HEAT IN THE PRESERVATION OF FOOD PRODUCTS 465 



quire a very high temperature to destroy the bacterial spores sure to be present. 

 Briefly, the methods employed in canning some foods follow: 



Meat. — In the meat-canning industry, lean meat is largely selected for two reasons. 

 Fat, well-finished carcasses bring a better price when offered for sale in the fresh con- 

 dition; and in the second place, lean meat has a better appearance in the canned 

 state than fat meat. The selected meat is cut into pieces of approximately from 

 I to 4 pounds in weight, according to the size of the tins in which it is to be preserved. 

 The pieces are cut as nearly as practicable the same size, not only for purposes of 

 appearance in the cans when opened, but also that the process of sterilization may 

 be more uniformly carried out. If the pieces were of different sizes, the smaller 

 ones would become thoroughly cooked and disintegrated before the larger ones were 

 sterilized. 



After the pieces have been selected and dressed they are parboiled before being 

 placed in the containers, the time ranging from eight to twenty minutes, according to 

 the size of the pieces of meat. The object of parboiling is to secure the shrinkage 

 which always takes place on heating. Meats put into tins in the fresh state and 

 sterilized shrink to about two-thirds of their original volume. When the meat is 

 put directly into boiling water, there is less loss of protein than when the meat is 

 placed in cold water and heated gradually. During parboiling, the meat loses 

 about I per cent of the protein content, about one-third of the total meat bases, 

 and so per cent of the mineral matter. 



This shrinkage by parboiling tends to make a more concentrated article, thus 

 favoring transportation, and, pound for pound, the nutritive value is not lowered. 

 Practically, the nutritive value of a pound of properly canned beef is about one-third 

 greater than that of i pound of fresh beef of the same kind. After parboiling, the 

 meat is placed in tins, by hand or by machinery, and to each can is added a small 

 quantity of "soup liquor," the maimer of preparation of which is not disclosed by the 

 packers. It may be regarded as a thin soup, the object of which is to fill up the 

 spaces between the meat, and to add condimental substance to render the meat more 

 palatable. 



After the cans are fiUed, they are closed and processed in suitable retorts by steam 

 under pressure, as previously described, the temperature ranging from 110° to 120°. 



A modification of the usual method consists in exhausting the cans in vacuo, and 

 automatically sealing them in the exhausted state, thus removing all the air and other 

 gases, after which they are placed, on an endless conveyor and dipped into an oil 

 bath at a temperature of 115°, the speed of the Conveyor being so regulated that 

 the cans remain in the bath a sufficient length of time to complete sterilization 

 before they are carried out at the opposite end. They are next carried automatically 

 into a solution of carbonate of soda, and finally into pure water, after which they 

 are dried; painted with a shellac or lacquer and labelled. 



Fresh meats other than beef or pork are canned in a fresh state. When game 

 and wild fowl, as well as domesticated chickens, ducks, geese, turkeys, and pigeons are 

 used, the general process is as already described. Horse meat is used more or less 

 commonly in some European countries, but probably rarely in the United States. 



Fish. — ^The process of fish canning does not differ materially from that of other 



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