18 



BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 



tests, using No. 3 cans sealed at different temperatures and processed 

 at 116° C. 



The temperature of the retort is reached only one to one and one- 

 half minutes sooner when the initial temperature is 80° than when it- 

 is 20° C. A comparison of these curves with similar ones for different 

 food substances shown later will be found to be of interest. Cooling 

 curves are also shown for the No. 3 can cooled from 116° in water 

 at constant temperature to 60° and 20° C, respectively. While, as 

 in the heating, the temperature changes within the can take place very 

 rapidly, the heating and the cooling curves are not the exact reverse 





































































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Fig. 6. — Experimental time-temperature curves for distilled water in No. 3 tin cans, 

 starting at different uniform temperatures and processed at 116° C. The heating 

 curve is shown for a can starting at 20° C. and processed at 100° C. ; and curves 

 showing the rate of cooling in water at different temperatures. Curve for can starl- 

 ing : A, At 20° C. and processed at 100° C. ; B, at 20° C. and processed at 116° C. ; 

 C, at 40° C. and processed at 116° C. ; D, at 60° C. and processed at 116° C. ; E, at 

 80° C. and processed at 116° C. ; F, at 100° C. and processed at 116° C. ; O, at 110° 

 C. and processed at 116° C. ; X, at 116° C. and cooled in water at 60° C. ; Y, at 116° 

 C. and cooled in water at 20° C. 



of each other. This is due in part, of course, to the fact that the 

 viscosity of water changes with changes in temperature. As the 

 temperature in the can approaches the temperature of the cooling 

 bath there is a flattening out of the curve, due in part to the increase 

 in viscosity of the water, which is much more marked than in the 

 corresponding portion of the heating curve, where the viscosity is 

 continuously diminishing and the time required to effect the complete 

 change is materially lengthened. 



Figure 7 shows the rate of temperature change at the center of a 

 quart glass jar with water sealed at different temperatures and pro- 

 cessed at 100° G. 



