DAIRY MACHINERY AND EQUIPMENT. The de velopment of modern dairy machinery has been influenced by sev eral factors, a few of which are: (I) expansion in the use of dairy products and dairy by-products; (2) the urge to save labour; (3 ) development of large volume production and distribution agencies; (4) greater use of pasteurization; (5) use of stainless steel; (6) the development of larger dairy farm units; (7) greater use of the milking machine on the farm ; (8) changes in transportation resulting from better roads and the use of trucks.
The above factors have influenced the extent and use of dairy machinery in all countries of the world where dairying is a major enterprise. The greatest changes, however, have taken place in the United States where the industry is relatively new.
The shortage and the high price of desir able labour for milking cows has extended the use of milking machines. It is difficult to estimate the proportion of cows milked by machine but estimates from men selling milking machines in the United States vary from Io to 15%.
The milking machine has been developed to imitate the suction of the calf on the cow's teat. There have been many refinements in the machines that have not only made them more efficient, but more easily cleaned and more durable. When properly operated a milking machine will milk as efficiently as the average hand milker. The cows are usually stripped by hand after the machine is removed.
The usual type of milking machine has a central suction pump and the vacuum line is piped throughout the barn where the cows are housed. The milker unit may be attached any place in the suction line. The milking unit consists of a metal bucket with the pulsator on the cover. A rubber tube runs from the pulsator to the suction line. Another tube runs from the pulsator to the cow's udder where it ends in four teat cups. The suction is applied, then released. The rapidity of the pulsation is con trolled by the operator. With the development of small gasoline engines, portable suction pumps have been developed which are pushed through the barn and become a part of the milker unit. This type of milker reduces the cost of installation by eliminat ing the suction line.
The success of the milking machine on a dairy farm depends to a great extent on the ability of the operator to adjust the ma chine to the individual cow so that she will give her maximum production and at the same time save enough time and labour with the machine to justify the expense of the machine.
When milk comes from the cow it is about 1 oo° F. It is important that this milk be cooled immediately to a point below that at which bacteria grow rapidly. It is desirable to cool to 5o° F. as soon as possible. On the dairy farm this is usually accomplished by allowing the milk to run in a thin film over a cooled metal surface where it is cooled and aerated. Most coolers consist of a series of tubes through which cold water is passing. In some cases the milk may first contact water-cooled tubes and in the lower half tubes cooled with brine. The thin film of milk may also cause undesirable odours to pass out of the milk. When the milk is held on the farm before delivery, it is placed in 8 or io-gallon cans and put into a tank of water with some provision for holding the temperature at a desirable level. When the milk is separated at the farm it is best to separate it soon after milking and without cooling.
Milk is skimmed more efficiently by a centrifugal separator at about 9o° F., and the skim milk at this temperature is about right for feeding calves.
The centrifugal separator has re placed the gravity systems of separation of cream from the rest of the milk. The separation of milk by centrifugal force is based on the fact that the butterfat in milk is in the form of small globules which are lighter than the rest of the milk. The specific gravity of milk is 1.032 and of butterfat is .93 at 6o° F. (15.5° C.) . In the early development of the separator the cost of separators was high, and as a result whole milk was hauled to skimming stations or to creameries where it was skimmed and each farmer was given a proportionate amount of skimmed milk. In 1890 the hand separator was put on the market. This changed the type of creameries from whole milk to gathered cream cream eries, reduced the hauling of milk and made skimmed milk more easily available. In all parts of the world the separator is an es sential item of equipment where cream is sold. Even on the farms where whole milk is sold it is necessary to separate some milk for raising calves.
The essential feature of the centrifugal cream separator is a rapidly revolving bowl which contains a series of discs. The bowl is mounted on a spindle under a supply can holding the milk. Openings at different locations at the top of the bowl permit the milk to enter, and the cream to come out one outlet and the skimmed milk another in a continuous flow. The bowl of a hand separator revolves between 6,000-8,00o r.p.m. The discs divide the milk into thin layers, and the centrifugal force developed in the rapidly revolving bowl causes the heavier part of the milk to be forced to the outside of the bowl and out of the skim milk outlet. The butterfat, being lighter than the rest of the milk, comes to the centre and is moved out of the cream outlet. The richness of the cream may be regulated by the position of the cream outlet. As previously stated, cream testing 30-35% butter fat is desirable. When properly handled, the skimmed milk should not contain more than •1% butterfat.
It is common knowledge to users of the centrifugal separator that the inside of the bowl frequently gath ers foreign particles from the milk. This fact formed the basis for the construction of the centrifugal clarifier, for removing foreign material from market milk. The clarifier resembles the separator with the exception that the bowl is constructed so there will be no separation in the milk and there is more room between the discs and the inside of the bowl. The milk flows through the rapidly revolving bowl and out a single outlet.
are used in milk plants or creameries where large volumes of milk and cream are pasteurized for market milk or for some operation in processing milk or cream. The type of pas teurizer and cooling equipment will depend upon whether the holding method (143° for 3o min.) or the flash method (160° for 15 sec.) of pasteurization is used. A commonly used pas teurizer is a rectangular insulated vat made of stainless steel with a tight cover of the same material. Some device for slow agitation is mounted in the vat. The vat is equipped so that hot water may be applied to heat the milk to the proper temperature. After this, water or brine may be turned into the vat for cooling, or the warm milk may be pumped over a tubular cooler. A recording ther mometer may record the temperature cycle. In the case of high temperature pasteurization, special machinery is necessary to apply heat at a higher temperature for a short period.
