TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 47 



Curves of this sort would vary in form and in the maximum tem- 

 peratures reached, of course, with different retort temperatures and 

 with the length of the processing periods. 



In figures 34 and 35 are shown the effect of different exhaust periods 

 upon the time-temperature curves for No. 2 and No. 3 cans of sweet 

 potatoes sealed at different temperatures, processed for 60 minutes, 

 and cooled in air. Exhausting was done in the steam box for 5, 10, 

 and 15 minutes at 100° C. 



The effect of exhaust upon the form of the curves and the maxi- 

 mum temperatures reached are clearly shown, and little comment 

 is required. It may be pointed out that in the case of the No. 2 cans 

 the temperature in all cases went above 100° C. ; 15 minutes' exhaust 

 resulted in the temperature remaining above 100° C. for 18 to 20 

 minutes longer than in those receiving no exhaust. The maximum 

 temperatures varied by 4 or 5 degrees. 



















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Pig. 35. — Experimental time-temperature curves for sweet potatoes in the form of pie 

 stock in No. 3 tin cans, starting at different uniform temperatures, exhausted for 

 different time periods at 100° C, processed for 1 hour at 116° C, and cooled in air 

 at ordinary room temperature. Curve for can, starting : A, At 26° C. and receiving 

 no exhaust ; B, at 26° C. and exhausted for 5 minutes ; C, at 26° C. and exhausted for 

 10 minutes; D, at 26° C. and exhausted for 15 minutes; E, at 53° C. and receiving 

 no exhaust ; F, at 53° C. and exhausted for 5 minutes ; G, at 53° C. and exhausted for 

 10 minutes ; H, at 53° C. and exhausted for 15 minutes. 



It is noted also that the time-temperature curve for the No. 2 can 

 starting at 26° C. and exhausted for 15 minutes coincides almost 

 ■exactly with that for the can sealed at 52° with no exhaust. 



As is to be expected, the differences are greater in the case of the 

 No. 3 cans. In only three, of the cans did the temperature at the 

 center of the containers reach 100° C. The maximum temperatures 

 reached in cans exhausted for 15 minutes varied from those receiv- 

 ing no exhaust by 4 or 5 degrees, and, as in the case of the No. 2 can, 

 the effect of the 15-minute exhaust on the increase in the length of 

 time the temperature remained above a definite point amounted to 

 18 or 20 minutes. 



