TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 37 



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cooled in water the maximum temperatures are usually reached at 

 the time when the cans are placed in the water. When cooling 

 immediately in water is practiced one is able to control rather 

 definitely the amount of cooking the corn will receive unless it is 

 of very heavy consistency, when curves such as those shown in figure 

 21 may be of very much value. 



The curves show that when the can is started at 80° C. and processed 

 for 30 minutes at 116° the center of the can of corn never reaches 

 100° C. when cooled 

 in water. When proc- 

 essed for 45 minutes it 

 remains above 100° C. 

 about 13 minutes, about 

 30 minutes when proc- 

 essed for 60 minutes, 

 about 42 minutes when 

 processed for 70 min- 

 utes, and about 60 min- 

 utes when processed 90 

 minutes. It remained 

 above 110° C. for about 

 15 minutes when proc- 

 essed for 70 minutes, 

 and for approximately 

 35 minutes when proc- 

 essed for 90 minutes. 



Differences in initial temperatures and in the consistency of the 

 corn, of course, would vary these figures. 



Figure 24 shows similar curves for corn handled in the same way 

 as in the above tests, except that the retort temperature of 121° C. 

 was employed. 



In the discussion of results obtained with string beans and peas the 

 relationship of the time-temperature and the time-pressure curves 

 was pointed out. In comparing the time-pressure and time-tempera- 

 ture curves in sweet corn it is seen that the pressure rises very rapidly 

 during the first minute or two of the processing period, owing to the 

 heating of the head space. On the other hand, the temperature at 

 the center of the can is still little changed, and the heat certainly has 

 penetrated only slightly into the material. After several minutes, 

 however, the pressure rises more gradually, corresponding closely to 

 the rate at which the heat penetrates into the material. It does not 

 correspond exactly to this, however, for there is a continuous rise of 

 pressure so long as the processing is continued, this being more pro- 

 nounced with the higher processing temperatures. 



Fig. 24. — Experimental time-temperature curves for 

 " Maine style " corn in No. 2 tin cans, starting at a 

 uniform temperature of 80° C, processed for different 

 time periods at 121° C, and cooled in water at 23° 

 to 26° C. Proportion of corn to liquor, 4 : 1. The 

 arrows indicate the time when cans were removed 

 from the retort and placed in water. Curve for can 

 processed : A, For 30 minutes ; B, for 45 minutes ; C, 

 for 60 minutes ; D, for 90 minutes. 