The bottling of milk may be the final plant operation in a system of pasteurization of milk where the warm milk flows over a tubular cooler into an automatic bottle filler and capper. The inspected bottles are fed onto a revolving table where the bottles are filled and capped at the end of the revolu tion. The capping of bottles by hand is a source of contamination prohibited on most markets. In addition to the usual paraffined cap some grades of milk require a paper or metal cover to protect the top of the bottle. In this event this is made another operation of the machine. Hand operated filling and capping ma chines are available for small dairies. In 1939 a few markets were using single service paper bottles.
Shortly after the adoption of the hand separator the butter factory in the United States changed from receiving whole milk to handling cream for churning. Cream eries were built to handle cream from farmers who delivered their own cream in an area having i,000 or more cows. Now automo biles and all-weather roads have extended the area available to any one creamery. In the State of Minnesota in 1938 there were 856 creameries. Of this number 628 were co-operative creameries.
For each I oolb. of 3 5 % cream delivered to a creamery there are approximately 571b. of buttermilk that has little value com mercially. In the smaller creameries this is generally sold to farmers for hog feeding. In the larger creameries the disposal of the buttermilk is a problem. This has been overcome by drying the buttermilk to make dried buttermilk, or by removing most of the water to produce semi-solid buttermilk which is stored in wooden barrels. Most of the buttermilk is fed to hogs, calves, and chickens. The cost of drying equipment is high, and only the larger creameries can justify the expenditure. In some com munities 2 5-3o creameries may truck buttermilk to a central drying plant.
The churning of cream into butter depends on the fact that the butterfat in cream is in the form of small globules. At the proper temperature (around 5o° F.) and with sufficient agitation, the but ter will gather together in the form of granules and separate from the buttermilk. When the butter particles reach the size of a ker nel of corn, the buttermilk can be drawn off without an appre ciable loss of butterfat. The butter is then washed with water of about the same temperature as the buttermilk. After the wash water is removed, salt may be added if desired and the butter worked. During working, the butter is kneaded into a compact mass, the salt incorporated and the moisture content standardized. In the United States, butter must contain 8o% of butterfat by weight.
In a creamery the cream is churned in a barrel-like combined churn and worker that will handle approximately I,000lb. of finished butter. The churn is commonly made of wood and is mounted so that it will revolve. The butter is washed, salted, and worked in the churn, and is ready for packing into tubs or for printing when taken from the churn. The upright dasher churns so common on farms in the past have been eliminated in favour of some kind of revolving barrel churn. The making of butter on the farm is gradually being eliminated due to the ease of trading but ter fat for butter at the dairy plant and for the reason that farm made butter is generally inferior in quality to creamery butter.
In the making of cheddar cheese, whole milk is coagulated with rennet. The liquid portion or whey is removed and the curd is heated and allowed to drain. The curd is then cut, salted and packed in cloth lined hoops, and placed in a press for about 24 hours to mould the cheese into the desired shape. The cheese is then moved to a curing room where a desirable temperature for curing may be maintained. This may vary from 40° F. to 6o° F. The length of time and temperature determine the ripeness of the cheese. Usually 6-8 months are required to insure satisfactory ripening. The equipment for cheeseraking is more simple than that required for other dairy products. Rec tangular vats for holding the milk, presses, and a curing room are the most essential items. The development of process cheese has stimulated the cheese industry in the United States. In making process cheese the rind is removed and the cheese is ground, heated, and packaged when hot. Cheese of various ages and types are blended to secure the desired flavour and body. In this way the flavour, body and texture, colour, and other properties may be standardized.
Ice cream has changed from a luxury to a delicious food product universally used. Centralized methods of manufacture and distribution have extended the use of ice cream at a price within the reach of all. The tub freezer requiring ice has been replaced by the continuous freezer made of stainless steel and using brine or ammonia as a refrigerant. The ice cream mix is partially frozen and whipped in the freezer and then placed in a low temperature room (below — io° F.) to harden. The very general adoption of electrical refrigerators in the home has made it possible to carry a supply of ice cream in the home. Refriger ated trucks and the use of dry ice have facilitated the distribution of ice cream.
and Raffetto, Ice Cream (1924) ; O. F. Bibliography.-Turnbo ;w and Raffetto, Ice Cream (1924) ; O. F. Hunziker, Condensed Milk and Milk Powder (4th ed. 1926), and The Butter Industry (end ed. 1927) ; J. L. Sammis, Cheese Making (193o) ; M. Mortensen, Management of Dairy Plants (1938) ; H. H. Sommer, Market Milk and Related Products (1938) ; U. S. Public Health Serv ice, Milk Ordinance and Code (1939). U. B. FH.)
