Meat Processing Operations

Beef Processing
Pork Processing
Poultry Processing
Fish Processing
Rendering Process

Beef Processing Description 

Pork Processing Description 

Approximately 100 million hogs are processed annually in the United States. The live weight of swine slaughtered for meat production averages 250 pounds per animal. Up to 70 percent of the pig carcass can be used, which is greater than other farm animal species. This high recovery rate is due to the fact that a hog has one stomach (where a cow has four) and is dressed with the feet and skin intact instead of removed. However, some processors remove the feet before processing. Additionally, the portion of edible components is higher than that of cattle. The diagram following this section illustrates the flow of pork processing.

Animal Pre-handling: Swine are delivered to the processing plant from the market or farm and placed in holding yards for one to two days. They are generally made to fast for a day to reduce intestinal contents. Most processors schedule receipt from producers of the live animals for slaughter to provide a continuous supply of animals for processing. Live animals are received from the supplier at the meat plant and are placed in holding areas where they are rested for typically one day before slaughter. This practice eliminates the need for feeding and reduces manure accumulation in the holding pens. Water is provided to minimize weight loss.

The holding areas should have adequate facilities for livestock inspection including walkways over pens, crushes and other containment structures. These areas may be covered or totally enclosed to provide some protection from weather conditions and primarily to reduce runoff from precipitation events. Water pollutant concentrations from this activity depend on whether the pens are scraped (dry cleaned) prior to washing with water. Sick animals and those unfit for human consumption are identified and removed from the normal processing flow. Processors should have separate isolation and holding pens for the unhealthy animals. The pigs are weighed prior to processing so the yield can be accurately determined.

Stunning and Bleeding: Hogs must be rendered completely unconscious prior to being shackled and hoisted for exsanguination (bleeding). Stunning must be conducted with a federally acceptable device (mechanical, chemical or electrical) and is typically done by electric shock or anesthetization using carbon dioxide. In large commercial operations, a series of chutes and restrainer conveyors move the animals into position for stunning. Once unconscious, the animals are bled, usually with a hollow knife that directs the blood to a collection trough. The blood is then pumped to an agitated tank for further processing.

Dehairing and Finishing: Before further processing, hair is removed from the carcasses by scalding in hot water followed by scraping. Carcasses are then singed to take out any remaining hair. In large operations, the carcasses are transported through a scalding tub by an automated conveyor moving at a calibrated speed to ensure proper scalding times. In these automated systems, the carcasses are continually moved and turned for uniform scalding. In small plants without automation, hair condition is checked periodically during the scalding period. Some processors also remove hair by passing the carcass through gas flames to singe the hair. Rotating brushes remove the remaining hair, then the carcasses are scraped a final time and thoroughly washed from the hind feet to the head.

Some processors skin the hogs after exsanguination. The head and belly of the carcass are hand-skinned and the legs are either hand-skinned or removed. The pigskins are trimmed, salted, folded and stored in 50-gallon drums.

Evisceration and Splitting: After dehairing and hide finishing, the carcasses are eviscerated to remove the abdominal organs. All of the internal organs are inspected, and those intended for human consumption are separated and the remainder discarded into a rendering barrel. After evisceration, the heads are separated and the carcasses split in half. The carcass is washed from the top down to remove any bone dust, blood or bacterial contamination. After sanitizing, the carcass is inspected a final time and the inspection stamp applied to the wholesale cut.

Chilling: Inspected carcasses are placed in coolers at 0-1?C (32-34?F) with air velocity typically at 5-15 mph for a 24-hour chill time. For thorough chilling, the internal ham temperature should be at least 3?C or 37?F. Spray chilling is permitted by the USDA to reduce cooler shrink. Spray solutions may contain chlorine, which acts as a sanitizer. Some carcasses are sent directly to a freezer, which reduces shrinkage. After adequate chilling has occurred, cutting and boning is performed.

Cleaning: Federal and state regulations require equipment and facilities used for processing of live animals for human consumption be completely cleaned at least every eight hours of operation to maintain sanitary conditions. The daily schedule for meat processors consists of one or two eight-hour production shifts followed by a six  to eight-hour cleaning period.  For a typical cleanup procedure, equipment, walls and floor surfaces are initially rinsed with water to remove loose solids. The surfaces are then scrubbed with detergents and sanitizers and rerinsed. 

