MILK PRODUCTS 



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resistance is also increased when the temperature is lowered ; 

 and conversely it is diminished when the temperature is raised. 

 The rise of the cream cannot, however, be accelerated in this 

 way because the higher temperatures are favourable to the 

 development of lactic acid, which, by its action on the casein, 

 greatly increases the resistance. 



Any disturbance of the milk, either by agitation or by 

 convection currents due to changes of temperature, tends to 

 redistribute the fat globules through the liquid, and so hinders 

 the formation of cream. The milk should, therefore, be 

 cooled to the temperature of the surroundings either before 

 or immediately after it is set for cream. In the method of 



FIG. 27. 



shallow setting, the cooling takes place naturally at a rapid 

 rate owing to the large surface exposed. 



The success of the various methods of deep setting depends 

 on the principles described above. The cans used in this 

 process are made of metal, with rounded corners, usually about 

 20 inches deep and 10 x 10 inches square. They are, there- 

 fore, capable of holding between 50 and 60 pints of milk. 

 When filled, they are immersed in a large vat through 

 which a current of water passes, as shown in the diagram 

 (Fig. 27). In the original Swartz process, the vats were 

 packed with ice. The milk is rapidly cooled down ; but as 

 the cooling takes place from the sides and bottom of the vessel, 

 no vertical currents are set up, and there is no interference 

 with the rise of the fat globules from this cause. The surface 

 exposed to the air is so much smaller, compared with that in 

 the method of shallow setting, that the milk does not become 



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