166 CONCENTRATED MILK 
If held in the factory, it should be placed in a cold room or 
should be otherwise protected against temperatures sufficiently 
high to cause if to sour. When kept at 40 degrees F. or below 
the danger from souring is largely eliminated. If transported 
long distances during warm weather, it should be shipped in 
refrigerator cars. 
Ciuapter NII. 
CONCENTRATED MILK. - 
Definition.—Concentrated milk is cow's milk, either whole 
milk, or partly or wholly skimmed milk, condensed at the ratio 
of three to four parts of fresh milk to one part of concentrated 
milk. It is not condensed in vacuo, but in open vats by passing 
currents of hot air through the milk. It is sold largely in pint 
and quart bottles for direct consumption. It is not sterile and 
therefore keeps for a limited time only. Its keeping qualhty is 
similar to that of a high grade of properly pasteurized milk. The 
process by which the concentrated milk is manufactured is 
known as the “Campbell Process.” This process was invented 
by J. H. Campbell of New York City, in 1°CO and patented in 
1901. 
Apparatus Needed — The principal parts are: the evapo- 
rating vat with hot water jacket and coils, and air blast regis- 
ters or nozzles near the bottom of the vat; an air blower which 
furnishes the air blast; an air heater through which the air 
blast passes and from which the heated air is conducted into the 
milk; a water pump circulating het water through the jacket 
and coils; an auxiliary evaporating tank for completing the 
evaporation; and a spray pump which throws the spray of milk 
drawn from the bottom of the main evaporating vat into the 
auxiliary tank and for transferring the partly condensed milk 
from tank | to tank 2. 
Operation of Campbell Process.—'lhe milk is heated to about 
ICO degrees F. and allowed to How into evaporating tank 1, 
\Water at temperatures ranging from 100 to 125 degrees F. is 
forced through the coils and jacket. Hot air is then passed into 
the milk. ‘The temperature of the air is regulated so as to keep 
the temperature of the evaporating milk down to 120 degrees F. 