Byproduct Processing: Edible offal and casings (intestinal tract) are separated from the viscera and sent for cleaning and further processing. At various stages in processing, inedible materials such as bone, fat, heads, hair and condemned offal are generated. These materials are sent to a rendering plant for processing into feed and tallow. See the Rendering Process Description for further information.

Specific information on meat processing wastes is contained in the Environmental Impacts Section.

Poultry Processing Description 

More than seven billion birds are processed annually in the United States (USDA), with daily averages of 20,000 at individual plants. Poultry slaughtering consists of hanging, stunning, bleeding, scalding, defeathering, picking and washing. The diagram following this section illustrates the flow of poultry processing.

Receiving and Hanging: Birds are transported to the processing plant with the delivery scheduled so the poultry is processed on the day of receipt. Birds are not fed for one to four hours before slaughter to ensure their crops are empty for cleaner production. Live birds are delivered by truck from the supplier in cages where they are unloaded onto a dock area. The live bird holding areas are usually covered and have cooling fans to reduce bird weight loss and mortality during hot weather conditions (Sams, 2001). Birds are removed from the cages and then transported by conveyor to the live hang area inside the processing plant. The empty crates are returned to a wash area where they are cleaned and disinfected before leaving the facility. Washing and sanitizing of cages and trucks is common in turkey processing but not in the broiler chicken industry (USEPA, 1975).

Employees lift live poultry from the supply conveyer and hang the birds by their feet from a shackle conveyor. For the best poultry quality, the live birds should not be stressed prior to slaughter. Thus, noise and light are kept to a minimum in the hang room. Many processors use red lights in the hanging room so that employees can see but birds cannot.

Bleeding and Defeathering: From the hang room, the birds are conveyed to the kill room. Upon arrival, the birds are lowered into an electric water vat where they are anesthetized. A machine usually equipped with a circular saw blade then cuts the throats. Bleeding may take 1-3 minutes but must be complete to produce the desirable white or yellow skin color in the final dressed bird.

The birds enter a hot water scald tank with troughs and flumes to keep them totally submerged. Scalding loosens the feathers and makes for easier plucking and fine feather removal. Scalding temperatures and times vary from 123?F to140?F and from 30 to 90 seconds. The higher temperatures require shorter scald times; however, elevated temperatures may result in removal of portions of the skin. Optimum conditions should be established for the type of bird being dressed. The FDA requires a minimum of one quart of hot water be used per bird for feather removal; however, many processors use much more.

Additional defeathering is performed by a mechanical device with rotating rubber fingers that beat and rub the feathers away from the carcass. Water washes away the feathers and acts as a lubricant. Carcasses are then singed for final hair and feather removal. The defeathered birds are washed with water and scrubbed with mechanical rubber fingers. Blood and feathers are collected and sent to rendering either on- or off-site for transformation into byproduct meal.

Evisceration and Inspection: The carcasses are removed from the kill line by cutting off the feet and rehanging on shackles in the evisceration line. A mechanical arm removes the internal organs of the bird. Each bird is inspected for signs of disease and the viscera from the body cavity is also presented for USDA inspection. The giblets (hearts, livers and gizzards) are removed and further processed. The remaining organs are sent to offal or waste. The giblets are trimmed and washed, packed in a giblet bag, and returned to the body cavity. The whole bird is removed from the conveyor, weighed and classified. (Chlorination for Poultry and Meat Processing, Severn Trent Services, Capitol Controls, 2000)

Cutting and Deboning: After a chicken has been eviscerated and cleaned, it is either prepared for packaging as a whole bird or sent through additional cutting and deboning steps. The cutting only prepares a bone-in product, while the cutting and deboning produce boneless cuts. In the cutting process, the wings and legs/thighs are removed from the carcass and the back is cut away from the breast. Bones are not removed. At this point parts can be packaged as a consumer product, bulk-packed for delivery to other processors, or shipped for further processing into a variety of products, including breaded or marinated goods. For additional information on further processing for poultry, refer to 4.5.2 Poultry Further Processing Operations, EPA's Meat and Poultry Products Industry Overview.

Within-plant processing of cut-up parts generally involves creating a boneless product. Deboning involves cutting meat away from the bone with knives, and trimming and cleaning with bladed knives or scissors. The deboned parts are generally packaged as a fresh or flash-frozen consumer product.

