VACUUM-PRESSURE IN GLASS CANNING JARS 19 



Products canned most frequently 



Number of jars 



Tomatoes and tomato products 5,565 



Beans — shell, lima, string 2,584 



Peaches 1,924 



Beets 786 



Corn 720 



11,579 or 70 percent of 

 the jars packed 



SUMMARY 



1. Fully sealing all-glass jars prior to heat processing seems to answer the 

 problems of reducing losses of liquid and improving general appearance of the 

 product. 



2. Fully sealing the jars, releasing pressure slowly, and leaving a large head- 

 space decreased loss of liquid in pressure-processed jars. 



3. An apparatus for the determination of pressures developed in all-glass 

 jars during processing is described. The principal feature of this apparatus 

 is an aluminum cover duplicating the glass cover. 



4. In water-bath processing, the pressure developed in partially sealed jars 

 was negligible. Fully sealed jars developed from 2 to 6 pounds pressure. Glass 

 jars are strong enough to withstand this pressure without bursting. 



5. In pressure processing, the pressures developed in partially and in fully 

 sealed jars were similar, being within one pound of the retort pressure. The 

 fully sealed jar took longer than the partially sealed jar to attain this pressure. 

 Usually the rise in pressure of partially sealed jars corresponded to the rise in 

 pressure in the retort. 



6. There was practically no difference in the penetration of heat into jars 

 of water either partially or fully sealed. 



7. Two methods of determining vacuums in glass jars of food were com- 

 pared. The vacuum desiccator method was perfected and gave accurate and 

 consistent readings of partial vacuums in freshly sealed glass jars. The water 

 displacement method was found to be reliable and checked with the former 

 method. 



8. The vacuums present in sealed glass jars were high, averaging well over 

 20 inches of mercury. 



9. Temperature of filling, volume of headspace, and condition of seal before 

 processing had no effect on the amount of vacuum formed in the jars after 

 processing. 



10. A practical survey of the use of the fully sealed method by 64 home 

 canners who used a total of more than 16,500 jars to pack 50 different products, 

 proved the practicability of this method in canning with all-glass jars. Of the 

 jars packed, 85.5 percent had no noticeable loss of liquid. Tomatoes, beans, 

 peaches, beets, and corn constituted the bulk of the products canned. 



