STERILIZATION. 15 



DETERMINATION OF TEMPERATURE AND TIME OF PROCESSING. 



In sterilizing, the heat must be applied equally to all cans, and it 

 is therefore necessary to deliver steam at the bottom of the kettle, 

 whether open or in a retort, to insure a circulation of the heat. In 

 retorts, whether steam or hot water is used, there must always be a 

 vent open to give off steam in order to hold the heat uniform at all 

 points. The thermometer is the all-important tester, for if it does 

 not show the proper degree of temperature, spoilage will follow. To 

 test the uniformity of temperature in a retort, self-registering ther- 

 mometers are sealed in a number of cans when placed in the crates, 

 the cans are marked, and when the cooking is completed the ther- 

 mometers are examined and compared, so that the heat may be 

 adjusted until all give like readings. In a similar manner the time 

 required for the heat to reach the center of the can is obtained, experi- 

 mental lots being run for varying periods, and the temperature noted. 

 The calcium chlorid or oil bath acts in the same way as the open 

 water bath. 



The writer employs two methods of determining the temperature 

 in the center of a can and the rate of penetration. First, a ther- 

 mometer is placed in a packing joint which is soldered into the can 

 so that the bulb will just reach the center. By placing a collar an 

 inch above the gasket the can may be submerged in oil and heat 

 applied until a certain temperature is reached. The length of time 

 necessary for the thermometer inside the can to reach the same point 

 as that on the outside, or within from 2 to 5 of it, as experience 

 demonstrates may be sufficient, must be allowed in the retort and the 

 heating then continued for such an interval as may be found neces- ' 

 sary for sterilization. For example, if the spores of certain organ- 

 isms are killed at 230 F. in 12 minutes, and it should take 20 minutes 

 to cause the content of the can to become heated, it would require 32 

 minutes as a minimum for processing, and as a margin of safety the 

 recommendation would be for a longer time, probably for 40 minutes. 



The second method of determining temperature in different parts 

 of the retort and in the center of cans is to seal a thermocouple in the 

 can and connect it with a recording apparatus. Thus a time and 

 temperature curve is obtained directly. One of the important points 

 learned from the latter apparatus was the effect of stirring or agitat- 

 ing the contents of cans which ordinarily required long cooking. A 

 can of corn in a retort requiring 65 minutes to reach 245 F. requires 

 only 30 minutes when rolled back and forth. The effect of the agi- 

 tation was a shorter cooking, a brighter color of the corn, and a bright 

 can on the inside. The principle is good, but some mechanical diffi- 

 culties in successful operation have yet to be overcome. 



