TEMPERATURE CHANGES IX CANNING FRUITS AND VEGETABLES. 33 



variety used in these tests was Stowell's Evergreen. The corn was 

 prepared in the Maine style, placed in No. 2 tin cans, and processed at 

 100° C. The proportions of corn to liquor used in these tests were 

 1 to 0, 1 to 1, 2 to 1, 3 to 1, 4 to 1, and 5 to 1. The results are shown in 

 figure 36, 



In the can having the proportion of 1 to 1 there is a very rapid 

 rise in temperature, due largely to convection which occurs in the 

 liquid. The last two or three degrees go very slowly, however, owing 

 to gelatinization of the starch, which increases the viscosity to such 

 an extent as to counteract the force, small at this point, tending to 

 cause convection. In the can having the proportion of 2 to 1 there is 

 a marked falling off in the rate throughout the curve. There is con- 

 siderable convection here, but it is less pronounced and stops sooner 

 than in cans having the proportion of 1 to 1. Likewise in the 4 to 1 

 and in the 5 to 1 there is 

 a further falling off of 

 the rate of temperature 

 rise. In these cans con- 

 vection is further re- 

 duced and probably plays 

 only a small part in the 

 5 to 1 cans. It is noted 

 that the temperature at 

 the center of the can ap- 

 proaches that of the bath 

 more cjuickly in the case 

 of the corn alone than in 

 the proportion of 5 to 1, 

 4 to 1. or 3 to 1. This 

 apparent inconsistency is 

 easily understood when 

 one realizes what is taking place m the four cans. In the can 

 having the proportion of 5 to 1 there is little, if any, convection, 

 for tlie going into solution of the starch forms a mass having so 

 small an amount of free liquid that very little or no convection takes 

 place. In the proportion of 4 to 1 some convection occurs, but it is 

 checked early in the process by the same cause. The same in general 

 is true in the case of 3 to 1, but more time is required to arrest the 

 convection currents. In the corn alone there is no free licjuor in 

 which convection can take place, but there is a saturated air more or 

 less continuous from the center to the outside of the material, which 

 certainly allows some convection, thus accounting for the more i-ai)id 

 rise in the corn alone than in the 4 to 1 and the ") to 1 cans. If the 

 matei'ial in the can of corn alone had been i)acked down tightly the 

 curve would have been consideiablv different. 



— [ I - y~ 



ki 60 

 4W 



*" /O 20 >30 ■fO £0 60 70 so so /OO //<? /eO 



Fio. 3G. — Time-temperature relations; for sweet corn 

 (Maine style) with different proportions of liquor 

 processed in No. 2 tin cans at 100° C. These 

 curves were plotted from temperature readings 

 made at intervals of 5 minutes. Proportion of 

 corn to liquor : .1 , 1 : 1 : ii. i; : 1 : C. ". : 1 ; />, 4 : 1 ; 

 B, 5:1; F, corn alone. 



