TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 11 



sealed at various temperatures and processed at 100°, 109°, 116°, and 

 121° C. These are calculated for the mean barometric pressure. 



These curves show how relatively great pressures are developed 

 when containers are sealed at the low temperatures and bring out 

 clearly the fact that when the sealing temperature is increased the 

 pressures are not reduced in the same proportion, but fall off with 

 increasing rapidity as the sealing temperature of 100° C. is ap- 

 proached. They also serve as a general guide in the selection of the 

 most desirable sealing tem- 

 peratures. 



Relation of time to pres- 

 sure changes. — The relation 

 of time to the pressure 

 changes during processing is 

 illustrated in figure 4, which 

 shows the time-pressure 

 curves obtained for the No. 2 

 can containing 550 c. c. of 

 water. 



Attention is directed espe- 

 cially to the steepness of the 

 curves during the first min- 

 ute of the processing and to 

 the fact that the pressure 

 shortly reaches an equilib- 

 rium. The close correlation 

 of the pressure changes and 

 time-temperature changes in 

 the can is clearly shown. The 

 comparison of the form of 

 these curves with the curves 

 for the various food mate- 

 rials shown later will be 

 found of much interest. 

 Sharp breaks in the curves, 

 as in the others which follow, show where the sudden bulging of the 

 cans occurred. 



Theoretical vacuum curves. — Of equal, if not of greater impor- 

 tance, is the matter of vacuum obtained as the result of various can- 

 ning operations. Here, again, theoretical figures serve as a back- 

 ground for experimental work and furnish information of much 

 practical value. Figure 5 shows the theoretical vacuum curves for 

 a noncontractile receptacle containing air and saturated vapor when 

 sealed at various temperatures and cooled to the uniform tempera- 

 ture of 0°, 10°, 20°, 30°, and 40° C. These are calculated on the basis 

 of mean barometric pressure. 



























































































































































- 













































































































































































c /a j 





























































n ( 





r 2 









r e 



O- 7 



O" 8 





o" K 





TEMPERATURE IN DEGREES CENTiGBAOE. 



Fig. 5. — Theoretical vacuum curves for a non- 

 contractile can containing air and sufficient 

 water to give saturation when sealed at dif- 

 ferent uniform temperatures and read at 0°, 

 10°, 20°, 30°, and 40° C. Calculations are 

 based upon mean barometric pressure. Curve 

 for readings made : A, At 40° C. ; B, at 30° 

 C. ; C, at 20° C. ; D, at 10° C. ; E, at 0° C 



