TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 39 



bath, and then removed immediately to the air. The temperature 

 at the center of the can continues to rise for 20 to 30 minutes after 

 it is put in the air. When the can is processed for 1 hour at 121° 

 the temperature just approaches 100° C. If the can had been left 

 in the retort instead of being put in the air, the temperature would 

 have gone higher. This shows again the importance and necessity 

 of knowing what temperatures are reached during the {processing 

 period. Such factors as these are often overlooked, when they are 

 of very great importance. If the initial temperature had been dif- 

 ferent, it would have affected the maximum temperature attained. 

 In processing sweet potatoes in No. 3 tin cans it is of very great 

 importance to have the initial temperature as high as practicable. 



TOMATOES. 



The tomatoes used in these tests were of a special disease-resistant 

 variety being studied at the Arlington Experimental Farm. They 

 were fully ripened 

 and of medium size. 

 After scalding for 

 two minutes in boil- 

 ing water they were 

 plunged into cold 

 water to be peeled. 

 After peeling they 

 were packed into 

 the cans as nearly 

 whole as possible. 

 No water or other 

 liquid was added. 

 Tests in both tin 

 and glass containers 

 were made, as usual. 

 Cooling tests in air 





so so w 



/OO //O /20 /30 /40 



Fig. 45. — Time-temperature relations for tomatoes when 

 processed in No. 2 tin cans at 100°, 109°, 116°, and 

 121° C. These curves were plotted from readings 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. 



only were made. 

 The temperature of 

 the air varied considerably, so that the cooling in the various tests 

 is not strictly comparable, and the curves were therefore omitted 

 from the charts. The results showed, however, that the cooling 

 would be somewhat slower than for string beans. Figures 45 to 48 

 show the results of these tests. Individual curves represent tests of 

 a single can. Duplicate cans varied considerably, owing perhaps to 

 inability to pack them exactly alike. The curves illustrate average 

 results quite well, however. 



The rate of change in temperature is faster than in pumpkin or 

 sweet corn, but very much slower than in string beans. At 100° C. 



