CANNING 509 
Exhausting. The can is heated until hot in order to drive out as 
much air as possible. This is not done with produce which is canned 
hot or which receives a hot brine. 
Closing the Cans. This is now done mostly by machinery whether 
the cans are soldered or crimped. 
Processing. This is the final treatment given the cans and is done 
soon after the cans are capped. This may be done either below or 
above the boiling-point. The desired temperature is maintained either 
by hot water or an atmosphere of steam. After the ‘‘ process ”’ the 
cans must be cooled else the products will be over cooked. This is 
probably one of the most important steps in the canning procedure. 
Much loss is often caused by errors at this point. It is often necessary 
to make the ‘ process’ a subject of careful study because the length 
must often vary even from day to day during the packing of the same 
goods. 
Furthermore, it is known that the process is dependent upon the 
character of the contents of the cans. Acid products like strawberries 
require a lower process than a product like corn or beans. The thermal 
death point of microorganisms is lowered by the presence of acid. Bit- 
ting and Bitting (1917) have studied the heat penetration of cans and 
found a great variation with the character of the food. The tempera- 
ture of a No. 3 can filled with water raised from 85° F. to 210° F. in four 
minutes. Sweet potatoes gave different results and were decidedly 
more sluggish in their change of temperature. 
The Container. In commerce tin cans are almost exclusively used 
although paper cans have a promising outlook. Many shapes and 
varieties are now used. Bitting makes the following statement with 
regard to this: 
First, the cans were made to utilize a standard sheet of metal with the min- 
imum of waste by the method of can making in vogue at the time. This resulted 
in cans of arbitrary volume, bearing no definite relation to standards of volume, 
like the pint, quart or gallon and unfortunately they did not bear a close rela- 
tionship to the quantity that would be consumed at a single meal by an average 
family. A size of package was started, however, which has persisted because 
of a fixture in trade and the expense in changing machinery, cans, shipping 
cases, etc. Secondly, was the introduction of sizes to fit a given weight of a 
certain product. This has been particularly true of meat products, as 4, 8, 12, 
and 16-ounce cans. The sizes that will hold these weights of a ground meat 
will not hold the same quantity if cereal be added or if large cuts or pieces be 
used in place of the finely ground product. Thirdly, is the attempt to make 
cans that will hold a quantity of a given article to retail at a popular price, like 
