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A dairy is a facility for the extraction and processing of animal milk (mostly from cows, sometimes from buffalo, sheep or goats) and other farm animals, for human consumption. A dairy farm produces milk and a dairy factory processes it into a variety of dairy products.
(In New Zealand English the word "dairy" means a corner shop, and "dairy factory" is the term for what is elsewhere a dairy).
History
People milked cows by hand, in some countries small numbers of cows are still milked by hand. Hand-milking is accomplished by grasping the teats (tits) in the hand and expressing milk by either squeezing the fingers, progressively, from the udder end to the tip or by squeezing the teat between thumb and index finger then moving the hand downward from udder towards the end of the teat. And repeat using both hands for speed. Both methods result in the milk that was trapped in the milk duct being squirted out the end into a bucket that is supported between the knees (or rests on the ground) of the milker who usually sits on a low stool to accomplish the milking task.
In early times the cow, or cows, would stand in the field or paddock while being milked. Young stock, heifers, would have to be trained to remain still to be milked. In many countries the cows were tethered to a post and milked. The problem with this method is that it still relies on quiet animals because the milking end of the cow is not restrained. In northern countries where cows are kept in barns in winter, and much of the rest of the year, they are still tethered only by the neck or head, particularly where they are kept in small numbers.
Dairy processing
When it became necessary to milk larger numbers of cows, the cows would be brought to a shed or barn that was set up with bails (stalls) where the cows could be held from moving about while they were milked. One person could milk more cows this way, as many as 20 for a good milker. But having cows standing about in yard and shed waiting to be milked is not good for the cow as she needs as much time in the paddock, grazing, as is possible. It is usual to restrict the twice-daily milking to a maximum of an hour and a half each time. It makes no difference whether one milks 10 or 1000 cows, the milking time should not exceed a total of about three hours each day for any cow.
As herd sizes increased, or as machine-milking became more common and larger herd sizes were possible, there was more need to have efficient milking machines, milking sheds, milk-storage facilities (vats), shed cleaning capabilities and the means of getting cows from paddock to shed and back. Farmers, early, found that cows would abandon their grazing area and walk towards the milking area when the time came for milking. This is not surprising really as, in the flush of the milking season, cows must get very uncomfortable with udders full of milk and the place of relief for them is the milking shed.
As herd numbers increased so did the problems of animal health. In New Zealand two approaches to this problem have been used. The first was improved veterinary medicines that the farmer could use (and the government regulation of the medicines). The second was the generation of veterinary clubs where groups of farmers would employ a veterinarian full-time and share those services throughout the year. It was in the veterinarian's interest to keep the animals healthy and reduce the number of calls from farmers, rather than to ensure that the farmer needed to call for service and pay regularly.
Most dairy farmers milk their cows with absolute regularity at a minimum of twice a day, with some high producing herds milking up to four times a day to lessen the weight of large volumes of milk in the udder of the cow. This daily milking routine goes on for about 300 to 320 days per year that the cow stays in milk. Some small herds are milked once a day for about the last 20 days of the production cycle but this is not usual for large herds. If a cow is left unmilked just once she is likely to reduce milk-production almost immediately and the rest of the season may see her dried off (giving no milk) and still consuming feed for no production. However once a day milking is now being practised more widely in New Zealand for profit and lifestyle reasons. This is effective because the fall in milk yield is at least partially offset by labour and cost savings from milking once per day. This compares to some intensive farm systems in the United States that milk three or more times per day due to higher milk yields per cow and lower marginal labour costs.
Farmers who are contracted to supply whole milk for human consumption often have to manage their herd so that the contracted number of cows are in milk the year round, or the required minimum milk output is maintained. This is done by mating cows outside their natural mating time so that the period when each cow in the herd is giving maximum production is in rotation throughout the year. Northern hemisphere farmers who keep cows in barns almost all the year usually manage their herds to give continuous production of milk so that they get paid all year round. In the southern hemisphere the cooperative dairying systems allow for two months on no productivity because their systems are designed to take advantage of maximum milk production in the spring and because the milk processing plants pay bonuses in the dry season to carry the farmers through the mid-winter. Some year-round milk farms are penalised financially for over-production at any time in the year.
Artificial insemination is common in all high-production herds.
