BUTTER-MAKING. The process of making butter from cow's milk is divided into the opera tions of creaming, churning, and working or finishing. The fat in milk exists in the form of minute globules in suspension. In the opera tion of creaming. the separation of these globules from the rest of the milk is effected either by setting the milk in shallow pans or in deep calls in cold water, or by means of a cream-separator. 1 t is possible to make butter by churning the whole milk without first creaming it, and this was undoubtedly the practice in earlier days, but there is far greater loss of fat in this way, and the churning of large quantities of milk is very laborious. In both shallow and deep setting the cream is raised by gravity. The fat-globules, being lighter than the water and other con stituents of the milk, gradually rise to the sur face on standing, carrying with them some of the other constituents also. The time required and the completeness of the operation depend upon the size of the fat-gobules, which differs in the ease of different breeds of cows, the larger globules rising more readily. The fat left in the skim milk consists mostly of small globules which failed to rise as soon as the others. The fat content of the skim milk is the measure of the efficiency of creaming. In shallow setting in pans the force of gravity alone is relied upon, the milk being set as quickly as possible after it is drawn, and the cream skimmed off after standing twenty-four hours or longer. The loss of fat by this method is quite large, amounting to about 20 per cent.. and the skim milk contains from 0.5 to 1.5 per cent. of fat. In deep setting, cans abdut 18 inches deep are used, and these are immersed or partially submerged in cold water, preferably at about 10° F. The low tempera ture causes the globules to rise more rapidly and more completely than in shallow setting. The milk is allowed to stand in these cans for eigh teen to twenty-four hours, and the cream is then removed from the top by 111P:111S of a dipper, or the skim milk is drawn off from below, leaving the layer of cream in the can. The latter method is the least wasteful, and by it the fat in the skim milk may be reduced to as low as 0.2 per cent. under favorable conditions. Efficiency in deep setting depends upon cooling the milk rapidly as soon as it is drawn, and in maintain ing; a temperature a little above freezing. If
the temperature is allowed to rise there is a material loss of fat. in the skint milk. Tho separator has quite generally superseded deep or shallow setting in creameries and in large dairies during the past few years. In this method the cream is separated from the milk by centrifugal force, in a bowl or drum, revolving at a high rate of speed, from 5000 to S000 revolutions a minute and even more. The milk enters through a tube reaching to the centre and near the bot tom of the howl. where the high rate of speed causes the heavier milk fluid (the serum) to gravitate toward the circumferen•e of the bowl, while the lighter cream remains near the centre and rises to the upper part of the howl. The skim milk flows out through a side tube, and the cream a second tube leading from the centre near the top. The operation is continuous, milk flowing into the bowl and skim milk and cream flowing out of it without interruption. The rate of separation varies with the size and capacity of the machine, the smaller hand sepa rators skimming from 200 to 500 pounds an hour, and the larger forms 2000 pounds and over. lty means of various appliances within the howl the separation of the fat is made quite complete, the skim milk from a good separator properly operated containing only about 0.1 per cent. of fat and in some cases only 0.05 per cent.
The cream obtained by setting or by the separator may be (dimmed at once, as is the case in making sweet-cream butter. or may be first 'ripened' or soured. The object in ripening is to develop the characteristic flavors of butter and a slight acidity which aids in elmrning and affects the texture of the butter. Ripening is effected by adding to the cream a 'starter' of sour skim milk, buttermilk, or cream from a preceding churning, or a commercial preparation of the desired micro-o•ganisms called a laetie ferment or pure culture. It is necessary to prevent ac cess to the cream of any germs which may cause improper souring. or impart an taste or quality to the butter, and it is with this view that pure cultures are used for ripening. Pasteurization of the milk or cream used in butter-making, which is practiced quite exten sively in some countries. has the same object, the theory being to kill all the germs which may be in the milk or cream, and add only such as are desirable.