268 UNSWEETENED CoNnbENSED Mink Drricrs 
casein remains in its contracted form and robs the product of its 
original smoothness. 
Blown Evaporated Milk Due to Chemical Action.—\Vhile 
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. [yaporated 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 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 skimmillk and 
return it to the patrons in the milk cans hot, the milk cans aré 
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 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,’ 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. 
