TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 389 
during this latter half of the processing period indicates that some 
influence other than increase of internal temperature is in operation. 
That this is the case is shown in the vacuum figures given later. 
The maximum pressures attained vary in both directions from the 
theoretical, some being higher and others lower. The variable factors 
of sudden bulging and gradual distention of the cans, liberation of 
gases, etc., contribute to this result and account for it. The swell- 
ing of the starch can 
bavay ecomt tor TT TT TTT TTT 
32 
any increase in pres- 
sure, as the material » 
was well cooked be- x 
fore it was put into 
the cans. 
The processing pe- 
riod used in these ,” 
tests is longer for the 
higher temperatures 
than is commonly em- 
ployed, but the maxi- 
mum pressures for 
any period of 120 
minutes or less will 
be shown on_ these 
curves, for when the 
steam in the retort is 
cut off the pressures 
fall almost immedi- 
ately. TIME are MINUTES 
° ° Fic, 26.—Experimental time-pressure curves for sweet pota- 
As pointed out in toes in the form of pie stock in No. 3 tin cans, 
considering the re- sealed at different uniform temperatures and processed 
. for 2 hours at 100°, 116°, and 121° C. Curve for can 
sults on string beans, sealed: A, At 25° C. and processed at 100° C.; a, at 
the actual strain on 25° C. and processed at 116° C.; a’, at 25° C. and proc- 
: essed at 121° €C.; B, at 70° C. and processed at 100° C.; 
cane at any time dur- b, at 70° C. and processed at 116° C.; b’, at 70° C. and 
ing the process may processed at 121° C.; C, at 80° C. and processed at 
be found by subtract- 209,056, 80" Sand proceed at 110" 0. ea 
ing the retort pres- 
sure from the pressure indicated for that time in the curve. 
The strain on the can is greatly increased when the retort 
pressure is released, but the greatest strain is felt when the pres- 
sure in the retort reaches zero. This amounts to only about 3 to 
5 pounds less than the maximum pressure indicated in the curves, 
depending upon the temperature of sealing, the processing tempera- 
ture, the bulging of cans, the rate of release of retort pressure, etc. 
If the retort pressure should be completely released instantaneously 
PRESSURE IN POUNOS PER SQUARE INCH 
cS 
