THE OLD METHOD OF CREAM-SEPARATION. Ill 



takes place so slowly that it is no longer worth while to let the 

 milk stand. 



The sooner the vertical currents, due to the cooling of the milk, 

 cease, and the fatty globules are enabled to exercise their tendency 

 to rise to the surface without hindrance, the more successfully will 

 the process of cream-raising be carried on. If metal vessels are 

 used in cream-raising, and care is taken that the milk is cooled by 

 the application of cold to the sides and bottom of the vessel, vertical 

 currents may be altogether avoided, and creaming may be permitted 

 to take place under the most favourable possible circumstances. 



There are no substances which, when added to milk, hasten the 

 process of creaming, and if chemicals are added to milk for the 

 purpose of retarding premature coagulation, such treatment is liable 

 to be regarded in the light of adulteration. 



In the case of comparatively high equable temperatures from 

 10 C. upwards the collection of cream takes place by the formation 

 of a comparatively small layer of cream at first, which is gradually 

 increased. The fatty globules collect in the cream-layer according 

 to their size, the largest globules coming to the surface first, and the 

 smaller ones less quickly. In the case of lower equable tempera- 

 tures 10 C. and downwards the milk-serum is comparatively 

 viscous, and in consequence the fatty globules experience in their 

 movement greater internal friction. As long as the fatty globules 

 in cream-raising are not brought into close contact with one another, 

 they find their way to the surface undisturbed, more or less quickly, 

 without reference to their size. In a short time, however, it is 

 impossible for the larger globules to overtake unhindered the smaller 

 ones. Blocks occur in the ever-increasing swarm of upward-striving 

 globules, and there is seen, as a rule, after a longer time, a com- 

 paratively thick layer of cream, which, owing to the fact that the 

 fatty globules are slowly pressing up on one another, gradually 

 becomes more concentrated. 



The lower the temperature at the end of the creaming period, 

 the greater is the expansion, weight, and amount of water in the 

 cream-layer, and the smaller is the percentage of its fat, after the 

 lapse of a certain time and in the case of a fixed degree of tempera- 

 ture. On the other hand, if milk of similar composition and under 

 similar conditions be set for creaming, the higher the creaming 

 temperature the less will be the cream, and that cream will contain 

 less water and correspondingly more fat, besides being more viscous. 



