08 a 
TEMPERATURE CHANGES, ETC., DURING CANNING OPERATIONS. 29 
of liquor has not been added the rate of change of temperature will 
be slightly slower. These differences are usually insignificant in 
common practice, in so far as such variations affect the length of the 
, - 
processing period. 
TOMATOES. 
PRESSURE STUDIES. 
The tests upon tomatoes varied from those upon other substances 
in that the time-pressure curves were determined after different ex- 
pressure IM POUNDS PER SQUARE INCH 
P) 50 
TIME IN MINUTES 
Fic. 17.—Experimental time- i es hae Sey reli ae 
pressure curves for toma- Fig. 18.—Experimental time-pres- 
toes in No. 2 tin cans, show- sure curves for tomatoes in No. 
ing the effect of different 
periods of exhaust upon 
pressures developed during a 
processing period of 45 min- 
3 tin cans, showing the effect of 
different periods of exhaust upon 
pressures developed eduring the 
utes at 100° C. Curve for processing period of 45 minutes 
can: A, Receiving no ex- at 100° Ci Curve, for. can: As 
haust; B, exhausted for 2 Receiving no exhaust; B, ex- 
minutes at 100° C., before hausted for 2 minutes at 100° C., 
processing; C, exhausted before processing; C, exhausted 
for 4 minutes at 100° C., for 4 minutes at 100° C., before 
before processing; D, ex- processing; D, exhausted for 6 
hausted for 6 minutes at minutes at 100° C., before proc- 
100° C., before processing. essing. 
haust periods. The tomatoes were peeled without scalding and 
weighed directly into the test cans, 550 grams being used in the No. 
2 and 950 in the No. 3 cans. The initial temperature in all cases was 
between 22° and 25° C. The brass attachment was soldered to the 
can, which was then placed in the retort in the usual manner. In 
the case of the can receiving no exhaust, sealing was effected im- 
mediately and the test begun. The processing in all cases was at 100° 
C. In succeeding tests after placing the cans in the retort the steam 
was turned on and as soon as the retort temperature reached 100° 
C. (which was close to 30 to 45 seconds), time was taken and the 
cans exhausted for 2, 4, and 6 minutes, respectively. At the end of 
the exhaust period the can was immediately sealed, as previously de- 
scribed, and the time-pressure figures obtained. 
Figure 17 shows the curves obtained for the No. 2 and figure 18 
those for the No. 3 cans. 
