22 MASS. EXPERIMENT STATION BULLETIN 426 



penetration and thermal death time. Although much is yet unknown regarding 

 all factors which govern process times, much progress has been made in this field, 

 largely through the efforts of the National Canners Association and the labora- 

 tories of several of the can manufacturers. 



In view of the importance of home canning it is surprising that there has been 

 but little effort to make a scientific study of the adequacy of home-canning process 

 times. Cover, Turk and Kerns (1943) have applied some of the more recent 

 technical methods of the study of process times for home-canned meats. They 

 observed that the slow air cooling of glass containers in home canning allowed 

 further sterilization to take place and pointed out that the method they used in 

 calculating process times did not take this into consideration. 



A research program designed to make a scientific study of home-canning process 

 times was initiated by the Food Technology Department of the Massachusetts 

 State College about two years ago. In this investigation methods developed 

 by the National Canners Association Research Laboratory and associated labora- 

 tories are being applied to the determination and evaluation of home-canning 

 process times. More recently a similar investigation has been started by the 

 Bureau of Human Nutrition and Home Economics of the United States Depart- 

 ment of agriculture. 



Tischer and Esselen (1945) have summarized a preliminary investigation as 

 follows: 



To obtain information on causes of spoilage in home-canned foods 293 

 jars of spoiled and sound home-canned foods put up in 1942 in Massachu- 

 setts by 270 families were collected. These families canned a total of 

 67,632 jars and reported an over-all spoilage of L96 percent. Approxi- 

 mately half of the jars received were spoiled and the remainder were con- 

 sidered to be sound. Each jar was examined bacteriologically and for 

 physical defects. Of 133 spoiled jars 101 appeared to have been under- 

 sterilized, 22 had been improperly sealed and 7 were apparently all right. 

 Out of 146 "sound" jars 51 contained viable organisms which might cause 

 spoilage under certain conditions. Four jars of tomatoes showed evidence 

 of putrefactive spoilage, caused apparently by a preliminary growth of 

 mold which created a favorable environment for the growth of a putre- 

 factive anaerobe present in the product. 



Of 19 putrefactive anaerobes isolated from spoiled jars the spores of 

 four, isolated respectiveh^ from asparagus, lima beans, and snap beans, 

 survived heating for 30 minutes at 230°F. (110 C). In phosphate buffer 

 their "F" and "z" values were but slightly below those of Cameron's 

 putrefactive anaerobe No. 3679. These organisms had a survival time of 

 from 320 to 820 minutes at 212°F. (100°C.). 



As represented by this investigation it would appear that 80-85 percent 

 of home canning spoilage is due to underprocessing and 15-20 percent to 

 faulty sealing. The boiling water bath method of processing is not ade- 

 quate to destroy certain types of bacteria encountered in home canning. 

 While a pressure canner correctly used is satisfactory for processing, 

 understerilization may result if it is mis-used. 



In studies on the determination of process times for home-canned foods, Esselen 

 and Tischer (1945) reported that theoretical process times for home-canned 

 asparagus, beets, carrots, corn, snap beans, spinach, and squash were determined 

 according to accepted methods, at processing temperatures of 212°F. (100°C.), 

 240°F. (116°C.), and 250°F. (121°C.). Process times based on the heat resistance 

 of Cameron's putrefactive anaerobe No. 3679 were compared with those based 

 on four heat-resistant putrefactive anaerobes isolated from home-canned foods. 



