are fats and proteinaceous materials. After they are separated from the fats, the proteinaceous materials are dried and ground. These protein concentrates are quite valuable, and are used as protein supplements in feeds for pigs, chickens, and pets.

The pet food industry has grown very rapidly, and uses large quan­tities of select meat by-products. Such items as liver, spleen, lung, meat meal, horse meat, and cereal products are used in making dry, semimoist, and canned cat and dog food.

Dried blood (blood meal) is made by coagulating fresh blood with steam, draining off the liquid, and drying the coagulum. This dried blood is a rich source of protein, and it is used as an ingredient in animal feeds. Blood meal is used rather extensively in the formulation of feed for commercial fish operations. Meat meal (proteinaceous materials from the inedible rendering process) and organs, such as liver, are also used for fish foods.

Steamed bone meal is made by cooking bones with steam, under a high pressure, in order to remove any fat and meat that may be left on them. The dried bone is then ground up and used as a calcium and phosphorus supplement in animal feeds.

The use of animal by-products in fertilizers is limited almost entirely to the manufacture of speciality fertilizers for home gardening use, which represents a very small proportion of fertilizer production.

Glue. Chemically and physically, glue and gelatin are very much alike. The raw materials from which glue is made include the skins or hides, connective tissues, cartilage, and bones of cattle and calves. Glue is extracted from these materials by successive heatings in water under specific temperature conditions. Cooking in water converts the collagen in these materials to gelatin. The extracts are concentrated, dried, and ground up. Glue has many and varied uses in the woodworking, paper, and textile industries, and its manufacture dates back more than 3000 years to the cabinet makers of Egypt. Blood albumen (obtained from blood plasma after the red cells have been removed) is now used to make an adhesive, almost all of which is used in manufacturing plywood and wood veneers.

Pharmaceuticals. The endocrine glands in the animal body secrete hormones that exert specific effects on the physiological functions of the body. These sub­stances, when extracted from the endocrine glands, have great value in treating disorders and diseases of both humans and animals.

Some of the endocrine glands are removed during the slaughter process, and are immediately chilled and frozen. The frozen glands are shipped to pharmaceutical plants where extraction, concentration, and purification processes are performed to prepare the final products for use in the medical profession.

 

Tissues and Organs

Blood. In addition to its industrial uses, blood yields many pharma­ceutical products. Purified bovine albumen is used as a reagent in testing for the presence of Rh factor in human blood, as a stabilizer for vaccines and other sensitive biological products, in antibiotic sensitivity tests, and in microbiological culture media. Blood is also a source for amino acids that are used in the intravenous feeding of hospital patients.

Bone. Purified bone meal is used as a source of calcium and phos­phorus in pediatric foods.

Intestines. The small intestine of sheep is made into surgical ligatures for suturing internal incisions or wounds. This product con­sists mainly of collagen which the enzymes of the body will subse­quently digest.

Liver. Liver extracts are used in treating pernicious anemia. How­ever, since vitamin B₁₂ was isolated from liver, and synthesized, the use of liver extract for the treatment of this anemia has declined. Bile extract, obtained from the bile of cattle, is used to increase the secretory activity of the liver. Bile extract can also be used to make cortisone, an adrenalcortical steroid hormone with anti-inflammatory properties similar to those of ACTH.

Lungs. Heparin is obtained from lungs or liver, and is used as an anticoagulant to prevent blood clots.

Spinal cord. The spinal cord from cattle is a source of cholesterol. The principal use of cholesterol is in the preparation of vitamin D.

Stomach. Rennet, from the stomach of calves, is used to curdle milk in the cheese making process. This enzyme can also be added to the diet of infants to aid in their digestion of milk. Mucin is obtained from pig stomachs, and is used in the treatment of ulcers. Pepsin is also obtained from pig stomachs, and was used at one time as an aid to digestion.

This list of preparations obtained from animal tissues, although in­complete, will serve to illustrate the importance of animals and the meat packing industry to our health and well-being.

