536 MICROBIOLOGY OF -FOODS 



WATER SUPPLY. Another essential for the success of the canner is 

 an ample supply of pure water. It is a well-known bacteriological 

 fact that outbreaks of spoilage have occurred in canneries which could 

 be traced to organisms getting into the goods from the water supply. 



RECEPTACLES. The commercial canner recognizes two essentials for 

 suitable containers for his goods. First, they must be tight, both to 

 prevent the escape of the contained material and the entrance of con- 

 taminating organisms. Second, they must be of a material which will 

 withstand erosion or corrosion for a reasonable length of time, without 

 giving up any notable quantity of foreign material to the food with 

 which they may be in contact. Glass is most satisfactory from this 

 consideration, but for reasons previously stated it is impracticable for 

 use on a commercial scale. The difficulty from erosion in tin cans has 

 been largely overcome by the use of enamelled cans as mentioned above. 



DEGREE OF HEAT REQUIRED. * Factors in Processing. The heating 

 of food products after placing in the containers is termed processing 

 by the commercial canner, and he appreciates fully that upon the care 

 with which the processing is done depends the success of the entire pack. 



The several factors which enter into the successful processing 

 of foods, either in commercial or home canning may be enumerated as 

 follows : (a) length of time, (b) number and resistance of spores present 

 in the material, (c) size of container, (d) consistency of contents of the 

 container, (e) initial temperature, (/) agitation of the container during 

 processing. 



Length of Time Required. Fig. 152 gives the curves showing the 

 time necessary at various temperatures to destroy the spores of three of 

 the most resistant organisms found in canned foods when about fifty 

 thousand spores per c.c. are present. It will be noted that a drop of ten 

 degrees Centigrade necessitates about ten times as long for the destruc- 

 tion of the spores. For instance in organism No. 26 six minutes at 

 i25C. are necessary and about sixty-five minutes at 115. 



Number and Resistance of Spores. Fig. 1 53 shows the influence of 

 the number of spores on the processing time. It will be noted that 

 organism "C" when about twenty spores were present required twelve 

 minutes for their destruction; when about fifty thousand spores were 

 present, sixty minutes were necessary. In other words, at a tempera- 

 ture of n5C. nearly six times as long was found to be necessary 



* The author is indebted for charts and data to Dr. W. D. Bigelow, Chief Chemist of the 

 National Canners Association. 



