The effect of the various steps in the canning process was also investigated. In the "cooker" many bacteria are destroyed, the more resistant ones, however, remaining uninjured. Two-pound cans which were given a heating' at 120° C. (248° F.) for thirty minutes were found to contain living bacteria, and cans so treated frequently become much disturbed within a few days. On the other hand, if the heating process is continued for a sufficiently long time all bacteria are destroyed. The reason for the necessity of the long period of beating is the low conducting power for heat of the corn. Experiments made with maximum regis tering thermometers showed the time necessary for the temperature applied to record at the center of two-pound cans, as follows: water, starch and the like, variations of fifty to seventy-five minutes being found in different fac tories. Sweet corn undergoes fermentative changes even more rapidly than do peas, because of its high percentage of sugar, and especially from the fact that the kernels are broken, thus allowing direct This is strikingly confirmed in a practical way by the fact that souring, in many cases, is found only at the center of the cans, and in a majority of cases the fermentation probably begins at that point.
The use of mild antiseptics has also been of frequent occurrence in the packing of corn, the object being not only to prevent development of bacteria, but primarily to render the corn white in color. Excessive heating gives a slightly brownish coloration to the corn, which has been counteracted to some extent by the use of sodium sulfite and similar compounds. The use of antiseptics or bleachers of any kind is not free from objection, as, even if the amount is so small as to be uninju rious to health, the flavor of the article may be somewhat affected.
Tomatoes.—In the canning of tomatoes, the fruit is first scalded to make easier the removal of the skins. The peeled and properly prepared pulp is then put into the cans by means of a machine which may serve both as a preliminary heater and as a filler. The preliminary heating is of advantage as it saves time in the final heating or steriliza tion process. As with other vegetables, the cans are generally capped by use of a machine, when the canning operations are conducted on a large scale.
As tomatoes are more watery than corn, they may be more readily heated through and hence do not require so long a sterilization process. They are, however, extremely liable to fermentative changes if the heating is not thoroughly done.
Other kinds of vegetables are prepared in simi lar ways. It is essential to take into considera tion oniy the physical character of the food and the changes it undergoes on heating to modify the process to suit an individual case.
Fruit-packing.
The packing of fruits is in general accompanied by less danger of spoilage than with vegetables, owing to the presence of natural acids and to the greater water content and resulting higher con ductivity. As in the case of vegetables, specialized machinery has been devised for the carrying out of certain processes. A good example of this is in
the peach peelers and pitters. Small stone-fruits are packed whole, i. e., without removal of the pits. A syrup of cane-sugar and water is added to supply liquid.
The sterilization may be carried out in retorts, or an open water bath may be employed, in which case the temperature does not get above 100° C. (212° F.). The spoiling of fruits is of a different character from that found in vegetables, as in the former case the sugar is most frequently fermented to alcohol and carbon dioxid. Trouble from this source is relatively rare, however.
Extent of the canning industry.
The canning of fruits and vegetables has shown an interesting tendency toward centralization in those localities especially adapted for the growth of special kinds of materials. Baltimore, the most eminent canning center, is perhaps an exception to this, as here are packed annually enormous amounts of pineapples as well as other southern fruits.
New York state lead, in 1899, in canning corn, apples and pears, and also packs large amounts of beans and peas. A second corn-canning area is found in Maine, the only one of importance in New England, and a third of greater extent in the central states of Iowa, Illinois and Indiana.
Tomato-packing is perhaps the most widely dis tributed of these special branches of the industry, and in this line Maryland stands in first place, fol lowed by New Jersey, and then by Indiana, California and Delaware. The tomato may perhaps be regarded as the most typical canned fruit. In 1906, there were 9,074,965 cases of this fruit packed, aggregat ing over 200,000,000 cans of three pounds each.
The industry, as has been said, is one which has had a rapid growth in this country, and with care and strict adherence to making quality a first con sideration, is bound to increase to still greater pro portions. This fact is made evident by a study of the Census figures showing the increase from 1889 to 1899 in the five leading canning states for tomatoes and corn. The figures refer to the num ber of cases of twenty-four cans each : In 1899, fourteen states packed 94.6 per cent of the tomatoes and 92.3 per cent of the corn for the United States. Maryland alone packed 31.4 per cent of the total pack of tomatoes, and Maryland, New Jersey and Indiana, 53.4 per cent. New York alone produced 21.1 per cent of the total can of corn, while New York, Illinois, Iowa, Maryland and Maine produced 78.3 per cent.
For further detailed statistics the reader is referred to the reports of the Bureau of the Census.
For Canada, in 1891, there were sixty establish ments engaged in fruit and vegetable canning, with a total capital of $571,520, employing 2,304 per sons, paying $523,151 for materials, and turning out a product valued at $929,778. In 1901, there were fifty-eight establishments, with a total capital of $2,004,915, employing 4,640 persons, paying $1,571,681 for materials, and turning out a product valued at $2,831,742.