Important: Safety Warning
This page describes home-canning methods from before the causes of botulism were understood. Canning low-acid foods without a pressure canner, as described here, can allow the growth of Clostridium botulinum, whose toxin is among the deadliest known. Follow current USDA home-canning guidelines instead.
This information has been left in for historical purposes but should not be acted upon.
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Canned Foods
In canning food, we depend upon heat to free the article of all organisms; the food itself and everything with which it comes in contact must be sterilized by heat; then this sterile food must be sealed to exclude all organisms from without.
Fruit put up in a heavy syrup, as we noted above, need not be sealed so carefully; the same is true of foods put up in vinegar, and some articles acid in themselves, as rhubarb, cranberries, and lemons, may be sealed in cold water, without the application of any heat.
This is because bacteria and yeasts do not attack acid substances.