36 



BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 



These curves represent individual tests and hence probably vary 

 somewhat from the average. They show how the temperature at the 

 center of the can continues to rise after taking from the retort for 

 from 5 minutes in the case of the can processed for 90 minutes to 15 

 minutes in the can processed for 30 minutes. They show, further, 

 the length of time the corn remains above critical temperatures for 

 sterilizing purposes. For instance, the temperature is seen to remain 

 above 100° C. for 20 minutes when the processing is continued for 

 30 minutes and remains above 100° C. for 95 minutes when processed 

 for 90 minutes. These values obviously would be different for curves 

 starting at different initial temperatures. The curves give a definite 

 idea, however, of the rate and the nature of the temperature changes 

 when corn is processed for various periods and then air cooled. They 



show how very limited 

 in value such curves as 

 are illustrated in figure 

 21 may be, for they are a 

 record of a continuous 

 processing at a definite 

 temperature until the 

 temperature of the can 

 reaches the temperature 

 of the retort. Since 

 with corn in actual 

 practice the processing 

 period is less than the 

 time necessary for the 

 can to reach the tem- 

 perature of the retort, 

 curves such as are shown in figure 21 give an actual record only so 

 long as the can is in the retort, but tell nothing beyond that point. 

 It is important to have a record of the temperature after the can is 

 removed from the retort, which can be obtained best from curves 

 made under conditions of actual practice. Since the behavior of the 

 temperature of the contents of the can after removal from the retort 

 varies with the processing period and with the cooling conditions, it 

 makes the calculation of the record of one processing from another 

 of a different length very difficult. 



Figure 23 shows the time temperature curves for No. 2 cans of corn 

 starting at 80° C. processed at 116° for 30, 45, 60, 70, and 90 minutes, 

 and then cooled in water. 



When the cans are removed from the retort and placed in cold 

 water the rise in temperature is almost immediately stopped and the 

 cooling curves drop rapidly. In corn, therefore, when the cans are 



Fig. 23. — Experimental time-temperature curves for 

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

 uniform temperature of 80° C, processed for different 

 periods of time at 116° C, and cooled in water at 

 about 25° C. Proportion of corn to liquor, 4 : 1. The 

 arrows indicate when cans were taken from the retort 

 and put into water. Curre for can processed : JL, 

 For 30 minutes ; B, for 45 minutes ; C, for 60 min- 

 utes ; D, for 70 minutes ; E, for 90 minutes. 



