2 BULLETIN 956, U. S. DEPARTMENT OF AGRICULTUEE. 



be maintained long enough to render all microorganisms harmless. 

 Before an accurate judgment as to the proper cooking period can be 

 ; formed it is necessary to know how long a time is required for the 

 food at the center of the container to reach the temperature of the 

 retort or water bath in which it is being processed. 



In the work here reported upon attention has been centered upon 

 these time-temperature relations, and the purpose has been to bring 

 to light underlying principles rather than to lay down definite rules 

 of procedure, for specific recommendations should be preceded by 

 carefully demonstrated facts. 



The diagrams and other data presented are based upon the results 

 of more than 600 tests made during the year 1919. All vegetables 

 used were grown especially for this work on the experimental farm 

 at Arlington, Va., and these, together with such fruits as were used, 

 were handled fresh from the fields. In the details of preparation 

 of these materials for the tests, no attempt was made to follow any 

 particular set of rules hitherto laid down. Rather, an endeavor was 

 made to illustrate average conditions, and the results of this experi- 

 mentation are offered in the hope that they may be of service to 

 other workers in this field. 



REVIEW OF THE LITERATURE. 



Attention was first called to the importance of the rate of heat 

 penetration into cans of food material during processing by Prescott 

 and Underwood (12, T)^ in 1898. In a study of the cause of souring 

 in canned corn these authors went thoroughly into the bacteriology 

 of the problem and isolated and studied the causal organisms found. 

 A long series of experiments was undertaken involving more than 

 400 tests, in which, by the use of maximum thermometers sealed into 

 the cans, the length of time required for the temperature at the center 

 of the cans of corn to reach that of the retort was determined. Their 

 results showed that, whatever the temperature of processing, the 

 center of the cans of corn reached the temperature of the retort in 

 approximately the same time. This observation has been made by 

 later investigators and accords with the findings reported in this 

 work. 



These workers found that in processing corn at 118.8° C. for 1 

 hour 55 minutes were required for the center of the 2-pound can to 

 reach the temperature of the retort, and they concluded that in 

 processing for 1 hour the maximum temperature was maintained for 

 only 5 minutes. They failed to take into consideration, however, the 

 fact that in substances of heavy consistency, such as corn, the tem- 

 perature is maintained for a considerable time at or very close to the 

 temperature of the retort after removal from it to the air. 



2 Serial numbers in parentheses refer to " Literature cited " at the end of this bulletin. 



