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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. For New Zealand a dairy is a shop selling convenience-food products.
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 bales 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 a milking 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, milk-storage facilities, shed cleaning capabilities and the means of getting cows from paddock to shed. Farmers 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.
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 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 once she is likely to reduce milk-production almost immediately and the rest of the season may see her dried off and still consuming feed for no production.
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. 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.
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 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 was then churned so that the particles of butterfat would coagulate in the form of butter. 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.
The product left after cream is removed is called skim , skimmed , or low fat milk. Reacting skim milk with rennit or with an acid makes casein curds from the milk solids in skim milk, with whey as a residual.
Cheese is another product made from milk. Whole milk is reacted to form curds that can be compressed, processed and stored to form cheese. Whey is also the byproduct of this process.
Lactose and other products, mainly food additives, are made from both types of whey. Yoghurt 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 powers for human and animal consumption and buttermilk (the residue from butter making) powder is used for animal food. Many people in the world today drink milk reconstituted from powdered milk becaue milk is about 88% water and it is much cheaper to transport the dried product.
Historically, the milking and the processing took place in the same place: on a dairy farm. The development of refrigeration and road transport has meant that most farmers only milk their cows and temporarily store the milk in large refrigerated tanks, whence it is later transported by truck to central processing facilities.
In countries where small numbers of cows are kept the number of products made from milk are limited - often to as few as two. 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 products from milk and are able to choose what to make depending on the price of any product combination at any time.
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