DIFFICULTIES OF CANNING 193 



impossibility to can green com, and the preservation of peas 

 and beans has proved to be even more difficult. These 

 products are successfully preserved to-day, but until home 

 canning was stimulated by the war-time food shortage they 

 were rarely canned except in factories, for they are far 

 more difficult to preserve in this way than foods containing 

 considerable amounts of sugar or acid. The problem of 

 canning any product, whether it be fruit, tomatoes, corn, or 

 peas, is simply that of totally destroy- 

 ing the microorganisms present that 

 are capable of growing in that par- 

 ticular food. If the material, like 

 most fruits, contains so much sugar 

 or acid that only yeasts or molds are 

 able to grow in it, preserving is quite 

 easy, because simple boiling kills Fig. 63. Spore-producing 

 these organisms. Corn, peas, and bacteria found in canned 

 beans, however, not only furnish a 



favorable environment for the growth of bacteria, but also 

 are sure to contain bacteria which develop spores (Fig. 63) 

 and can therefore resist considerable boiling. If two or three 

 or even one of these highly resisting spores survives, the 

 canning may prove quite ineffectual. Tomatoes contain con- 

 siderable acid but little sugar, and therefore stand midway 

 between these two groups of foods. Ordinary boiling is 

 generally sufficient to preserve them, especially if sugar be 

 added, but they are more likely to spoil than are fruits. 



The remedy in all such cases is higher or longer heating, 

 since no satisfactory means of destroying bacteria is known 

 except the application of heat. Even spores may be destroyed 

 if the proper method is adopted. 



