TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 381 
the temperature of the head space at the time of sealing affects the 
vacuum. In this case the head space cooled considerably during the 
few seconds required to transfer the cans from the exhaust box to the 
sealing machine. 
HEAT PENETRATION, 
Figure 19 shows the experimental time-temperature curves for 
tomatoes in No. 2 cans starting at the initial temperature of 30° C. 
and processed at 100° for 20, 25, 80, and 35 minutes and then cooled 
in the air at room temperature, or about 20° C. 
Though the cans were removed from the retort to the air, the tem- 
perature continued to rise for 25 to 30 minutes in the can processed for 
20 minutes, and in the can processed for 35 minutes the rise continued 
for 20. to 25 minutes. If we assume sterilization processes to begin at 
80° C., it will be seen that in the cans processed for 20 and 25 minutes 
the tomatoes at the 
center of the cans did 
not reach the steriliz- 
ing point at any time 
during the process. 
When processed 30 
minutes the tempera- 
ture remained above 
80° C. for 25 to 30 
minutes and when proc- 
Eee desaivirmtniestdesn, “P1519. Sivequpenin cine tenperatare cures for tombe 
about 45 minutes. ture of 30° C., processed for 20, 25, 30, and 35 min- 
These curves ropre- — wer tt 100" G, std then cole In al at oan 
sent the averages for a were taken from the retort. Curve for can processed: 
number of tests. Ow- te Salt hae seat eg 25 minutes; C, for 30 min- 
ing to differences in 
maturity, difficulty in preparing uniform packs, and other factors, the 
time-temperature curves for tomatoes are found to be quite variable. 
It is believed, however, that the average conditions are fairly accu- 
rately illustrated by the above curves. 
These curves show how very limited in usefulness is a time-tempera- 
ture curve established under conditions that carry it entirely to the 
temperature of the retort. It gives very little idea of what temper- 
ature will be reached when processed for a definite time shorter than 
the time necessary to carry the center of the can to the temperature 
of the retort. 
re) 10 20 - 30 40 50 60 70 60 30 100 110 ‘ 12 
TIME IN MINUTES 
TEMPERATURE IN DEGREES CENTIGRADE 
w& 
So. 
t) 
CORN. 
PRESSURE STUDIES. 
The corn used in these tests was gathered in prime table condition 
fresh from the field, husked and silked in the usual manner and cut 
from the cob “ Maine style.” It was then weighed and liquor added 