 

Text 2. Cookery

The art of meat cookery exists because of the sharing of culinary ex­perience from generation to generation. Certain principles of meat preparation must be observed, in order to increase the likelihood of high palatability in the finished product. These principles include knowledge of the time and temperature com­binations that will assure the preparation of meat having the maximum eating satisfaction. Knowledge about various characteristics of a cut of meat and its probable response to heat is also vital to successful meat cookery.

Effects of Heat on Meat Constituents.

When the proteins of muscle are exposed to heat, they lose their native structure and undergo several changes in configuration. In general, denaturation of the protein occurs. This may be accompanied by an aggregation, of the protein molecules (coagulation), the presence of which indicates a loss in protein solubility.

The amount of protein solubility that is lost depends on the time and temperature of heating. These changes are measurable in terms of water holding capacity. High cooking temperatures reduce water holding capacity, and the duration of heating is im­portant at temperatures between 30-70°C. These changes occur in most of the proteins of the muscle fiber, upon heating..

The connective tissue protein elastin is not susceptible to the effects of heat. Even though properly cooked, some meat will have a persistent toughness because of a high elastin content. The only method of tenderizing such products is by use of the plant proteolytic enzymes.

Several other alterations occur when the muscle proteins are sub­jected to heat. These include changes in pH, reducing activity, ion binding properties, and enzyme activity.

Certain volatile materials are driven off during the heating of meat that contribute to the unique flavor and aroma of cooked meat. These include various sulfur and nitrogen containing compounds, as well as certain hydrocarbons, aldehydes, ketones, alcohols, and acids.

The process of fat translocation in cooked meat is brought about by raising the muscle temperature. The solubilization of collagenous connective tis­sue provides channels through which the melted fat may diffuse. Thus, the cooking action results in a movement, and possibly an emulsification, of the fat with soluble protein.

Effects of Heat that Are Associated With Palatability

Heat can cause both the tenderization and the toughening of meat. In general, those heat induced changes in proteins that result in coagula­tion and hardening, reduce tenderness. At the very low cooking temperature of 56-58°C, the tenderization is relatively slow. Upon raising the temperature slightly to 62-64°C, some improvement in tenderness occurs upon prolonged heating. At the higher temperature of 72-74°C, protein hardening and toughening occurs. However, continued heating at this temperature results in a substantial amount of gelatin formation and this change causes meat tenderization.

Practical guides to meat cookery can be developed on the basis of time and temperature influences on tenderness. For example, the un­necessary toughening of most cuts of meat can be avoided by preventing the internal temperature from rising to a level that causes protein hard­ening. However, it is necessary to cook some meats in this temperature range, in order to develop other desirable palatability characteristics. To achieve the best flavor development, and a complete conversion of pigment to the denatured (brownish-grey) form, the recommended end point for most fresh pork is 77°C, and for poultry is 77-82°C. Other meats, notably beef, are cooked to a degree that is consistent with the pref­erences of the consumer. Meat heated to an internal temperature of 58-60°C is considered rare; 66-68°C, medium rare; 73-75°C, medium; and 80-82°C, well done.

The end color of the cooked meat is a function of the combination of cooking times and temperatures.

The extent of heating is an important influence on con­sumer acceptability through its effect on the chemical state of the muscle pigments.

Severe cooking procedures that cause extensive dehydra­tion of the meat also render it less juicy to the consumer. Meat that con­tains 68-75 percent moisture in the raw state, will contain about 70, 65, and 60 percent moisture after being dry-heat roasted to 60, 70, and 80°C, respectively. The losses that occur are due to evaporation and drip losses. Of course, the extent of these losses also depends on the water holding capacity of the tissues.

Flavor development is an important result of the meat cooking pro­cess. The changes in the quantity and type of volatile materials that are present are extensive, but poorly understood. Yet, the effects of heat are so unique that the type and conditions of cookery often may be identi­fied solely by the flavor and aroma of the product. Dry heat cookery imparts certain flavors, particularly at the exposed surfaces where tem­peratures become very high. On the other hand, cooking with moisture under pressure causes the development of pronounced and unique flavor changes in the deep tissues of the cut.

Methods of Cookery.

