TEMPERATURE CHANGES IN CANNING FRUITS AND VEGETABLES. 11 



tight closure could not be made, owing to the inability of the glass 

 to stand steam pressure. 



Figure 3 shows the curves representing the temperature changes 

 during the processing period and also the cooling in air and in 

 water. These represent the averages of six tests for the rise in tem- 

 perature during processing, but the cooling in water and in air are 

 the averages of only three tests. The temperatures of the air and 

 of the water in the different cooling tests varied somewhat, so that 

 the curves are not absolutely uniform. The initial temperature was 

 20° C. The temperature of the water in which the cooling was done 

 varied between 15° and 18° C. It is seen that the change in tem- 

 perature at the center of the can is exceedingly rapid when the can 



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Fig. 3. — Time-temperature relations for distilled water when processed in various con- 

 tainers at 100° C. The curves representing rise in temperature during processing and 

 the fall in temperature during cooling in water were plotted from readings made at 

 intervals of 30 seconds ; curves representing cooling in air, from readings at intervals 

 of 5 to 10 minutes. Rise in temperature : A, In No. 2 tin cans ; B, in No. 3 tin cans ; 

 C, in No. 10 tin cans ; B, in pint glass jars ; E, in quart jars. Cans cooled in 

 water: a', No. 2 at 17° C; &', No. 3 at 16° C. ; & ', No. 10 at 16|° C. Cooled in air: 

 a, No. 2 cans at 17° to 20° C. ; h, No. 3 cans at 16° to 20° C. ; c, No. 10 cans at 16° 

 18° C. ; d, pint glass jars at 16° to 18° C. ; e, quart glass jars at 18° to 20° C. 



is plunged into the water bath at 100° C. In the No. 2 tin can the 

 temperature of the bath is approached in about eight minutes. It is 

 also noted that the No. 3 can is only slightly slower than the No. 2, 

 requiring only two or three minutes longer to attain the temperature 

 of the bath. The No. 10 tin can is somewhat slower than the No. 3, 

 but even here the temperature at the center approaches that of the 

 retort in 15 minutes. The temperature changes in the glass con- 

 tainers are very much slower than in the tin, requiring about 20 

 minutes for the temperature of the center of the pint jar to approach 

 that of the water bath, and about 27 minutes for the quart jar to 

 reach the same temperature. There is thus a very marked retarda- 

 tion in the glass. When the tin containers are removed from the 

 boiling water bath and placed in water at 17° C. there is a very 