Simple dairying
When few cows were kept, up to about the beginning of the 20th century, the milk was usually consumed by the family keeping the cow(s). When people wanted cream, or butter, they would place the milk in a shallow pan in a cool part of their house—the "dairy"—and allow the butterfat portion of the milk to rise to the surface. After a day or so, usually in the cool of the morning, the surface of the milk was skimmed to remove the cream. The cream could then be churned so that the particles of butterfat would coagulate in the form of butter, leaving buttermilk. Butter is used as a spread on bread, as a cooking fat, as an addition to baked food such as cakes, as a shortening agent for pastries and a thickening in sauces and roux. It can also be purified and used as a heating and lighting oil.
When cheese is to be made the milk it is bought to the right temperature in a vat and then some form of "starter" (rennet, acid or bacteria, see skim milk below) is added to make curds set. The curds are removed and set in moulds or trays (depending on the cheese) and the excess whey is drained. The cheese may be compressed and the exterior may be treated with a variety of preparations, to hasten curing or to form a rind. After the required storage and processing the cheese is sold or consumed by the family.
In some countries this sort of family production is still the norm and the products made from milk vary widely depending on the animal that is milked and the traditional ways of consuming the products made from the milk. For example, today, butter is made in Tibet mainly for candles in monasteries. Desert people still process camel milk in goat-skin bags hung off the side of the camel, using the gait of the beast to process the milk.
Industrial production
Cream and butter
Today, industrially, milk is separated by large machines in bulk. The cream is processed and reduced variously to produce consumer products with varying names depending on the thickness of the cream and its suitability for uses in the kitchen in various countries. Some cream is dried and powdered, some is condensed (by evaporation) and mixed with varying amounts of sugar and canned. Most cream from New Zealand and Australian factories is made into butter. This is done by churning the cream until the fat globules coagulate and form a monolithic mass. The butter mass is washed and, sometimes, salted to improve keeping qualities. The residual buttermilk goes on to further processing. The butter is packaged (25 to 50 kg boxes) and chilled for storage and sale. At a later stage these packages are broken down into home-consumption sized packs. Butter sells for about US$2200 a tonne on the international market.Skim milk
The product left after the cream is removed is called skim, or skimmed milk. Reacting skim milk with rennet or with an acid makes casein curds from the milk solids in skim milk, with whey as a residual. In some countries a portion of cream is returned to the skim milk to make low fat milk for human consumption. By varying the amount of cream returned producers can make a variety of low-fat milks to suit their local market. Other products, such as calcium, vitamin D (in northern hemisphere countries) and flavouring, are also added to appeal to consumers.Casein
Casein is the predominant phosphoprotein found in fresh milk. It has a very wide range of uses from being a filler for human foods, such as in ice cream, to the manufacture of products such as fabric, adhesives, and plastics.Cheese
Cheese is another product made from milk. Whole milk is reacted to form curds that can be compressed, processed and stored to form cheese. In countries where milk is allowed to be processed without pasteurisation a wide range of cheeses can be made using the bacteria naturally in the milk. In most other countries the range of cheeses is smaller and the use of artificial cheese curing is greater. Whey is also the byproduct of this process.Whey
In earlier times whey was considered to be a waste product and it was, mostly, fed to pigs as a convenient means of disposal. Beginning about 1950, and mostly since about 1980, lactose and many other products, mainly food additives, are made from both casein and cheese whey.Yoghurt
Yoghurt (or yoghurt) making is a process similar to cheese making, only the process is arrested before the curd becomes very hard.Milk powders
Milk is also processed by various drying processes into powders. Whole milk and skim-milk powders for human and animal consumption and buttermilk (the residue from butter-making) powder is used for animal food. The main difference between production of powders for human or for animal consumption is in the protection of the process and the product from contamination. Many people in the world today drink milk reconstituted from powdered milk because milk is about 88% water and it is much cheaper to transport the dried product. Dried milk powder is worth about US$2300 a tonne on the international market.Transport of milk
Historically, the milking and the processing took place in the same place: on a dairy farm. Later, cream was separated from the milk by machine, on the farm, and the cream was transported to a factory for buttermaking. The skim milk was fed to pigs. This allowed for the high cost of transport (taking the smallest volume high-value product), primitive trucks and the poor quality of roads. Only farms close to factories could afford to take whole milk, which was essential for cheesemaking in industrial quantities, to them. The development of refrigeration and better road transport, in the late 1950s, has meant that most farmers milk their cows and only temporarily store the milk in large refrigerated bulk tanks, whence it is later transported by truck to central processing facilities.
Milking machines
Milking machines are used to extract milk from cows when the herd is larger than about 4 cows. Milking machines work by using a pulsating vacuum to cause a rubber sleeve round each teat to simulate the effect of hand-milking or of a suckling calf. Vacuum in another pipe transports the flowing milk either to a local container (usually sized to the output of one cow) or, in series with a mechanical pump and heat-exchanger, to a central storage vat or bulk tank, usually refrigerated in most countries.The pulsations of the teat sleeve are controlled by mechanical devices in older machines but modern ones have electronic controls to enhance the milking action.
