Per! PP a 
TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 35 
calculate corresponding curves for the different initial temperatures. 
A series of curves calculated by means of this formula, using one of 
the above experimental curves, will be found to agree closely with 
the other experimental curves starting at different initial tempera- 
tures. The formula is valuable in calculating curves of this sort in 
that it saves much time and labor. 
Figure 21 also shows experimental curves for cooling both in air 
and in water. Attention is directed to the very slow rate of cooling 
in air as compared with that of cooling in water. The form of the 
curves for cans cooled in water are of special interest. In the case 
where the proportion of corn to liquor is the same as in the heating 
curve (that is, 4 to 1) the temperature falls very rapidly at first, 
but later the form of the curve becomes more regular and eventually 
coincides with the second curve. 
In the corn of heavy consistency the lag at the beginning 1 Is greater, 
and the temperature falls more slowly. If the head space in the corn 
se a Ss 
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Se, SenauncSenaeee 
: oS me 
Se eee ee 
° a oar TIME IN MINUTES 
« 6, 
TEMPERATURE IN DEGREES CENTIGRADE 
te 
Fic. 22.—Experimental’ time-temperature curves for ‘‘ Maine style”? corn in No. 2 tin 
cans, Starting at a uniform temperature of 80° C.; processed for different time periods 
at 116° C.; and cooled in air at ordinary room temperature. Proportion of corn to 
liquor, 4:1. The arrows indicate when cans were removed from the retort. Curve 
for can processed : A, For 30 minutes ; B, for 45 minutes; C, for 60 minutes; D, for 
90 minutes, 
of heavy consistency is increased, the cooling will be faster and the 
curve will resemble closely that for the can of corn having a normal 
consistency. At temperatures above 100° C. and where the head 
space permits there. seems to occur a condensation of steam in the 
head space, resulting in a simple sort of distillation which quickly 
reduces the temperature below the boiling point of water. The re- 
duction of the pressure in the head space causes ebullition and a con- 
sequent stirring of the material, resulting in a rapid fall of tem- 
perature. 
These results emphasize again the ct that cooling curves for 
food materials are practically never the exact reverse ae the heating 
curves, even when temperatures of the surrounding medium are re-" - 
versed. 
Figure 22 shows experimental curves for No. 2 cans of corn sealed 
at 80° C. and processed at 116° for 30, 45, 60, and 90 minutes and 
then cooled in the air at 20° to 25° C. 
