18 MASS. EXPERIMENT STATION BULLETIN 426 



have all the requirements for promoting good growth except that their acidity is 

 on the border line. For this reason toxin production in cans of asparagus, string 

 beans, beets, pumpkin, and spinach may occur irregularly. The acidity of certain 

 canned vegetables was found to be greatly affected by the quality of the material 

 put in the cans. Experiments with spinach showed that a small amount of 

 'rotted material would reduce the acidity to a point where CI. hotidinum could 

 grow and develop a toxin. These results were in essential agreement with those 

 reported earlier by Schoenholz, Esty and Meyer (1923). These latter authors 

 also pointed out that the use of fresh and sound raw products, preferably ob- 

 tained directly from the home garden and packed with the least delay, is one of 

 the greatest means of protection against botulism. 



As has been emphasized by many authors it is important to realize that fre- 

 quently sufficient toxin to cause illness or death may be produced in canned foods 

 before the appearance of the container or the appearance and odor of the food it- 

 self would give any warning of its dangerous nature. 



Acidity 



It is well known that acidity inhibits the growth and toxin production of 

 CI. botulinum. Attempts have been made to acidify low-acid foods so that they 

 could be safely processed in a boiling water bath. Cruess (1932) believed that 

 vegetables could be safely processed at 212°F. (100°C.) if the initial brine was so 

 acidified that it would be at a pH of 4.5 or less after processing. Nehring and 

 Bothe (1936) reported that it was wholly impractical, through the addition of 

 acid to a vegetable conserve, to reduce the heat treatment. Savage and Hauwicke 

 (1923) observed that the spores of CI. botulinum were not likely to be killed by 

 temperatures used in canning fruit, but if present would probably remain as such 

 and not multiply. 



In a study of the relationship of incubation temperature to viability, rate of 

 growth, and toxin production of CI. botulinum in different vegetables, Starin 

 (1926) found that peas and corn showed decomposition. String beans and spinach 

 exhibited little or no change in appearance or odor and the amount of toxin found 

 was less than in the other two. This was thought to be due to the relatively high 

 acidity of the string beans and spinach as compared with other so-called non- 

 acid foods. 



While acidification is used commercially, under carefully controlled conditions, 

 to shorten the process time for certain low-acid foods, it is not a procedure to be 

 generally recommended for home canning. In many cases, if sufficient acid were 

 added to do the job intended, it would impart an off-flavor to the product. It is 

 also difficult to control conditions in the home. For example, if vinegar were 

 used as an acidulent, the directions would probably be based on ordinary 40 

 grain commercial vinegar. However, many homemade vinegars are less acid 

 than this and their use w^ould very likely lead to trouble. 



Fong (1926) reported that vegetable brine must have a pH value below 5.0 to 

 decrease the death time of bacteria at 212°F. (100°C.). A final pH value of 5.0 

 or greater produced no abnormal acid taste. Blanching with acid was effective 

 in the destruction of bacteria during subsequent processing. When vegetables 

 were processed for not less than one hour at 212^F. (100°C.), a safe pH value of 

 the original brine for the prevention of spoilage by CI. sporogenes and the thermo- 

 philes was about 3.0. CI. botulinum required a pH value of 2.8. 



