METHODS AND PROCESSES. 23 



wards closed, all in one series of operations, without touching by 

 hand. As tlu> cans pass from the capping machine they may be 

 submerged in a bath of boiling water to test for leaks. Any imper- 

 fection in the can or defect in sealing will be shown by a series of 

 air bubbles issuing from the opening, and the can is at once taken out 

 by the inspector for repairs. 



PROCESSING AND COOLING. 



After capping, the cans are processed according to the nature of 

 the contents. The cans are collected in large iron baskets, which 

 usually hold 270 No. 2 or 180 No. 3 cans, and three baskets fill a re- 

 tort. If the processing is conducted at boiling temperature, the 

 retort is not closed, but steam is turned into the water which covers 

 the cans. If the temperature is to be above the boiling point, the 

 retort is closed and either the steam is turned into the retort until 

 the proper pressure and temperature has been reached, or water is 

 first turned in to cover the cans and the steam is admitted until the 

 temperature has been attained. In processing fruits it is customary 

 to use long vats containing boiling water and equipped with auto- 

 matic conveyers, which carry the cans or crates through at such a 

 speed as will process them for the necessary length of time. This 

 period varies with the product. Sterilization depends on adminis- 

 tering the proper amount of heat, and heating above the required 

 temperature or for longer than is necessary only cooks the material 

 to no purpose. 



As soon as the processing is completed, the cans should be cooled 

 with water. Unless this is done, the heat will be held so long that 

 the contents become overcooked fruits are softened, and tomatoes 

 become liquid, even blacken, peas' break and make muddy liquor, 

 while corn acquires a brown color and a scorched taste. The cooling 

 may be done by turning cold water into the retort, by removing the 

 basket of cans to a cooling tank, or by spraying with water in the 

 air. There is less difference in the results obtained by different 

 methods of applying either heat or cold than some claim; the im- 

 portant point is to accomplish these steps quickly. 



In canning operations the product, salt, sugar, or other seasoning, 

 and water are the only materials used. No hardener, bleach, or pre- 

 servative is employed, and in commercial canning there never was 

 as much preservative used as is common in the household operation. 

 Saccharin and sulphites were formerly used in corn and peas, but 

 their use has now been practically discontinued ; on the other hand 

 the practice of selling a "canning compound" to housewives still 

 continues, and will only cease when the nature and effects of such 

 chemical preservatives are known, and the lack of necessity for their 

 use is appreciated. 