Chilling: Birds passing inspection are thoroughly washed inside and out and then rapidly chilled at 30-35?F to preserve quality and prevent spoilage. Chilling is performed with cold water or ice slush. The birds absorb small amounts of moisture and are sized and graded for quality. The FDA requires a chilled water flow rate of about two gallons per bird.

Packaging: No matter how a bird is packaged, it is almost always placed in a large cardboard box for shipping. Packaging is necessary to get the processed product from the plant to the consumer. The graded poultry is packaged fresh in boxes containing crushed ice. Birds must be kept below 40?F and quickly transported to retail distributors since the product's shelf-life may be only a few days. Poultry is often frozen to prolong storage life. The birds are vacuum-packed in low-moisture and low oxygen transmission bags or films, since the chicken fat is highly susceptible to microorganism growth.

Specific information on poultry processing wastes is contained in the Environmental Impacts Section.

Fish Processing Description 

The fish and shellfish processing industry includes marketing of fish, shellfish and marine plant and animals as well as byproducts such as fish meal and oil. Fish meal is used as a livestock feed and the oil is used in margarine and paints. Fish canning and byproduct manufacturing are conducted at 136 plants in the United States. Exports of canned fish and fish meal are increasing due to the diminishing supply in other countries. About 30 percent of fish processed for human consumption is marketed as fresh; the remainder is frozen fish and filets in ready-to-eat meals and other convenience products.

Fish processing most commonly occurs at onshore facilities; however, some takes place at sea or aboard fishing vessels. This description covers on-shore operations. Additionally, some industry sectors operate seasonally. Salmon processing typically occurs less than 100 days of the year during the harvesting season with plants operating at full capacity.

The diagram following this section illustrates the flow of seafood processing.

Pretreatment: Fish are kept on ice in boxes before delivery to the processing plant. Upon arrival, the fish may be re-iced and placed in cold storage until required for further processing. Pretreatment involves ice removal, washing, grading according to size and de-heading. Large fish may also be scaled before additional processing. Some fish such as mackerel are skinned by immersing into a warm caustic bath. The effluent from this process has a high organic load and has to be neutralized before discharge.

Filleting: The filleting areas are generally separated from the pretreatment department to prevent workers and materials from the nonsterile pretreatment from contaminating the sterile filleting area. Filleting is performed by machines with mechanical knives that cut the fillets from the backbone and remove the collarbone. Some fillets may be skinned at this step in the process.

Trimming and Inspection: In the trimming department, pin bones are removed and operators inspect the fillets. Any defects and any inferior parts are removed. Offcuts are collected and minced. Depending upon the final product, the fillets can be cut into portions according to weight or final product requirements. The fillets are inspected to ensure they meet product standards.

Fresh Packaging/Storage: Fresh products are packaged in boxes with ice which is separated from the product by a layer of plastic. Fillets or pieces can be individually frozen and wrapped in plastic. The most common method is packaging in 12-25 lb blocks in waxed cartons. The blocks are typically frozen and kept in cold storage.

Canning: Canning is performed by two methods: precooking and raw pack. Precooking begins with thawing of the fish which are then eviscerated, washed and cooked. Cooking occurs with steam, oil, hot air or smoke for up to 10 hours, depending upon the fish size. The cooked fish are then cooled. Refrigeration may be used to reduce cooling time. After cooling, the head, fins, bones and undesirable meat are removed and the remainder is cut/chopped and placed in cans. Oil, brine and/or water are added to the cans which are sealed and pressure-cooked before shipment.

The raw pack method begins with thawing and weighing of the fish. They are then washed and possibly brined as well as "nobbed," which is the removal of the head, viscera and tails. The fish are placed in cans, then cooked, drained and dried. After drying, liquid (oil, brine, water, sauce) is added to the cans. Finally, the cans are sealed, washed and sterilized with steam or hot water and then stored.

Fish Meal and Oil Production: Most large canneries also operate a fish meal plant, where the fish not suitable for canning are combined with offal and processed into fish meal. Fish meal is derived from the dry components of the fish and the oil from the oily component. The water that makes up the remainder of the fish matter is evaporated during the process. Most fish meal and oil production processes are automated and continuous. Production rates vary according to season and types of fish being processed.

