10 



MASS. EXPERIMENT STATION BULLETIN 341 



Headspace 

 s 75 cc. 



25 cc. 



Figure 3. 



/^n/w\'^^w^'v^^^^AV^/^/\AVVvAA/vVV«vvv^vwww^^^VvVv^'A^AAft> 



10 20 30 40 50 60 



Time in Minutes 



Pressure Developed in Partially and Fully Sealed Glass Jars Processed in a 

 Water Bath through the Temperature Range of 70° to 212° F. 



The maximum pressure measured in a glass jar during processing in a water 

 bath was 6.86 pounds per square inch. L inferences in time of venting and 

 pressures of duplicate jars are most likely due to differences of bail tensions and 

 variations in covers and rubber cover seats. A lthough the pressure developed 

 in fully sealed jars processed in a water bath is from two to six pounds higher 

 than that developed in partially sealed jars, there has been no experimental or 

 practical evidence yet produced to show that this pressure is in any way 

 dangerous or likely to cause an explosion of the jar. As an added precaution 

 in the use of the Massachusetts method in pressure processing, however, it is 

 advisable to release the pressure in the cooker as slowly as possible. By the 

 time the jar is cool enough to remove from the cooker, the internal pressure has 

 been diminished to such an extent that it is not sufficient to cause any damage 

 even if the jar should crack because of a flaw. 



Fully sealed 

 Partially sealed 



Headspacs 

 25 cc. 

 48 cc. 

 75 cc. 



20 30 40 50 60 



Time In Minutes 



Figure 4. Pressure Developed in Partially and Fully Sealed Glass Jars Processed in a 

 \\;tter Bath through the Temperature Range of 190° to 212° F. 



