Arriving in the city in iced cars the milk is taken to one of the elaborate plants in which it is pasteurized and bottled, if that has not been done at the country station. The machinery used in these plants is getting more and more perfect and expensive and leaves little to be desired as to sanitary requirements and economy in handling. Pasteurizers, bottling machines, bottle-washing machines, conveyors, etc., are wonders of ingenuity, and one needs only to see one of these modern plants to understand that in a large city milk can only be handled to advantage in expensive establishments.
Skim Milk is one of the cheapest of foods and under proper regulations its sale should not be prohibited. The reason why in times past skim milk has been discredited and excluded from sale was that, as produced by the old methods of raising the cream, before the advent of the separator, it was always more or less old and sour before it was available and certainly before it could be distributed to consumers. Under such conditions it was hardly ever fit for human food. But when produced by the separator and pasteurized and cooled immediately after—within a few hours after milking, which is entirely feasible—it is an excellent and nutritious food for adults and even for children over two years of age. Ripened with a pure culture of lactic acid bacteria, it makes a healthful, refreshing drink, like buttermilk. Only when it is allowed to sour without proper care or control does skim milk, as whole milk does, become unfit for food or drink. On a cold winter morning when men are going to work (or perhaps are looking for work which they cannot find), and children are on their way to school, often underfed, a street-corner wagon or stand where boiling hot, fresh, sweet skim milk might be distributed at a cent or two a glass would be a blessing in any city.
Pasteurizing and bottling milk in a Borden plant
CREAM
When new milk is left at rest the cream will rise to the top and after 12 to 24 hours a cream-line can be seen in the bottle. This cream-line is sharper and more easily seen in raw milk than in pasteurized milk and its absence is not always a sure sign of lack of richness or purity of the milk. By cooling the milk thoroughly so that it will keep, almost all the cream will be at the top in forty-eight hours and can be skimmed off. The cream can be used for coffee or on cereals or fruits or puddings; the skim milk left will still hold ½% or more of butter-fat and can be used to drink or for cooking.
The Separator.—On the farm or in the creamery the cream is no longer raised by gravity, that is, by letting the milk “set” either in shallow pans on the kitchen shelf or in deep cans in ice water, but the fresh, warm milk is run through the separator in a continuous stream.
Early conception of the separator
It was noticed that the rising of the cream due to the difference in specific gravity between the butter-fat and the milk-“serum” (the watery solution of the other constituents) might be greatly hastened by subjecting the milk to centrifugal force. This physical phenomenon was taken advantage of in the first conception of the separator where it was shown that if a pail of milk was whirled around like a stone in a sling the heavier milk-serum would be thrown towards the bottom of the separator pail with so much greater force than the lighter cream (butter-fat mixed with a small part of the serum) that the separation which would take 48 hours in the milk at rest, could be accomplished in a few minutes when exposed to centrifugal force. From this early crude attempt the continuous bowl-separator was developed and still later a number of divisions in the bowl were designed which increased the capacity and efficiency of the machine wonderfully. The most successful separator was designed by Dr. Gustaf De Laval of Sweden and the machines bearing his name are used all over the world where butter is made. But there are many other excellent separators on the market.