The fish byproducts are cooked in a process that coagulates the protein and releases the water and oil. The mixture is screened and the liquid from the mixture is squeezed out through a perforated casing. The pressed cake is shredded and dried with steam or direct flame dryers. The meal passes through a vibrating screen and to a hammer mill where it is ground to the desired size. The ground meal is automatically weighed and bagged. The meal is used in animal and pet feed due to its high protein content.

The oil is further processed by passing through a decanter to remove sludge which is then fed back into the meal dryer. Oil is separated from the liquid by centrifuge and is "polished" by using hot water washes and additional centrifuging. The removed water is evaporated to concentrate the solids and the remaining oil is refined to remove any impurities. See the Rendering Process Description for additional information on byproduct manufacturing. Discussion of wastes generated from meat and fish processing is included in the Environmental Impacts section. 

Rendering Process Description 

Having commercial value, meat byproducts contribute significantly to the profits of slaughter operations. The United States produces an average seven million tons of rendered products annually with a value of $3 billion. Use of byproducts also reduces the overall environmental impacts of processing operations. Rendering converts meat, poultry and fish byproducts into marketable goods for agricultural and industrial use. Materials include viscera, meat scraps, bone, blood, feathers and dead animals.

Rendering involves cooking, separating and drying processes where edible (fit for human consumption) and inedible (not suitable for human consumption) animal derivatives are made into useful commodities. Edible rendering facilities process fatty animal tissue into edible fats and proteins. The inedible rendering plants produce tallow and grease, which are used in livestock and poultry feed, soap and production of fatty acids. Currently, an estimated 150 independent, off-site rendering facilities and 100 integrated plants (rendering on-site at processing plant) are operating in the United States. The independent renderers gather raw materials from small slaughterhouses, supermarkets and butcher shops where the on-site processors receive offal and other goods directly from plant operations.

Edible Rendering: The diagram following this section illustrates the flow of edible byproduct processing. Animal byproducts are chopped or ground into small pieces then cooked. As the material is heated, moisture and fats are released. The proteinaceous solids are separated from the melted fat and water by a centrifuge. The edible fat is then separated from the water with additional centrifuging. The water is discharged as sludge and the fat is pumped to storage.

Inedible Rendering: The diagram following this section illustrates the flow of inedible byproduct processing. Inedible rendering is performed by wet or dry processing. Wet methods separate the fat from the raw materials by boiling in water. Water and live steam are used to cook the raw substances for fat separation. Dry rendering is a batch or continuous process that dehydrates the matter to release the fat. Following dehydration, the melted fat and protein solids are separated. At present, only dry rendering is used in the United States. Wet rendering is no longer used due to its high energy consumption and related costs and adverse effects on the fat quality.

In batch rendering of nonedible foodstuffs, multiple cookers are used. Raw material is crushed to 1-2 inches diameter and cooked. The final contents are screened and pressed to separate the fats from the protein solids. The solids, called "cracklings," are ground to produce protein meal. The fat is centrifuged or filtered to remove any remaining protein solids and is then stored in a tank.

Since the 1960s, continuous rendering systems have been installed to replace batch systems at some plants. This system is similar to the batch configuration except that a single, continuous cooker is used rather than several parallel batch cookers. Continuous cookers cook the material faster than batch cookers and usually produce a higher quality of fat. From the cooker, the material is filtered to remove any solids and the fat is placed in an animal fat storage tank.

Inedible Products Processing: Blood processing and drying is an auxiliary process in meat rendering operations. Whole blood from animal slaughterhouses is used to recover protein as blood meal, which is a valuable ingredient in animal feed due to its high lysine content. Poultry feathers and hog hair are rendered to convert keratin into amino acids. Restaurant grease is also used as another raw feed material.

Many of the byproducts from meat processing can be processed further into value added products. For example, pet food from viscera, gelatin from head pieces, meat meal from hoofs, chicken parts, bone and horn, glue from hides and blood meal and small goods from blood like adhesives. Significant environmental gains can be achieved from maximizing the utilization of these materials so that they become a resource rather than a waste.

The efficient recovery and segregation of blood is an important means of reducing the pollution loads in wastewaters, since blood is a highly polluting substance. An operation with an efficient blood recovery system will have a 40 percent lower polluting load than one that allows blood to flow to the wastewater stream (Nielsen, 1989).