Milking machines keep the milk enclosed and safe from external contamination. However keeping the milk-transport pipes clean internally is a problem that is more or less solved by adequate washing with chemical solvents and water rinses. Most metalwork in contact with milk should be stainless steel (corrosion-resistant steel) and synthetic rubber is specially designed for milking and milk contact.
Most milking machines are powered by electricity but, in case of electrical failure, there can be an alternative means of motive power, often an internal combustion engine, for the vacuum and milk pumps because milking cows cannot tolerate delays in their scheduled milking without suffering serious milk production reductions.
In the photo above you can see the local container for the milk, a stainless steel can on the far side of the cow, and the two supply pipes to the bottom of the teat cups (one grey, one black). The blue area is the manifold directing vacuum to the cups. Below it is a sight-glass to show the flowing milk so that the milker can see when the milking process is finished and remove the cups. Each teat has a rubber-lined metal cup attached. The cup is connected to pulsing vacuum that you can see goes through a small diameter rubber hose and the small metal tube into the space between the cup and its lining. The pulsations cause the rubber lining to massage the milk from the teat. The milk falls to the bottom of the liner and the other rubber hose conducts the milk down to the sight-glass area. This flow is aided by a constant vacuum, which also holds the cups onto each teat. When the cow is milked this vacuum is shut off and the cups are removed.
Milking shed layouts
Bail-style sheds— This type of milking facility was the first development, after open-paddock milking, for many farmers. The building was a long, narrow, lean-to shed that was open along one long side. The cows were held in a yard at the open side and when they were about to be milked they were positioned in one of the bails (stalls). Usually the cows were restrained in the bail with a breech chain and a rope to restrain the outer back leg. The cow could not move about excessively and the milker could expect not to be kicked or trampled while sitting on a (three-legged) stool and milking into a bucket. When each cow was finished she backed out into the yard again.As herd sizes increased a door was set into the front of each bail so that when the milking was done for any cow the milker could open the door and allow her to exit to the pasture, the next cow walked into the bail and was secured. When milking machines were introduced bails were set in pairs so that a cow was being milked in one paired bail while the other could be prepared for milking. When one was finished the machine's cups are swapped to the other cow. This is the same as for Swingover Milking Parlours as described below except that the cups are loaded on the udder from the side. As herd numbers increased it was easier to double-up the cup-sets and milk both cows simultaneously than to increase the number of bails.
Herringbone Milking Parlours— In herringbone milking sheds, or parlours, cows enter, in single file, and line up almost perpendicular to the central aisle of the milking parlour on both sides of a central pit in which the milker works (you can visualise a fishbone with the ribs representing the cows and the spine being the milker's working area; the cows face outward). After washing the udder and teats the cups of the milking machine are applied to the cows, from the rear of their hind legs, on both sides of the working area. Large herringbone sheds can milk up to 600 cows efficiently with two people.
Swingover Milking Parlours— Swingover parlours are the same as herringbone parlours except they have only one set of milking cups to be shared between the two rows of cows, as one side is being milked the cows on the other side are moved out and replaced with unmilked ones. The advantage of this system is that it is less costly to equip, however it operates at slightly better than half-speed and one would not normally try to milk more than about 100 cows with one person.
Rotary Milking sheds— Rotary milking sheds consist of a turntable with about 12 to 100 individual stalls for cows around the outer edge. The turntable is turned by an electric-motor drive at a rate that one turn is the time for a cow to be milked completely. As an empty stall passes the entrance a cow steps on, facing the centre, and rotates with the turntable. The next cow moves into the next vacant stall and so on. The operator, or milker, cleans the teats, attaches the cups and does any other feeding or whatever husbanding operations that are necessary. Cows are milked as the platform rotates. The milker, or an automatic device, removes the milking machine cups and the cow backs out and leaves at an exit just before the entrance. The rotary system is capable of milking very large herds—up to a thousand cows.
Automatic Milking sheds— Automatic milking or 'robotic milking' sheds can be seen in many European countries. Current automatic milking sheds use the voluntary milking (VM) method. These allow the cows to voluntarily present themselves for milking at any time of the day or night, although repeat visits may be limited by the farmer through computer software. A robot arm is used to clean teats and apply milking equipment, while automated gates direct cow traffic, eliminating the need for the farmer to be present during the process. The entire process is computer controlled.
