12 



MASS. EXPERIMENT STATION BULLETIN 341 



Differences in headspace and in filling temperatures make little difference in 

 the pressure developed. The extent of pressure created in the jars is entirely- 

 dependent on the pressure developed in the pressure cooker, regardless of the 

 type of seal. 



Figure 5. 



10 20 30 40 



Time in fclnutes 



Pressure Developed in Partially and Fully Sealed Glass Jars Processed in 

 Pressure Cooker at 240° F. Filling temperature 180° F. 



HEAT PENETRATION STUDIES ON PARTIALLY AND FULLY SEALED GLASS JARS 



The object of subjecting foods to heat, as previously stated, is to prevent 

 spoilage and to destroy pathogenic microorganisms. The processing time is 

 that which accomplishes the primary object of sterilization but does not 

 seriously impair the plant or animal tissue. Theoretically, the rate of heat 

 penetration should not be affected by fully sealing a jar during processing. 



In order to determine whether any differences exist in the transfer of heat to 

 partially sealed and to fully sealed jars, a series of experiments was conducted 

 using a standardized thermocouple and a Leeds and Northrup Potentiometer 

 Indicator to determine the millivolts indicative of temperature. The results 

 are presented in Figure 6, and show quite clearly that there were no marked 

 differences in the penetration of heat in partially sealed and in fully sealed glass 

 jars of water processed either in a water bath at 212° F. or in a pressure cooker 

 at 240° F. 



