Tuesday, 29 March 2011 19:17

Dairy Products Industry

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Dairy products have formed an important element in human food since the earliest days when animals were first domesticated. Originally the work was done within the home or farm, and even now much is produced in small-scale enterprises, although in many countries large-scale industries are common. Cooperatives have been of great importance in the development of the industry and the improvement of its products.

In many countries, there are strict regulations governing the preparation of dairy products—for example, a requirement that all liquids be pasteurized. In most dairies, milk is pasteurized; sometimes it is sterilized or homogenized. Safe, high-quality dairy products are the goal of manufacturing plants today. While recent advances in technology allow for more sophistication and automation, safety is still a concern.

Liquid or fluid milk is the basic raw material for the dairy products industry. The milk is received via tanker trucks (or sometimes in cans) and is unloaded. Each tanker is checked for drug residues and temperature. The milk is filtered and stored in tanks/silos. Temperature of the milk should be less than 7 °C and held for no more than 72 hours. After storage, the milk is separated, the raw cream is stored in house or shipped elsewhere and the remaining milk is pasteurized. The raw cream temperature should also be less than 7 °C and held for no more than 72 hours. Before or after pasteurization (heating to 72°C for 15 seconds), vitamins may be added. If vitamins are added, proper concentrations must be administered. After pasteurization, the milk goes into a storage tank. The milk is then packaged, refrigerated and entered into distribution.

In the production of cheddar cheese, the incoming raw milk is filtered, stored, and the cream separated as discussed above. Before pasteurization, the dry and non-dairy ingredients are blended with the milk. This blended product is then pasteurized at a temperature greater than 72 °C for over 15 seconds. After pasteurization, the starter media (which has also been pasteurized) is added. The cheese-milk mixture then enters the cheese vat. At this time colour, salt (NaCl), rennet and calcium chloride (CaCl2) may be added. The cheese then enters the drain table. Salt may also be added at this time. Whey is then expelled and put into a storage tank. A metal detector can be used prior to filling to detect any metal fragments present in the cheese. After filling, the cheese is pressed, packaged, stored and entered into the distribution chain.

For the formation of butter, the raw cream from milk separation is either stored in house or received via trucks or cans. The raw cream is pasteurized at temperatures over 85 °C for over 25 seconds and placed in storage tanks. The cream is pre-heated and pumped into the churn. During churning, water, colour, salt and/or starter distillate may be added. After churning, the buttermilk that is produced is stored in tanks. The butter is pumped into a silo and subsequently packaged. A metal detector may be used prior to or after packaging to detect any metal fragments present in the butter. After packaging, the butter is palletized, stored and entered into the distribution chain.

In the production of dry milk, the raw milk is received, filtered and stored as previously discussed. After storage, the milk is preheated and separated. The raw cream is stored in house or shipped elsewhere. The remaining milk is pasteurized. The temperature of the raw cream and raw skim should be less than 7 °C and held for no more than 72 hours. The raw skim milk is pasteurized at a temperature over 72 °C for 15 seconds, evaporated by drying between heated cylinders or by spray drying and stored in tanks. After storage, the product enters a drying system. After drying, the product is cooled. Both the heated and cool air used must be filtered. After cooling, the product enters a bulk storage tank, is sifted and packaged. A magnet may be used prior to packaging to detect any ferrous metal fragments greater than 0.5 mm in the dry milk. A metal detector may be used prior to or after packaging. After packaging, the dry milk is stored and shipped.

Good Manufacturing Practices

Good manufacturing practices (GMPs) are guidelines to assist in the day-to-day operation of a dairy plant and to ensure the manufacture of a safe dairy product. Areas covered include premises, receiving/storage, equipment performance and maintenance, personnel training programmes, sanitation and recall programmes.

Microbiological, physical and chemical contamination of dairy products is a major industry concern. Microbiological hazards include Brucella, Clostridium botulinum, Listeria monocytogenes, hepatitis A and E, salmonella, Escherichia coli 0157:H7, Bacillus cereus, Staphylococcus aureus and parasites. Physical hazards include metal, glass, insects, dirt, wood, plastic and personal effects. Chemical hazards include natural toxins, metals, drug residues, food additives and inadvertent chemicals. As a result, dairies do extensive drug, microbiological and other testing to ensure product purity. Steam and chemical cleaning of equipment is necessary to maintain sanitary conditions.

Hazards and Their Prevention

Safety hazards include slips and falls caused by wet or soapy floor and ladder surfaces; exposures to unguarded machinery such as pinch points, conveyors, packing machines, fillers, slicers and so forth; and exposure to electrical shock, especially in wet areas.

