Quick Answers
Is it alright to let jars cool in the water they were processed in?
It is very important to remove jars from a boiling-water
canner immediately when the processing time is up. The
spores of certain thermophilic, or heat-loving bacteria,
such as those that cause flat sour spoilage, can survive
boiling-water processing. Because these bacteria thrive
at high temperatures, they can multiply and cause
spoilage if canning jars are left in the hot water to
slowly cool. Removing jars immediately for cooling at
room temperature will prevent this type of spoilage.
When processing low acid foods in a steam pressure
canner, the canner is removed from the heat source when
the time is up. Jars are left in the steam pressure
canner until the pressure returns to zero naturally.
This period of time, after removal from heat until the
pressure reaches zero, is considered part of the
processing time and is necessary for destruction of
microorganisms. Do not rush this cooling by placing the
canner under water, or by using a fan. The jars should
be removed immediately, following manufacturer's
directions, when the pressure returns to zero, and
cooled at room temperature.
Also, the cooling process helps pull the vacuum and therefore affects the seal.
Barbara Willenberg, Nutritional Sciences, University of Missouri-Columbia
Last update: Tuesday, May 05, 2009
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