This section is from the book "Home Canning Recipes And Instructions", by Butler Mfg. Co. See also: Ball Complete Book of Home Preserving.
This process of killing the bacteria and spores of vegetables and meats may be very successfully accomplished in the BUTLER HOME CANNER in two ways:
1. By intermittent heating, which means boiling the filled jars or cans a short time for each of three successive days, thereby allowing the spores to become active between days so that the second or third boiling will easily kill them.
2. By one day or Long Boiling Process which means boiling the filled jars for a longer period (3-4 hours) or one day only. Although the intermittent method involves more trouble than the one-day process, it is safer in the long run, especially after a dry season, which increases the probabilities of spore-forms.
If the reasons for the spoiling of canned fruits and vegetables are borne in mind, and a generous supply of common sense is used in following the directions for canning, there is small chance for a loss of food from spoiling and the summer crop is conserved.
 
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