TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 41 



tures. There is very little starch, pectin, or other readily soluble 

 colloidal material in the tomato. It consists of organic acids 

 and sugars, with insoluble cell tissues and a large amount of water. 

 As a high temperature is reached the tissues begin to collapse, leav- 

 ing a free liquid in which convection can take place. This explains 

 the greater rate of temperature change at the higher processing 

 temperature than at the lower. 



Such high temperatures as 109°, 116°, and 121° C. are not neces- 

 sary for the sterilization of the tomato, and the results are only of 

 theoretical interest. Where it is of importance to keep the tissues 

 of the material intact high temperatures should be avoided. It is 

 of interest and impor- 

 tance to know just what 

 temperatures are reached 

 when the various cans 

 are processed for 10, 15, 

 20, 25, 30, and 40 minutes 

 each, but this work has 

 not yet been completed. 



The irregularities 

 noted in the curves for 

 tomatoes in the glass con- 

 tainers are due to the 

 tendency of the material 

 to rise to the top when it 

 collapses under the high 

 temperatures. The solid 

 portion as it rises may 

 for a time surround the 

 thermometer, preventing 

 convection, but later rises still higher, leaving the bulb of the ther- 

 mometer in a liquid that is more or less free. 







£. 



IS: 



Fig. 48. — Time-temperature relations for tomatoes 

 when processed in quart glass jars at 100°, 109°, 

 116°, and 121° C. These curves were plotted from 

 reading's made at intervals of 5 minutes. Rise in 

 temperature when processed : A, At 100° C. ; B, at 

 109° C. ; C, at 116° C. ; D, at 121° C. 



CABBAGE. 



All cabbage plants used in these tests had firm heads, and the 

 outer leaves were discarded. The heads were sliced somewhat 

 coarser than for sauerkraut, with a rotary slicing machine. The 

 sliced material was then blanched in flowing steam for 10 minutes, 

 after which it was packed into the cans and enough water added to 

 fill the interspaces. The results are shown in figures 49 and 50. 

 The wide variation is due to inability to pack the cans exactly alike. 

 In general when packed in this way the rate of change of tempera- 

 ture at the center of the can is very much slower than that of string 

 beans, but considerably faster than that of sweet corn. Cabbage is the 



