Dairy products workers handle machines that process milk, manufacture dairy products, and prepare the products for shipping. Workers are usually classified by the machine they operate. Workers at some plants handle more than one type of machine. Whole milk is delivered to a dairy processing plant from farms in large containers or in special tank trucks. The milk is stored in large vats until dairy processing equipment operators are ready to use it. First, the operator connects the vats to processing equipment with pipes, assembling whatever valves, bowls, plates, disks, impeller shafts, and other parts are needed to prepare the equipment for operation. Then the operator turns valves to pump a sterilizing solution and rinse water throughout the pipes and equipment. While keeping an eye on temperature and pressure gauges, the operator opens other valves to pump the whole milk into a centrifuge where it is spun at high speed to separate the cream from the skim milk. The milk is also pumped through a homogenizer to produce a specified emulsion (consistency that results from the distribution of fat through the milk) and, last, through a filter to remove any sediment. All this is done through continuous-flow machines.
The next step for the equipment operator is pasteurization, or the killing of bacteria in the milk. The milk is heated by pumping steam or hot water through pipes in the pasteurization equipment. When it has been at the specified temperature for the correct length of time, a refrigerant is pumped through refrigerator coils in the equipment, which quickly brings the milk temperature down. Once the milk has been pasteurized, it is either bottled in glass, paper, or plastic containers, or it is pumped to other storage tanks for further processing. The dairy processing equipment operator may also add to the milk specified amounts of liquid or powdered ingredients, such as vitamins, lactic culture, stabilizer, or neutralizer, to make products such as buttermilk, yogurt, chocolate milk, or ice cream. The batch of milk is tested for acidity at various stages of this process, and each time the operator records the time, temperature, pressure, and volume readings for the milk. The operator may clean the equipment before processing the next batch of whole milk.
Processed milk includes a lot of nonfat dry milk, which is far easier to ship and store than fresh milk. Dry milk is produced in a gas-fired drier tended by a drier operator. The drier operator first turns on the equipment's drier mechanism, vacuum pump, and circulating fan and adjusts the flow controls. Once the proper drier temperature is reached, a pump sprays liquid milk into the heated vacuum chamber where milk droplets dry to powder and fall to the bottom of the chamber. The drier operator tests the dried powder for the proper moisture content and the chamber walls for burnt scale, which indicates excessive temperatures and appears as undesirable sediment when the milk is reconstituted. Milk-powder grinders operate equipment that mills and sifts the milk powder, ensuring a uniform texture.
For centuries, butter was made by hand in butter churns in which cream was agitated with a plunger until pieces of butter congealed and separated from the milk. Modern butter-making machines perform the same basic operation on a much larger scale. After sterilizing the machine, the butter maker starts a pump that admits a measured amount of pasteurized cream into the churn. The butter maker activates the churn and, as the cream is agitated by paddles, monitors the gradual separation of the butter from the milk. Once the process is complete, the milk is pumped out and stored, and the butter is sprayed with chlorinated water to remove excess remaining milk. With a testing apparatus, the butter maker determines the butter's moisture and salt content and adjusts the consistency by adding or removing water. Finally, the butter maker examines the color and smells and tastes the butter to grade it according to predetermined standards.
In addition to the churn method, butter can also be produced by a chilling method. In this process, the butter maker pasteurizes and separates cream to obtain butter oil. The butter oil is tested in a standardizing vat for its levels of butterfat, moisture, salt content, and acidity. The butter maker adds appropriate amounts of water, alkali, and coloring to the butter oil and starts an agitator to mix the ingredients. The resulting mix is chilled in a vat at a specified temperature until it congeals into butter.
