TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 51 



the temperature changes in the second period. To show clearly the 

 differences that sometimes occur the following experiment was car- 

 ried out. 



Apples, pumpkin, and sweet potatoes were cut into half-inch cubes. 

 These were placed raw in No. 3 tin cans and enough water added to 

 cover the material. Also, soy beans were packed in cans in the same 

 way and enough water was added to cover the material. These were 



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20 *90 



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Fig. 55. — Time-temperature relations for sweet potatoes in various containers when 

 processed for 1 hour on each of three successive days (the intermittent process) at 

 100° C. in the boiling- water bath : A, First day ; B, second day ; C, third day ; a, No. 2 

 tin cans ; h, No. 3 tin cans ; c, pint glass jars ; d, quart glass jars ; x, temperature curve 

 for water bath ; y, temperature curve for room. The interval between the end of the 

 curves in A and the beginning of the curves in B was 18 hours and 40 minutes. The 

 same period of time elapsed between the end of the curves in B and the beginning of 

 the curves in C. 



then processed in the water bath for 1 hour. On the following day 

 they were processed a second time. Figures 56 and 57 show the results. 



In the pumpkin very little difference in the time-temperature 

 curve for the first and second processing is noted. During the first 

 period the rise of temperature was rapid, and it was almost equally 

 so in the second processing. 



In the apples there was a very marked slowing down of the rate 

 of change of temperature, owing to the cooking out of pectin which 

 changed the viscosity of the liquid filling the interspaces. The in- 



