This section is from the book "Save It For Winter.", by Frederick Fry Rockwell. Also available from Amazon: Save It For Winter; Modern Methods Of Canning, Dehydrating, Preserving And Storing Vegetables And Fruit For Winter Use, With Comments On The Best ... For Saving, And When And How To Grow Them.
While there are, in general, two methods of canning in use-the hot-pack and the cold-pack-the latter is so much better adapted under almost all conditions for home use, that for all practical purposes it may be said to have replaced the other. Some products, such as soups and "rations," are, because of their physical make-up, packed while hot, but this is only a matter of convenience.
Under the old or hot-pack method, the product to be preserved was heated until sterilized and then placed while hot in jars or cans and immediately sealed. By the new method, the materials are packed cold in the jars, covered with the syrup or liquor which is to go with them, heated until sterilized and immediately sealed. The advantage of the cold-pack method is, of course, obvious, in so far as convenience and quickness are con cerned. In addition to that, however, better results are obtained. Packing the products before sterilization instead of after, very greatly reduces the possibility of having the product re-infected with the bacteria or mold from the air, fingers, or other sources.
With the cold-pack method, either the one "period" or the intermittent or fractional process of sterilization may be used. In the former the product is put in and left until thoroughly sterilized at one heating, when it is sealed and finished. By the latter, which has already been mentioned, the product is heated two or three times, at intervals of twelve to twenty-four hours. The advantage of this is that the product may be thoroughly sterilized without using the high temperature necessary by the one-period method. If the sterilizing can be done when the fire in the home is being used for other things, on successive days, it may mean that but little extra work will be required. Ordinarily, however, the one-period method is the one most convenient and, therefore, most widely used.