Cheesemakers cook milk and other ingredients according to formulas to make cheese. The cheesemaker first fills a cooking vat with milk of a prescribed butterfat content, heats the milk to a specified temperature, and dumps in measured amounts of dye and starter culture. The mixture is agitated and tested for acidity, which affects the rate at which enzymes coagulate milk proteins and produce cheese. When a certain level of acidity has been reached, the cheesemaker adds a measured amount of rennet, a substance containing milk-curdling enzymes. The milk is left alone to coagulate into curd, the thick, protein-rich part of milk used to make cheese. The cheesemaker later releases the whey, the watery portion of the milk, by pulling curd knives through the curd or using a hand scoop. Then the curd is agitated in the vat and cooked for a period of time, with the cheesemaker squeezing and stretching samples of curd by hand and adjusting the cooking time to achieve the desired firmness or texture. Once this is done, the cheesemaker or a cheesemaker helper drains the whey from the curd, adds ingredients such as seasonings, and then molds, packs, cuts, piles, mills, and presses the curd into specified shapes. To make certain types of cheese, the curd may be immersed in brine, rolled in dry salt, pierced or smeared with a culture solution to develop mold growth, or placed on shelves to be cured. Later, the cheesemaker samples the cheese for its taste, smell, look, and feel. Sampling and grading is also done by cheese graders, experts in cheeses who are required to have a state or federal license.
The distinctive qualities of various kinds of cheeses depend on a number of factors, including the kind and condition of the milk, the cheesemaking process, and the method and duration of curing. For example, cottage cheese is made by the method described above. However, the cottage cheese maker starts the temperature low and slowly increases it. When the curd reaches the proper consistency, the cottage cheese maker stops the cooking process and drains off the whey. This method accounts for cottage cheese's loose consistency. Cottage cheese and other soft cheeses are not cured like hard cheeses and are meant for immediate consumption.
Processed cheese products are made by blending and cooking different cheeses, cheese curd, or other ingredients such as cream, vegetable shortening, sodium citrate, and disodium phosphate. The processed cheese cooker dumps the various ingredients into a vat and cooks them at a prescribed temperature. When the mixture reaches a certain consistency, the cooker pulls a lever to drain the cheese into a hopper or bucket. The processed cheese may be pumped through a machine that makes its texture finer. Unheated cheese or curd may be mixed with other ingredients to make cold pack cheese or cream cheese. Other cheese workers include casting-machine operators, who tend the machines that form, cool, and cut the processed cheese into slices of a specified size and weight, and grated-cheese makers, who handle the grinding, drying, and cooling equipment that makes grated cheese.
Ice cream is usually made from milk fat, nonfat milk solids, sweeteners, stabilizer (usually gelatin), and flavorings such as syrup, nuts, and fruit. Ice cream can be made in individual batches by batch freezers or in continuous-mix equipment by freezer operators. In the second method, the freezer operator measures the dry and liquid ingredients, such as the milk, coloring, flavoring, or fruit puree, and dumps them into the flavor vat. The mix is blended, pumped into freezer barrels, and injected with air. In the freezer barrel, the mix is agitated and scraped from the freezer walls while it slowly hardens. The operator then releases the ice cream through a valve outlet that may inject flavored syrup for rippled ice cream. The ice cream is transferred to a filling machine that pumps it into cartons, cones, cups, or molds for pies, rolls, and tarts. Other workers may process the ice cream into its various types, such as cones, varicolored packs, and special shapes. These workers include decorators, novelty makers, flavor room workers, and sandwich-machine operators.
Newly hired inexperienced workers in a dairy processing plant may start out as dairy helpers, cheesemaker helpers, or cheese making laborers. Beginning workers may do any of a wide variety of support tasks, such as scrubbing and sterilizing bottles and equipment, attaching pipes and fittings to machines, packing cartons, weighing containers, and moving stock. If they prove to be reliable, workers may be given more responsibility and assigned tasks such as filling tanks with milk or ingredients, examining canned milk for dirt or odor, monitoring machinery, cutting and wrapping butter and cheese, or filling cartons or bags with powdered milk. In time, workers may be trained to operate and repair any of the specialized processing machines found in the factory.
The raw milk at a dairy processing plant is supplied by dairy farmers, who raise and tend milk-producing livestock, usually cows. Dairy farmers often own their own farms, breed their own cows, and use special equipment to milk the cows, often twice a day. Many also perform other farm-related tasks, including growing crops. Assisting the dairy farmer is the dairy herd supervisor, who takes milk samples from cows and tests the milk samples for information such as the amount of fat, protein, and other solids present in the milk. The dairy herd supervisor helps the farmer make certain that each cow in the herd is healthy and that the milk it produces will be fit for human consumption. Dairy herd supervisors do not generally work for one dairy farmer, but rather oversee the milk production at a number of farms.
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