BOTULISM AND HOME CANNING 



23 



The theoretical process times for vegetables processed in a pressure canner at 

 240°F. (116°C.) were found to be somewhat shorter than those recommended at 

 present. Process times at 212°F. (100°C.) in a boiling water bath ranged from 

 5J^ to 12 hours and serve to show that such process times as are recommended 

 at present are inadequate to destroy certain types of bacteria encountered in 

 home canning. 



When the pressure canner is used, the relatively long come-up time plus the 

 slow air-cooling period contribute significantly to the sterilizing value of the 

 process. Eighteen to 35 percent of the sterilization occurs during cooling. In 

 the case of the boiling water bath, 90-98 percent of the lethal value of the process 

 must occur during the actual processing as the effect of the come-up and cooling 

 periods is comparatively small. 



The information obtained indicates that home-canning process times recom- 

 mended at present may be more severe than are necessary and in many cases 

 might be reduced. However, before any general recommendations are made, 

 more experimental work must be done on home-canning process times and careful 

 consideration given to the many variables encountered. Particular stress should 

 be placed on the correct operation and maintenance of pressure canners in order 

 to obtain the maximum sterilizing value from a given process. 



Preliminary process times as determined by experimental methods for certain 

 vegetables in pint jars are presented in Table 4. 



Table 4. Experimental Process Times as Determined For Home Canned 

 Vegetable in Pint Jars. 



Required Process Time 



Vegetable at 212°F. at 240°F. 



(100°C.) (lld^C.) 



Hours Minutes 



Asparagus .— 10 25 



Snap beans 10 22 



Beets (sliced) 6}i 30 



Carrots (sliced)-.. ■ 7^ 25 



Corn (whole kernel) 12J^ 45 



Peas.... 12 30 



Spinach \0\i 65 



Squash over 6 75 



U.S.D.A. Process Time 



at 240°F. (116°C) 

 Recommended in 1943 



Minutes 

 35 

 30 

 40 

 40 

 65 

 45 

 95 

 85 



The boiling water bath process times reported above are of equivalent steriliz- 

 ing value to the process at 240°F. (116°C.), and are based on the time necessary 

 to destroy the spores of CI. botulinum and certain other heat-resistant spoilage 

 organisms occasionally encountered in home canning. On the basis of these data 

 it would appear that boiling water bath process times as recommended at present 

 are inadequate to destroy the spores of all bacteria that are encountered in home 

 canning and that might occasionally give trouble. 



The experimental process times as listed above are not to be recommended at present 

 because (1) they must be checked further and (2) present methods of operating pressure 

 canners leave much to be desired in many cases and a safety factor, as yet unde- 

 termined, must be added to those process times. 



