2 BULLETIN 196, U. S. DEPARTMENT OF AGRICULTURE. 
The tomato is the most important vegetable processed at boiling temperature, which 
is usually maintained for 50 minutes. 
Cooking at a temperature above the boiling point is necessary or advantageous for 
most vegetables, fish, milk, and meats. It is accomplished in retorts where steam is 
admitted under pressure, in retorts where water can be superheated, or on the open 
calcium chlorid or oil bath. 
Among the vegetables requiring a high temperature in processing are corn, peas, 
beans, both green and dry, pumpkin, beets, and sweet potatoes. Corn is one of the 
difficult products to can, requiring a temperature of from 245° to 250° F. for from 75 to 
80 minutes, depending to a considerable extent upon how dry it is packed. If very 
dry, the heat will penetrate to the center of the can very slowly, the actual time 
required to raise the center to the temperature of the bath being from 55 to 65 min- 
utes. In a can of peas this is accomplished in 6 or 7 minutes, the difference being 
due to the fact that heat currents are set up in the liquid portion of the peas, while’ 
they are absentin the corn. The necessity for a high temperature is therefore depend- 
ent upon the ease with which the heat can penetrate the product, as well as the 
resistance of the organisms. Some products which were formerly processed by boil- 
ing for a long time are now given a higher temperature for a few minutes, as the prod- 
uct has a much better appearance when it is not overcooked. 
Meat products, as a rule, contain highly resistant organisms, besides which the 
majority of these foods are of such a consistency that the heat penetrates them very 
slowly. As a class they require the heaviest process. Milk also contains very 
resistant germs, but being liquid it heats rapidly; in order to keep it smooth and 
prevent the portion in contact with the tin from scorching, the cans are turned or 
agitated almost continuously during the cooking. 
DETERMINATION OF TEMPERATURE AND TIME OF PROCESSING. 
In sterilizing, the heat must be applied equally to all cans, and it is therefore neces- 
sary to deliver steam at the bottom of the kettle, whether open or in a retort, to insure 
a circulation of the heat. In retorts, whether steam or hot water is used, there must 
always be a vent open to give off steam in order to hold the heat uniform at all points. 
The thermometer is the all-important tester, for if it does not show the proper degree 
of temperature, spoilage will follow. To test the uniformity of temperature in a 
retort, self-registering thermometers are sealed in a number of cans when placed in 
the crates, the cans are marked, and when the cooking is completed the thermometers 
are examined and compared, so that the heat may be adjusted until all give like read- 
ings. Inasimilar manner the time required for the heat to reach the center of the can 
is obtained, experimental lots being run for varying periods, and the temperature 
noted. The calcium chlorid or oil bath acts in the same way as the open water bath. 
The writer employs two methods of determining the temperature in the center of 
a can and the rate of penetration. First, a thermometer is placed in a packing joint 
which is soldered into the can so that the bulb will just reach the center. By placing 
a collar an inch above the gasket the can may be submerged in oil and heat applied 
until a certain temperature is reached. The length of time necessary for the ther- 
mometer inside the can to reach the same point as that on the outside, or within from 
2 to 5 degrees of the outside, as experience demonstrates may be sufficient, must be 
allowed in the retort and the heating then continued for such an interval as may be 
found necessary for sterilization. For example, if the spores of certain organisms are 
killed at 230° F. in 12 minutes, and it should take 20 minutes to cause the content 
of the can to become heated, it would require 32 minutes as a minimum for process- 
ing, and as a margin of safety the recommendation would be for a longer time, 
probably for 40 minutes. 
The second method of determining temperature in different parts of the retort and 
in the center of cans is to seal a thermocouple in the can and connect it with a record- 