Aisles should be kept clear. Spilled materials should be cleaned immediately. Floors should be covered with non-slip material. Machinery should be adequately guarded and properly grounded, and ground fault circuit interrupters should be installed in wet areas. Proper lockout/tagout procedures are necessary to ensure that the possibility of unexpected start-up of machines and equipment will not cause injury to plant personnel.

Thermal burns can occur from steam lines and steam cleaning and from leaks or line breaks of high-pressure hydraulic equipment. Cryogenic “burns” can occur from exposure to liquid ammonia refrigerant. Good maintenance, spill and leak procedures and training can minimize the risk of burns.

Fires and explosions. Leaking ammonia systems (the lower explosive limit for ammonia is 16%; the upper explosive limit is 25%), dry milk powder and other flammable and combustible materials, welding and leaking high-pressure hydraulic equipment can all result in fires or explosions. An ammonia leak detector should be installed in areas with ammonia refrigeration systems. Flammable and combustible materials must be stored in closed metal receptacles. Spraying of milk powder should meet appropriate explosion-proof requirements. Only authorized personnel should perform welding. Compressed-gas cylinders should be regularly examined. Precautions should be taken to prevent the mixture of oxygen with flammable gases. Cylinders should be kept away from sources of heat.

Frostbite and cold stress can occur from exposure in the freezers and coolers. Adequate protective clothing, job rotation to warmer areas, warm lunchrooms and provision of hot drinks are recommended precautions.

Exposures to high noise levels can occur in processing, packaging, grinding and plastic model blow-moulding operations. Precautions include isolation of noisy equipment, proper maintenance, wearing of hearing protectors and a hearing conservation programme.

When entering confined spaces—for example, when entering sewer pits or cleaning tanks—ventilation must be provided. The area should be free from equipment, product, gas and personnel. Impellers, agitators and other equipment should be locked out.

Lifting of raw materials, pulling cases of product and packaging of products are associated with ergonomic problems. Solutions include mechanization and automation of manual operations.

A wide variety of chemical exposures can occur in the dairy products industry, including exposure to:

  • ammonia vapours due to leaks in ammonia refrigeration systems
  • corrosive chemicals (e.g., phosphoric acid used in the manufacture of cottage cheese, cleaning compounds, battery acids and so on)
  • chlorine gas generated by inadvertent mixing of chlorinated sanitizer with acids
  • hydrogen peroxide generated during ultra-high-temperature packaging operations
  • ozone (and ultraviolet) exposure from UV light used in sanitizing operations
  • carbon monoxide generated by the action of caustics reacting with milk sugar in clean-in-place (CIP) operations in milk evaporators
  • carbon monoxide generated from propane or gasoline lift trucks, gas-fired heaters or gas-fired carton heat sealers
  • chromium, nickel and other welding fumes and gases.


Employees should be trained and aware of handling practices for hazardous chemicals. Chemicals must be labelled properly. Standard operating procedures should be established and followed when cleaning up spills. LEV should be provided where necessary. Protective clothing, safety goggles, face shields, gloves and so on must be available for use and subsequently maintained. An eye wash facility and a quick drench shower should be accessible when working with corrosive materials.

Biological hazards. Employees may be exposed to a variety of bacteria and other microbiological hazards from the unprocessed raw milk and cheeses. Precautions include proper gloves, good personal hygiene and adequate sanitary facilities.



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Food Industry References

Bureau of Labor Statistics (BLS). 1991. Occupational Injuries and Illnesses in the United States by Industry, 1989. Washington, DC: BLS.

Caisse nationale d’assurance maladie des travailleurs salariés. 1990. Statistiques nationales d’accidents du travail. Paris: Caisse Nationale d’assurance maladie des Travailleurs Salariés.

Hetrick, RL. 1994. Why did employment expand in poultry processing plants? Monthly Labor Review 117(6):31.

Linder, M. 1996. I gave my employer a chicken that had no bone: Joint firm-state responsibility for line-speed-related occupational injuries. Case Western Reserve Law Review 46:90.

Merlo, CA and WW Rose. 1992. Alternative methods for disposal/utilization of organic by-products—From the literature”. In Proceedings of the 1992 Food Industry Environmental Conference. Atlanta, GA: Georgia Tech Research Institute.

National Institute for Occupational Safety and Health (NIOSH). 1990. Health Hazard Evaluation Report: Perdue Farms, Inc. HETA 89-307-2009. Cincinnati, OH: NIOSH.

Sanderson, WT, A Weber, and A Echt. 1995. Case reports: Epidemic eye and upper respiratory irritation in poultry processing plants. Appl Occup Environ Hyg 10(1): 43-49.

Tomoda, S. 1993. Occupational Safety and Health in the Food and Drink Industries. Sectoral Activities Programme Working Paper. Geneva: ILO.