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.
There is one thing more which should be fully realized about these Vegetable microorganisms which we have been considering, before we can plan intelligently just how to get the best of them. Notwithstanding their minute size and the incredible rapidity with which they increase, each individual germ has to go through its complete life cycle, just as a plant does or a tree; each is a living organism. Each individual germ, no matter how many millions of them there may be in a single spoonful of vegetables or fruit, must sprout from a seed or "spore," grow, mature, and in its turn reproduce seed or spores from which the next generation springs. It is absolutely impossible for any form of bacteria, yeast, or mold to develop spontaneously in any vegetable product.
On the other hand, to make any vegetable product safe from their attacks it is necessary to destroy not only the growing organisms, but all the seed or spores, as well. Any one knows from common observation that Nature insures the continued existence of the various forms of plant life by protecting the germ in the seed-which carries the thread of life from one germination to the next- against conditions which would destroy the growing plant. You have seen come up in your garden in the spring, plants from seeds of such tender things as melons and squash, which have remained uninjured in the ground over winter. In like manner the seeds or spores of bacteria, molds and yeast are much more difficult to destroy than the growing organisms themselves. Therefore, to make safe the products which we would keep for winter, it is necessary to be certain that the treatment given is sufficient to destroy the former as well as the latter.
As I have already stated, food products may be saved either by killing the germs present and making it impossible for others to get at the food, or by making the environment so unfavorable for the particular form of germ life to be dealt with that it could not develop sufficiently to cause any trouble. In canning of all kinds, the former method is utilized, the germs are destroyed by heat - or in more scientific terms, the product is "sterilized." In some instances this sterilization is also supplemented by a second method, i.e., by the use of "preservatives" which make conditions unfavorable for any further development of bacteria or yeast or mold.