Supplementary accessories in sheds— Farmers soon realised that a milking shed was a good place to feed cows supplementary foods that overcame local dietary deficiencies or added to the cows wellbeing and production. Each bale might have a box into which such feed is delivered as the cow arrives so that she is eating while being milked.
The holding yard at the entrance of the shed is important as a means of keeping cows moving into the shed. Most yards have a powered gate that ensures that the cows are kept close to the shed.
Water is a vital comodity on a dairy farm, cows drink about 20 gallons (80 litres) a day, sheds need cooling water, drinking water and cleaning water. Pumps and reservoirs are common at milking facilities.
For more applicable information about milking equipments and dairy farming visit: MilkAcademy
Temporary milk storage
Milk coming from the cow is transported to a nearby storage vessel by the airflow leaking around the cups on the cow. From there it is pumped by a mechanical pump and cooled by a heat exchanger. The milk is then stored in a large vat, or bulk tank, which is usually refrigerated until collection for processing.Processing facilities
Topics:- Pasteurization, homogenization
- Cream extraction
- Cheese making
- Buttermaking
- Caseinmaking
- Yogurt processing
Waste disposal
In countries where cows are grazed outside year-round there is little waste disposal to deal with. The most concentrated waste is at the milking shed where the animal waste is liquefied (during the water-washing process) and allowed to flow by gravity, or pumped, into composting ponds with anaerobic bacteria to consume the solids. The processed water and nutrients are then pumped back onto the pasture as irrigation and fertilizer.
Surplus animals are slaughtered for processed meat and other rendered products.
In the associated milk processing factories most of the waste is washing water that is treated, usually by composting, and returned to waterways. This is much different from half a century ago when the main products were butter, cheese and casein, and the rest of the milk had to be disposed of as waste (sometimes as animal feed).
In areas where cows are housed all year round the waste problem is difficult because of the amount of feed that is bought in and the amount of bedding material that also has to be removed and composted. The size of the problem can be understood by standing downwind of the barns where such dairying goes on.
In many cases modern farms have very large quantities of milk to be transported to a factory for processing. If anything goes wrong with the milking, transport or processing facilities it can be a major disaster trying to dispose of enormous quantities of milk. If a road tanker overturns on a road the rescue crew is looking at accommodating the spill of 10 to 20 thousand gallons of milk (45 to 90 thousand litres) without allowing any into the waterways. A derailed rail tanker-train may involve 10 times that amount. Without refrigeration, milk is a fragile commodity and it is very damaging to the environment in its raw state. A widespread electrical power blackout is another disaster for the dairy industry because both milking and processing facilities are affected.
In dairy-intensive areas the simplest way of disposing of large quantities of milk has been to dig a big hole and allow the clay to filter the milk solids as it soaks away. This is not very satisfactory, but neither the farmer nor the processor wants to lose that much income anyway! In most cases it is an original failure of the infrastructure (electrical distribution or transport system) that caused the initial disaster.
Diseases associated with the dairy industry
- Leptospirosis is one of the most common debilitating diseases of milkers, made somewhat worse since the introduction of herringbone sheds because of unavoidable direct contact with bovine urine
- Cowpox is one of the helpful diseases; it is barely harmful to humans and tends to inoculate them against other poxes such as chickenpox
- Tuberculosis (TB) is able to be transmitted from cattle, mainly via milk products that are unpasteurised and many dairy-producing families consume milk that way. In the important dairy exporting countries TB has been eradicated from herds by testing for the disease and culling suspected animals
- Brucellosis is a bacterial disease transmitted to humans by dairy products and direct animal contact. In the important dairy exporting countries Brucellosis has been eradicated from herds by testing for the disease and culling suspected animals
- Listeria is a bacterial disease associated with unpasteurised milk and can affect some cheeses made in traditional ways. Careful observance of the traditional cheesemaking methods achieves reasonable protection for the consumer
Ethical objections to the use of dairy products
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Notes
External links
- Milking in the early days
- National Dairy Research Institute
- Read Congressional Research Service (CRS) Reports regarding the Dairy Industry
- The story of barbed wire is intimately bound up in dairying
- University of Guelph Dairy Science and Technology Education Series -- Online technical information about dairy products.
- Nutrition Facts about Dairy and Egg Products - Titiland Nutrition Database.
- Dairy Science and Food Technology: Starters, Probiotics, Cheese and Antimicrobial Systems
- PETA page on the Health Risks of Dairy
- Health Benefits of Dairy
- Dairy research and information from New Zealand
- Dairy water heating technologies in NZ
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