In many northern-hemisphere countries a dairy is a facility for the extraction and processing of animal milk (mostly from cows, sometimes from buffaloes or goats) for human consumption. The end product of such processes are known as dairy products. In Australia a dairy is also a shop or company that sells dairy products. In New Zealand a dairy is a shop selling convenience-food products. A dairy farm produces milk and a dairy factory processes it.
Historically, the milking and the processing took place in the same place: on a dairy farm. 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.
When it became necessary to milk larger numbers of cows—especially in such as New Zealand and Australia where the cows are out in the open all year round—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.
One of the concerns for dairy farmers is the need to milk cows with absolute regularity twice a day. This twice-a-day milking 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.
Farmers who are contracted to supply whole milk for human consumption (in New Zealand called "town-milk supply") 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.
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 shortning agent for pastries and a thickening in sauces and rues. 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 temparature 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 usually 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 monastries. Desert people still process camel milk in goat-skin bags hung off the side of the camel and using the gait of the beast to process the milk.
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.
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 and flavouring, are also added to appeal to consumers.
Casein is the predominant phosphoprotein found in fresh milk. It has a very wide wide range of uses from being a filler for human foods, such as in ice cream, to the manufacture of products such as fabric, glues and plastics.
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.
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 (or yogurt) making is a process similar to cheese making, only the process is arrested before the curd becomes very hard.
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 hight cost of transport, primitive trucks and poor quality of roads. Only farms close to factories could afford to take whole milk to them, which was essential for cheesemaking in industrial quantities. The development of refrigeration and road transport, in the late 1950s, has meant that most farmers milk their cows and only temporarily store the milk in large refrigerated tanks, whence it is later transported by truck to central processing facilities.
Considerations of size
In countries where small numbers of cows are kept the number of products made from milk are limited—often to as few as two— and disposal of unusable residuals is a problem. But where large herds are common, say more than 50 cows, the economics of making as many products as possible at a central factory is important. Modern milk-processing factories can make as many as 30 different products from milk, leaving no waste and are able to choose what to make depending on the price of any product combination at any time.
Milking sheds are the buildings in which milk is exacted from cows and stored until collected for processing. Shed layouts are important to the milking process, to the cow as much as the farmer. For example when steel pipe rails were first introduced as bail rails (replacing less sanitary wooden rails) the farmers noticed a rapid drop in milk production. This was later found to be because of residual electrical currents in the rails caused from leakages from electric motors operating the milking plant. The cows were more sensitive than the farmers.
Milking machines are used to extract milk from cows for human consumption. Modern milking machines work using a pulsating vacuum to cause a rubber sleeve round each teat to simulate the effect of hand milking or a suckling calf. The same vacuum transports the flowing milk to a local container, usually sized to the output of one cow, or in series with a mechanical pump to a central storage vat, usually refrigerated in most warmer 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 many instances there will be an alternative means of motive power, often internal combustion engines, for the air and milk pumps because milking cows cannot tolerate delays in their scheduled milking without suffering milk production reductions.
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 it 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 it 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 18 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.
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 tank, which is usually refrigerated until collection for processing.
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 them 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.
New Zealand terminology
In New Zealand, a dairy, or "corner dairy", is a suburban or rural shop stocking groceries. The local dairy is often a popular destination for children after school, where they can get a cheap ice cream, milk shake or a mixture of lollies.
Dairys are usually family businesses.
In New Zealand English a farm is a dairy farm, milking facilities are milking sheds or cow sheds, and processing facilities are dairy factories.
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 innoculate 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
Many people concerned about animal welfare (especially vegans) do not consume dairy products. An increasing number of dairy cows are being raised on factory farms, which some people consider cruel. On many farms, the calves are separated from their mothers within days of birth to prevent the calf from drinking the milk so that humans can drink it instead. Some of the calves born by dairy cows are raised in crates for veal and are slaughtered three to eighteen weeks later. On many farms, once a dairy cow's milk production decreases, she is also slaughtered at an age that is a fraction of her natural lifespan. For these reasons, either in an attempt to reduce animal suffering or to prevent animals from being killed, some people choose to not consume dairy. Some also object to eating dairy for environmental reasons.