4 MASS. EXPERIMENT STATION BULLETIN 341 



THE PROBLEM 



There is often a marked loss of liquid from jars processed in the customary 

 partially sealed condition, referred to in this bulletin as "vent loss." This loss 

 is much greater in steam-pressure processing than in water-bath processing. 

 Fully sealing the jars prior to heat processing tends to alleviate this undesirable 

 condition and eliminates the necessity of handling the hot wire bails and jars 

 immediately after removal from the processing tank. (See Plate I.) 



Although commonly called "fully sealed" when the bail is in the high tension 

 position, this term is technically a misnomer because, when sufficient pressure 

 is developed within the container, the glass cover will lift slightly permitting a 

 release of the expanding gases and vapors as in the partially sealed condition. 



LABORATORY EXPERIMENTS 



VFNT LOSSES DURING HEAT PROCESSING 



The noticeable loss of liquid in partially sealed jars processed under steam 

 pressure led to an investigation of vent losses occurring in jars partially and 

 fully sealed, and with varying headspaces and processing periods. 



The calculations of vent losses were made by weighing the jar, cover, rubber 

 ring, wire bail, and water to the required headspace. After the heat processing 

 period was over, the sealed jar was allowed to cool to 70° F. and then reweighed. 

 The difference in weight was due to vent losses during the heat processing 

 period. These data are expressed graphically in Figure 1. 



RAPID RELEASE OF PRESSURE SL0W RELEASE OF PRESSURE 



Loss of Liquid in Grams 

 25 50 75 100 25 



Headspace 



97 cc. 



V7\ 



F 1 £ 



Partially soaled [ I Fully sealed 



Figure I. Average Vent Losses of Liquid in Partially and Fully Sealed Glass Jars 

 Processed under Steam Pressure at 240° F. 



In all of the 144 tests, the fully sealed jars had smaller vent losses than the 

 corresponding partially sealed jars. The average loss of weight of 72 partially 

 sealed jars was 44.6 grams; whereas, for the same number of fully sealed jars, 

 the average loss was only 6.6 grams. The smaller loss of contents left the 

 liquid level much higher in the fully sealed jars than in the partially sealed 

 jars. This fact has a practical application in home canning, because loss of 

 jar liquid results in an actual food loss as well as an unattractive appearance. 



