24 



BULLETIN 1022 TJ. S. DEPARTMENT OF AGEICULTUEE. 



Figure 12 shows curves for a No. 2 can of beans not packed so 

 closely as in the test cans of figure 10, but processed at 100°, 116°, 

 and 121° C. 



Figure 13 is the same for a No. 3 can, and in addition the curve 

 for cooling in water at the constant temperature of 20° C. is shown. 



A study of the foregoing curves shows that the retort temperature 

 is reached only slightly sooner in the No. 2 can sealed at 80° than in 

 the can sealed at 20° C. and that the effect of differences in initial 



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Fig. 12. : — Experimental time-temperature curves for No. 2 cans of string 

 beans, starting at different uniform temperatures and processed at 

 different temperatures. Curve for can starting : A, At 21° C. and 

 processed at 100° C. ; a., at 23° C. and processed at 116° C. ; a', at 23° 

 C. and processed at 121° C. ; C, at 80° C. and processed at 100° C. ; 

 c, at 80° C. and processed at 116° C. ; c', at 80° C. and processed at 

 121° C. 



temperature is more marked when canning in glass than when can- 

 ning in tin, since the jar starting at 80° requires six or seven minutes 

 less to reach retort temperature than that started at 20° C. 



The differences in the heating curves of cans sealed at the various 

 initial temperatures are of relatively small practical importance in 

 substances like string beans and need be considered only when the 

 minimum processing periods are employed. This accounts for the 

 rather uniform results obtained in some canning practices where the 

 initial temperatures vary considerably. It should be remembered, 

 however, that the total amount of exposure to heat is somewhat 

 greater with the higher initial temperature. 



As previously noted, the time-temperature curves both for the 

 heating and the cooling are similar to those for distilled water, and 



