TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 45 



very little free liquid, the rate of change of temperature is very slow. 

 In this group are sweet potatoes, sweet corn, pumpkins, and summer 

 squash. Tomato and cabbage form a somewhat intermediate group. 



INTERMITTENT PROCESSING. 



Since sterilization by the intermittent process depends not only 

 upon the maximum temperature attained, but also upon the length 

 of the interval between processing periods and upon the temperature 

 during this interval, it becomes of very great importance to under- 

 stand thoroughly the time-temperature relations throughout the en- 

 tire process. The first processing is supposed to destroy all vegeta- 

 tive forms of bacteria, and during the following interval any spores 

 which may be present germinate and are killed during the second 

 processing period. Any spores failing to germinate during the first 

 interval are expected to germinate during the second interval and so 

 are destroyed in the vegetative form during the third process. If 

 the temperature during these intervals should be either too high or 

 too low for the germination of any spores, then the whole process 

 might fail. It is also known that spores of certain bacteria under 

 optimum conditions germinate very quickly, multiply, and again 

 form spores in a period of less than 24 hours. These facts make it 

 highly important to understand the entire time-temperature rela- 

 tions. 



In the experiments on the intermittent process a record of the 

 processing temperatures, the temperature of the air to which the cans 

 were removed after processing, and the temperature at the center of 

 the can was kept during the entire period of 72 hours. The length of 

 the processing period was exactly 1 hour. This treatment was given 

 once on each of three successive days. String beans, corn, soy beans, 

 and sweet potatoes were tested in this way. 



STRING BEANS. 



The variety of bean used was the Green Pod Stringless. The beans 

 were washed and broken into pieces 1 to 1| inches in length and 

 blanched for five minutes in the boiling- water bath. They were cooled 

 and packed into the cans and enough 2 per cent brine added to cover 

 the material. They were then processed, as above stated. Figure 52 

 shows the results for No. 2 and No. 3 tin cans, and for pint and quart 

 glass jars for the entire period. 



During the first processing the temperature of the No. 2 and No. 3 

 tin cans approached that of the bath in about 10 minutes, the pint 

 jar in about 25 minutes, and the quart jar in 30 minutes. The order 

 of their heating up was No. 2 tin cans first, No. 3 tin cans next, then 

 pint glass jars and quart glass jars last. The No. 2 and No. 3 tin 



