BOTULISM AND HOME CANNING 21 



potential sources of botulinum toxin. The process times recommended for such 

 products are not severe enough to destroy the spores of CI. botulinum if they are 

 present because the acidity of the product is relied upon to prevent the growth 

 of this organism. 



HEAT RESISTANCE OF CLOSTRIDIUM BOTULINUM 



Much work has been reported regarding the heat resistance of CI. botulinum, 

 particularly as it applies to commercial and home-canned foods. As a result of 

 this work it has been definitely established that it is necessary to use a pressure 

 canner, with processing temperatures of from 240°-250°F. (116°-121°C.) for 

 processing home-canned low-acid foods in order to destroy the spores of this 

 organism, as well as many other heat-resistant spoilage bacteria which may be 

 present. 



Esty and Meyer (1922) made a comprehensive study of the heat resistance of 

 the spores of CI. botulinum and their findings are still used as a basis for determin- 

 ing safe process times. They found that the maximum heat resistance of the 

 spores of this organism, artificially produced under the most favorable conditions 

 for growth and heated in a phosphate solution at pH 7.0, was as follows: 



4 minutes at 248°F. (120°C.) 



10 minutes at 239°F. (115°C.) 



32 minutes at 230°F. (110°C.) 

 100 minutes at 221°F. (105°C.) 

 330 minutes at 212°F. (lOOX.) 



They pointed out that the heat resistance of spores of the same strain may vary 

 considerably, depending upon several factors, some of which are unknown. The 

 average resistance of the spores, as found in approximately 20 grams of either 

 naturally or artificially contaminated soil, was less than three hours at 212°F. 

 The heat resistance increased as the concentration of spores increased; that is, a 

 longer process time would be required for a heavily contaminated product. The 

 heat resistance of the spores in the juices of 17 varieties of canned food varied 

 from less than 10 minutes, to 230 minutes at 212°F. (100°C.). 



In more recent studies to determine safe processes for canned foods, Townsend, 

 Esty, and Baselt (1938) found that the heat resistance characteristics of CI. 

 botulinum in canned foods differed from those in neutral phosphate. The work 

 of Esty and Meyer (1922) on this organism in neutral phosphate broth was well 

 substantiated. 



It is obvious from a study of available data that a boiling water bath process 

 time long enough to destroy the spores of resistant strains of CI. botulinum in a 

 product would range from six to twelve hours and would be impractical. For 

 this reason any one recommending boiling water bath process times should give 

 consideration to the fact that such times as are recommended at present cannot 

 be relied upon to destroy this organism. 



ARE HOME CANNING PROCESS TIMES AS RECOMMENDED 

 AT PRESENT ADEQUATE? 



For some years the process times used in the canning industry have been based 

 upon scientific determinations made through an application of studies' of heat 



