4 BULLETIN 956, U. S. DEPARTMENT OE AGRICULTURE. 



Zavalla (14), in 1916, published tables of experiments with cher- 

 ries, apricots, peaches, and pears. He found the time required for 

 the temperature to reach 212° F. at the center of the can processed in 

 boiling water to vary with the different fruits and explained his 

 findings as due to the difference in their heat conduction. He also 

 stated that the concentration of the sirup seemed to exert a definite 

 action upon the rapidity with which the heat penetrated to the center 

 of the can. His conclusions agree with the results of the present 

 work, but the tables given are not sufficiently clear to make direct 

 comparisons possible. 



Bitting and Bitting (4), using both thermometers and thermo- 

 couples, made numerous tests with various fruits and vegetables 

 (1917) . They worked out experimentally the effect of agitation upon 

 the rate of heat penetration, and found that about 12 revolutions 

 per minute gave the most satisfactory results in getting the heat to 

 the center of the cans without injuring delicate fruits and berries. 

 Numerous diagrams were given, showing the results of processing 

 various substances with the cans held stationary and also rolled. 

 These investigators stated that the minimum time was required to 

 bring the temperature of the can to that of the surrounding bath in 

 those foods in which the proportion of liquid allowed free convec- 

 tion and that mashed sweet potatoes required about the maximum. 

 Furthermore, they found that in sweet potatoes the temperature at 

 the center of the can rarely reaches to within 10 degrees centigrade 

 of that of the retort or bath during the ordinary processing. Their 

 results are entirely in accord with the conclusions drawn from the 

 present work. 



Denton (8) in 1918 reported the results of two tests with carrots 

 in which the influence of closeness of pack on heat penetration was 

 considered. 



During the same year (1918) Bovie and Bronfenbrenner (5) de- 

 scribed a thermoelectric apparatus for measuring the rate of heat 

 penetration in foods during the canning process. The apparatus 

 allowed the determination of the temperature at various parts of the 

 can at any time during the processing by means of thermocouples. 

 Measurements closer than 1° C. were not attempted, however, and 

 the " constant " junction was placed in the autoclave close to the 

 test can. Inasmuch as 15 minutes were required to obtain an equi- 

 librium of pressure and therefore temperature, the " constant " junc- 

 tion did not become constant until 15 minutes after the can was placed 

 in the retort. 



While this apparatus would be satisfactory, perhaps, for sub- 

 stances like baked beans and sweet potatoes, it would be entirely 

 unsuited for the determination of temperature changes in cans of 

 such products as string beans and peas, in which the temperature in 



