268 UNSWESTDNSD CONDENSED MILK 



casein remains in its contracted form and robs the product of its 

 original smoothness. 



Blown Evaporated Milk Due to Chemical Action. While 

 properly 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 Avith the evaporated milk, the tinplate is 

 bright and untarnished, both, inside and out.. After the sterilizing 

 process, the inside surface of the cans is dark and dull. This is 

 caused by the combined action of acid and heat, which seems to 

 weaken the tinplate. This phenomenon is further illustrated by 

 the fact that where- creameries 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 011 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 

 thje iron. This action is accompanied by the evolution of hydro- 

 gen gas, which causes the cans to bulge. This action is hastened 

 by continued exposure of the goods to high temperatures (sum- 

 mer 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, respectively. After sealing, the cans were sterilized 

 in the autoclave, so as to avoid any possibility of bacterial action. 

 After cooling, these sterilized cans were incubated for some time 

 at 90 degrees F. The cans containing the dilute acid began to 

 swell, while the check cans, containing- distilled water only, 

 remained normal. 



Blown Evaporated Milk Due to Change in Altitude. Cans 

 of evaporated milk when filled in factories located at a low 

 altitude (near the sea level) may bulge when transferred to a high 

 altitude. The danger from this source is intensified, if the evap- 

 orated milk happens to be cold at the time of filling, and when the 



1 Hunziker and Wright, Indiana Agricultural Experiment Station. Re- 

 sults not published, 



