162 



THK PKESERVATION OF MILK 



recognised as unreliable. At present there is only one siui/Ji' way of arriving at 

 the object in view, and that is by thickening the milk and adding sugar. 



This so-called "condensed milk" as manufactured in particular by the 

 " Anglo-Swiss Condensed Milk Company " in their chief factory at Cham, on 



Lake Zug, and in a number of branch 

 establishments outside Switzerland is 

 prepared in the following manner : The 

 fresh new milk is purified by centrifugal 

 force, and is then heated on a water- 

 bath until nearly boiling, and mixed (in 

 a wooden vat fitted with a steam coil) 

 with 1 2 per cent, of cane-sugar. When 

 this is dissolved the liquid is pas>rd 

 through a fine sieve and transferred to 

 a vacuum pan, where the thickening 

 process is effected at a temperature of 

 5o-6o C. As soon as the requisite de- 

 gree of consistency is attained the milk 

 is run off, rapidly cooled, and packed in 

 clean tins, which are soldered air-tight. 

 Commercial condensed milk contains 

 about 25 per cent, of water and 50 per 

 cent, of sugar, the remainder consisting 

 of albumen (12 per cent.), fat (n per 

 cent.), and ash (2 per cent.). 



Some of the germs present in the new 

 milk, especially the lactic acid bacteria, 

 are already killed by the aforesaid heat- 

 ing before and during the thickening process. A few, however, survive this, 

 and are found to be still alive in the finished product, but not in a condition 

 to do any damage, since the high concentration plasmolyses the germs, retarding 

 their development and so preventing decomposition. By reason of its high con- 

 tent of sugar, however, this condensed milk is unsuitable for the nourishment of 

 infants. 



FIG. 51. 



Illustration of the effect of Pasteurising milk. 



The black square represents the germ-content of 

 raw milk per unit of space, that of the same 

 sample after Pasteurisation being shown by 

 the small white square. (4/'tcr Jlusscll.) 



