24 BULLETIN 1022, U. S. DEPARTMENT OF AGRICULTURE. 
Figure 12 shows curves for a No. 2 can of beans not packed so 
closely as in the test cans of figure 10, but pice £002, CiGee 
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 apenas of 20° C. is shown. 
A study of the foregoing curves shows that the retort temperature 
is reached only shghtly 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 
140; 
120 
g 
8, 
TEMPERATURE IN DEGREES CENTIGRADE 
~I 
O, 
TIME IN MINUTES 
Fic. 12.—Experimental time-temperature curves for No. 2 eans of string 
beans, starting at different uniform temperatures and processed at 
different temperatures. Curve fer 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° €. and processed at 100° C.; 
Gc, at 80° C. and processed at 116° C.; c’, at 80° C. and processed at 
a 2Ao @: 
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 
ereater 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 
