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.
Most vegetables and fruits in their normal condition are made up very largely of water. Many of them contain 80 to 90 per cent, of plain ordinary H20. A pumpkin is actually more fluid than milk - if its cell-structure were the same as that of milk it would be served at the table in a pitcher and poured out into glasses! Now these little bacteria which I have referred to - and will have to mention again many times in the following chapters - cannot increase and multiply unless their surroundings contain a certain amount of moisture.
Long ago our ancestors, when they still wore callouses instead of cordovans on their feet, and furs around their loins instead of around their necks, discovered that certain fruits put on hot stones in the sun or strung up on strings to dry, could be saved for winter. Of course they knew not the reason for this, but the fact was of very practical importance. Up until the days of our grandmothers, fruits generally and a few vegetables were "sun dried," or dried over the stove, or "evaporated," very generally.
Then canning came in, and as these dry products were hard to prepare and not wholly satisfactory, evaporating became almost a lost art in the home. In certain dry climates it continues to be used extensively in the preparations of certain fruits for market. But by the new methods vegetables and fruits of almost all kinds can be dried easily, quickly, and cleanly in the home with inexpensive apparatus. There is every indication that within the next few years dried vegetables will again be as common in every home as canned vegetables. By the new methods we take the moisture out with a continuous current of heated air, called the process of "dehydrating," which in plain English means "taking out the water"-and thus frustrate the diabolical purposes of the destructive bacteria which would otherwise claim our vegetables and fruits as their natural prey.