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 oeneral guide in the selection of the 
most desirable sealing tem- 
peratures. 
Relation of time to pres- 
Saas sl veal ig OLA bs roo] ai 
sure changes—The relation ere Se ee 
of time to the pressure 
changes during processing is Te 
illustrated in figure 4, which 2, eae 
shows the time-pressure pap 
curves obtained for the No. : aint olorilol se pen ALLY Vins: (| 
Se aaietiae BOQ) GC. H¢: 0 a a ble OY 
Attention is directed espe- aca ea) 
cially to the steepness of the aS ee 
curves during the first min- ee een 1a ae 
ute of the processing and to estes ds, lea Y OA wuliae aban 
the fact that the pressure ~ 
shortly reaches an_ equilib- a 
rium. The close correlation « // 
of the pressure changes and KX 77a 
time-temperature changes in Ae | Vas. (esd ssl | ka 
the ean is clearly shown. The i: TEMPERATORE, ch DEcnres CENTIGRADE 
comparison of the form of Fic. 5.—Theoretical vacuum curves for a non- 
i : h k contractile can containing air and sufficient 
these curves with the curves water to give saturation when sealed at dit- 
sy 
oc 
PRESSURE IN INCHES OF MERCURY 
for the various food mate- ferent uniform temperatures and read at 0°, 
oer 3 L0°s 20°,. 80°, and 40° €.°: Calculations’ are 
rials shown later will be based upon mean barometric pressure. Curve 
found of much interest. for readings made: A, At 402 [CRs By ate sOR 
G20; at 20° CD) at. 10° Cin, at OeN a. 
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. 
