20 



BULLETIN 956, U. S. DEPARTMENT OF AGEICULTUEI 



the time for the processing of No. 2 and No. 3 tin cans of string beans. 

 A, somewhat longer time obviously should be recommended for the 

 glass containers. 



The temperature of the retort or bath is approached in practically 

 the same time whether the processing temperature is 100°, 109°, 116°, 

 or 121° C. Furthermore, the rise in temperature is so prompt that 

 the stirring of the material, as in an agitating cooker, would be of 

 no advantage in distributing the heat throughout the can. 



It is to be understood that the temperature here measured is that 

 of the liquid surrounding the beans. No record was obtained of the 

 actual temperature in the beans themselves, but it would take at most 

 only a few minutes longer for the heat to reach the center of the beans. 



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Fig. 14. — Time-temperature relations for string- beans in 2 per cent brine when processed 

 in quart glass jars at 100°, 109°, 116°, and 121° C. and also when cooled in air. The 

 curves representing the rise in temperature during processing were plotted from read- 

 ings made at intervals of 1 minute ; the curve representing the cooling in air, from 

 readings at intervals oif 1 to 5 minutes. Rise in temperature when processed : 

 A, At 100° C. ; B, at 109° C. ; 0, at 116° C. ; D, at 121° C. a. Fall in temperature 

 when cooled in air at 18° to 22° C. 



Records of the temperature for the cooling, both in air and in 

 water, were obtained. They are very similar to the cooling of dis- 

 tilled water, but are somewhat slower. Here, again, the very great 

 difference in the rate of cooling in air and in water should be empha- 

 sized. When the containers were cooled in water the temperature 

 fell to 30° C. in 10 minutes or less, while it took more than 3 hours 

 to fall to the same temperature in air. In the glass, where a steam- 

 tight closure could not be made, any temperature above 100° C. fell 

 to 100° as rapidly in the container as in the retort, so that the 

 temperature of the glass containers was always 100° when removed 

 from the retort. 



