TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS 4] 
peratures and processed at 116° C., are shown in fieure 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 erdinarily handled. Regardless of 
initial temperature, the temperature of the retort is reached in the 
same time. 
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200 
TEMPERATURE IN DEGREES CENTIGRADE 
TIME IN MINUTES 
Fic. 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° C. 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 253° C.; B, at 40° C.; C, at 51° C.; D, at 
wie teeter On, i at O° C.s G, at 90° C.; X, at 116° C. and cooled in air at 
46° .-C.'3 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-cishths 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 
