176 Condensed Milk and Milk Powder 



that, during the process of freezing, there is a partial separation of 

 the watery portion from the caseous material. The casein contracts 

 and the watery portion freezes. When melted, the emulsion is less 

 complete than it was before freezing. The casein remains in its con- 

 tracted form and robs the product of its original smoothness. 



Blown Evaporated Milk Due to Chemical Action. — While prop- 

 erly processed evaporated milk is perfectly sterile, and from the 

 biological point of view, keeps indefinitely, the cans of very old, 

 evaporated milk may bulge, as the result of the action of the acid 

 in the milk on the container. Evaporated milk contains from .35 

 to .50 per cent, acid (calculated. as lactic acid). When the tin cans 

 are filled with the evaporated milk, the tinplate is bright and untarn- 

 ished, both, inside and out. After the sterilizing process, the inside 

 surface of the cans is dark and dull. This is caused by the com- 

 bined action of acid and heat, which seems to we'aken the tinplate. 

 This phenomenon is further illustrated by the fact that where cream- 

 eries pasteurize their skimmilk and return it to the patrons in the 

 milk cans hot, the milk cans are short-lived ; they soon corrode and 

 begin to leak. ' 



The acid in the evaporated milk continues to act on the tin- 

 plate of the can after manufacture and in the case of very old 

 evaporated milk, the acid may decompose a considerable part of the 

 iron. This action is accompanied by the evolution of hydrogen gas, 

 which causes the cans to bulge. This action is hastened by con- 

 tinued exposure of the goods to high temperatures (summer heat). 

 This fact was experimentally demonstrated, 1 also, by scratching 

 the bottom of tin cans on the inside with a file, then filling the cans 

 with a .4 per cent, solution of lactic acid and acetic acid, respec- 

 tively. After sealing, the cans were sterilised in the autoclave, so 

 as to avoid any possibility of bacterial action. After cooling, these 

 sterilized cans were incubated for some time at 96 degrees F. The 

 cans containing the dilute acid began to swell, while the check cans, 

 containing distilled water only, remained normal. 



Brown Evaporated Milk 



General Description.— It is the aim of the processor to so 

 govern the sterilizing process as to give the evaporated milk a rich, 



1 Hunziker and Wright, Indiana Agricultural Experiment Station. Results not published 



