TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 41 



peratures and processed at 116° C, are shown in figure 27. Experi- 

 mental curves for cooling both in air and in water are likewise given. 

 The heating curves are similar to those for corn, though there is a 

 greater lag at the start and the temperature reached in a given unit 

 of time is materially lower than in the corn. In other words, as has 

 been previously shown, the rate of temperature change is slower in 

 sweet potatoes than in corn, as ordinarily handled. Regardless of 

 initial temperature, the temperature of the retort is reached in the 

 same time. 









































































1 » 













110° 

 100° 



a 90° 



£80° 



£70° 

 S60" 



I 50 " 

 1 















\z 



V 





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^"E 











































/T> } 











































yi. 











































/& 









































30° 





A 



















































































20° 



































































































■> 2 



3 



5 4 



5 



t> 6 



3 7 



J a 



3 



IC 



1 



6 i 



10 1 



M 



15 



1 



o n 



o le 



O 19 



O 20 







"Fig. 27. — Experimental time-temperature curves for sweet potatoes in the form of pie 

 stock in No. 2 tin cans, starting at different uniform temperatures and processed at 

 116° G. Curves are given also for cooling in air and in water at 26° C. A curve 

 showing the effect of differences in head space upon the rate of cooling in water is 

 included. Curve for can starting: A, At 251° C. ; B, at 40° C. ; C» at 51° C. ; D, at 

 61" C. ; E, at 70° C. ; F, at 80° C. ; G, at 90° C. ; X, at 116° C. and cooled in air at 

 26° C. ; Y, at 116° C. and cooled in water at 26° C, head space very small ; Z, at 116° C. 

 and cooled in water at 26° C, head space three-eighths of an inch. 



Here, also, as in the case of the curves for corn, the formula 

 given by Thompson (9) for the calculation of curves for different 

 initial temperatures from a single experimental curve is applicable, 

 and the formula given by Bigelow and his collaborators for calcu- 

 lating curves for cans of different sizes may be made use of in time- 

 temperature studies with sweet potatoes. 



As has been pointed out in the consideration of time-temperature 

 relations in corn, curves which require a longer time to reach retort 

 temperature than that necessary to effect sterilization of the product 

 are not safe guides in the determination of proper processing 

 periods, inasmuch as when cooled in air and, in the case of sweet 