There are several systems by which temperature increases are accom­plished in meat. Although the major objective in meat cookery is to achieve a particular internal temperature, the rate of heating, the equipment used, and many other factors influence the characteristics of the final product.

Of particular importance in determining the cooked character of meat is the amount of moisture present during heating. Since all meat contains water, there will be some moisture effects. Water is a good conductor of heat, and its presence aids in the penetration of heat into the deepest parts of the cut. On the other hand, the moist surfaces of meat can also delay the heating process, due to the evaporative cooling that takes place. Water is also necessary for developing the tenderness and final texture of cooked meat because of the hydrolysis of connective tissue that occurs.

One of the essentials for success in meat cookery is knowledge of the proper duration of heating. For thin cuts, such as steaks or chops, the criteria are subjective. The experienced cook can determine the proper end point from the color and rigidity of the cut. However, the proper cooking of very thick cuts, such as roasts, requires the use of a meat thermometer. The thermometer is inserted into the thickest part of the cut, avoiding pockets of fat and bones, so that the temperature in the coolest region will be detected. For thick cuts, this is the only method that will completely assure attaining the desired degree of doneness.

Dry heat cookery. Cooking with dry heat can be accomplished by any method that surrounds the cut of meat with hot dry air. Broiling and roasting are the best examples of dry heat cookery.

Broiling is appropriate only for tender cuts, such as steaks or chops, because the heating period is usually of rather short duration and there is inadequate time to achieve connective tissue breakdown. The high surface temperature results in the development of a unique flavor in the cut, and of an extensive browning on it. The duration of the heating is extremely critical, since the cuts are relatively thin and the tempera­tures used are quite high.

Charcoal broiling is a very popular method of cooking that also im­parts a unique flavor. Many products, such as chops, steaks, chicken, ribs, kabobs, sausage, or roasts, are cooked by this method. The tem­peratures used are usually lower than those of oven broiling. The prod­ucts acquire a pronounced smoked flavor from the combustion of the charcoal and the melted fat that drips on it.

Roasting with dry heat is appropriate for tender roasts. It is usually accomplished in an oven at temperatures of 150-175°C. It imparts unique flavor by the sugar-amine browning action. However, the cut should be protected during roasting by a layer of ex­ternal fat to prevent excessive moisture losses. If the cut is a large one, it is possible to use relatively low (120°C) oven temperatures for an extended period of cooking. The limited surface area per unit of meat in these large cuts prevents extensive moisture losses.

Moist heat cookery. If a meat cut contains a relatively large amount of connective tissue, it is desirable to provide extra water during cooking. This provides all the water that is necessary for the complete hydrolysis of collagen into gelatin. Low temperatures are prescribed, over a long cooking time, to allow this conversion to occur without hard­ening the myofibrillar proteins. It is emphasized that this action occurs in collagen, but does not occur in elastin. Thus, a cut that does not tenderize, in spite of extensive cooking, is probably high in elastin con­nective tissue fibers. Braising, cooking in water, or pot roasting are examples of moist heat cookery. The heating is accomplished in a closed container with added water. Seasoning, sauces, or flour may also be added to enhance the development of a desired flavor and texture in the final product. The tenderizing action in moist heat cookery may be achieved by wrapping cuts in moisture proof materials and heating them in a dry oven. The natural juices are trapped and moisture loss is minimized. Consequently, the heating may be extended for long periods of time to allow the collagen to change into gelatin. The heating temperatures are usually in the range of 95-100°C for this method.

Microwave cookery. The use of microwaves for heating meat represents a modern method of cookery that is extremely rapid. The heating results from the conversion of microwave energy to heat by friction from internal molecular rotations caused by the interactions of molecules with the rapidly fluctuating electromagnetic field. Frequen­cies of 915 and 2450 megahertz (millions of cycles per second) have been approved for such purposes. This method permits meat cookery that is many times faster than conventional methods, al­though some variation exists in doneness and textural properties. Some of these are alleviated when external heating coils are used to brown the outer surface of the meat, while the interior is being cooked by the microwave radiation. Its utilization by the food service industry repre­sents the most widespread application to meat cookery. However, it is also gaining popularity as a cooking method in the home.

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