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