TEMPEBATUBE CHANGES, ETC., DTJBING CANNING OPEBATIONS. 31 



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, 30, 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- 

 essed 35 minutes for 

 about 45 minutes. 



These curves repre- 

 sent the averages for a 

 number of tests. Ow- 

 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. 



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 



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 7(f 

 6tf 

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Fig. 19. — Experimental time-temperature curves for toma- 

 toes in No. 2 tin cans, starting at a uniform tempera- 

 ture of 30° C, processed for 20, 25, 30, and 35 min- 

 utes at 100° C, and then cooled in air at ordinary 

 room temperature. The arrows indicate when cans 

 were taken from the retort. Curve for can processed : 

 A, For 20 minutes ; B, for 25 minutes ; C> for 30 min- 

 utes ; D, for 35 minutes. 



