Dairy

A dairy is a facility for the extraction and processing of animal milk (mostly from cows, sometimes from buffaloes, sheep 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. Over the years, Dairy has become a multibillion-dollar industry.

Milking sheds

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.

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Milking machines

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.

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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.

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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.

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Milking shed layouts

Bail-style sheds—

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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.

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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.

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Herringbone Milking Parlours—

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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.

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Swingover Milking Parlours—

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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.

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Rotary Milking sheds—

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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.

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Robotic Milking sheds—

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Robotic milking sheds can be seen in many European countries and also in research facilities in Australia and New Zealand. 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. Computers direct the automatic removal of the milking cups as the flow reduces.

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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.

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Processing facilities

Topics:

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• Pasteurization, homogenization
• Cream extraction
• Cheese making
• Buttermaking
• Caseinmaking
• Yogurt processing