Page:EB1911 - Volume 07.djvu/774

Rh butter-worker unnecessary, whilst the butter produced has a better grain. Scotch hands (fig. 17), made of boxwood, are used for the lifting, moulding and pressing of butter.

In the centrifugal cream-separator the new milk is allowed to flow into a bowl, which is caused to rotate on its own axis several thousand times per minute. The heavier portion which makes up the watery part of the milk flies to the outer circumference of the bowl, whilst the lighter particles of butter-fat are forced to travel in an inner zone. By a simple mechanical arrangement the separated milk is forced out at one tube and the cream at another, and they are collected in distinct vessels. Separators are made of all sizes, from small machines dealing with 10 or 20 up to 100 gallons an hour, and worked by hand (fig. 18), to large machines separating 150 to 440 gallons an hour, and worked by horse, steam or other power (fig. 19). Separation is found to be most effective at temperatures ranging in different machines from 80° to 98° F., though as high a temperature as 150° is sometimes employed. The most efficient separators remove nearly the whole of the butter-fat, the quantity of fat left in the separated milk falling in some cases to as low as 0.1. When cream is raised by the deep-setting method, from 0.2 to 0.4% of fat is left in the skim-milk; by the shallow-setting method from 0.3 to 0.5% of the fat is left behind. As a rule, therefore, “separated” milk is much poorer in fat than ordinary “skim” milk left by the cream-raising method in deep or shallow vessels.

The first continuous working separator was the invention of Dr de Laval. The more recent invention by Baron von Bechtolsheim of what are known as the Alfa discs, which are placed along the centre of the bowl of the separator, has much increased the separating capacity of the machines without adding to the power required. This has been of great assistance to dairy farmers by lessening the cost of the manufacture of butter, and thus enabling a large additional number of factories to be established in different parts of the world, particularly in Ireland, where these disc machines are very extensively used.

The pasteurizer—so named after the French chemist Pasteur—affords a means whereby at the outset the milk is maintained at a temperature of 170° to 180° F. for a period of eight or ten minutes. The object of this is to destroy the tubercle bacillus, if it should happen to exist in the milk, whilst incidentally the bacilli associated with several other diseases communicable through the medium of milk would also be killed if they were present. Discordant results have been recorded by experimenters who have attempted to kill tubercle bacilli in milk by heating the latter in open vessels, thereby permitting the formation of a scum or “scalded layer” capable of protecting the tubercle bacilli, and enabling them to resist a higher temperature than otherwise would be fatal to them. At a temperature not much above 150° F. milk begins to acquire the cooked flavour which is objectionable to many palates, whilst its “body” is so modified as to lessen its suitability for creaming purposes. Three factors really enter into effective pasteurization of milk, namely (1) the temperature to which the milk is raised, (2) the length of time it is kept at that temperature, (3) the maintenance of a condition of mechanical agitation to prevent the formation of “scalded layer.” Within limits, what a higher temperature will accomplish if maintained for a very short time may be effected by a lower temperature continued over a longer period. The investigation of the problem forms the subject of a paper in the 17th Annual Report of the Wisconsin Agricultural Experiment Station, 1900. The following are the results of the experiments:—

1. An exposure of tuberculous milk in a tightly closed commercial pasteurizer for a period of ten minutes destroyed in every case the tubercle bacillus, as determined by the inoculation of such heated milk into susceptible animals like guinea-pigs.