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. 



PBESSURE STUDIES. 



The tests upon tomatoes varied from those upon other substances 

 in that the time-pressure curves were determined after different ex- 



8 





















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Eig. 17. — Experimental time- 

 pressure curves for toma- 

 toes in No. 2 tin cans, show- 

 ing the effect of different 

 periods of exhaust upon 

 pressures developed during a 

 processing period of 45 min- 

 utes at 100° C. Curve for 

 can : A, Receiving no ex- 

 haust ; B, exhausted for 2 

 minutes at 100° C, before 

 processing ; C, exhausted 

 for 4 minutes at 100° C, 

 before processing ; D, ex- 

 hausted for 6 minutes at 

 100° C, before processing. 



D 



Fig. 18. — Experimental time-pres- 

 sure curves^ for tomatoes in No. 

 3 tin cans, showing the effect of 

 different periods of exhaust upon 

 pressures developed during the 

 processing period of 45 minutes 

 at 100° C. Curve for can : A, 

 Receiving no exhaust ; B, ex- 

 hausted for 2 minutes at 100° C, 

 before processing; C, exhausted 

 for 4 minutes at i00° C, before 

 processing ; D, exhausted for 6 

 minutes at 100° C, before proc- 

 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. 



