Abstract
We processed applesauce, tomato juice, and cranberries in pint jars in a boiling water canner to test thermal processing theories against home canning of high-acid foods. For each product, thermocouples were placed at various heights in the jar. Values for fh (heating), fcl (cooling), and F82.2°C (lethality) were determined for each thermocouple location, and did not depend substantially on thermocouple location in accordance with heat transfer theory. There was a cold spot in the jar, but the cold spot during heating became the hot spot during cooling. During heating, the geometric center was the last to heat, and remained coldest the longest, but during coooling, it was also the last to cool, and remained hottest the longest. The net effect was that calculated lethality in home canning was not affected by thermocouple location. Most of the lethality during home canning occurred during air cooling, making cooling of home canned foods of great importance. Calculated lethality was far greater than the required 5-log reduction of spores in tomato juice and vegetative cells in cranberries, suggesting a wide margin of safety for approved home-canning processes for high-acid foods.
Highlights
Evidence indicates a revival of interest in home canning (Moskin 2009; Dickerson 2010)
The primary public health concern associated with lowacid canned food is the formation of botulinal toxin in the container (Weddig 2007); with acid or acidified canned foods the threat to public health is from Escherichia coli O157:H7 (Breidt et al 2010) or Listeria monocytogenes (Breidt et al 2014)
Temperature versus time was plotted versus thermocouple location for home canning of applesauce, tomato juice, and cranberries in heavy syrup processed in a boiling water canner (BWC)
Summary
Evidence indicates a revival of interest in home canning (Moskin 2009; Dickerson 2010). In order to establish safe home-canning methods, it is necessary to verify that processes deliver sufficient thermal lethality. Thermal processing operations in the canning industry aim to ensure adequate destruction of expected spoilage organisms and pathogens in the product based on reliable microbial thermal-death-time information. The design of adequate thermal processes requires an understanding of how a product heats and cools under processing conditions. Bee and Park (1978) noted that the design of heat processes is based on the measurement of temperatures in the coldest portion of the container at various time intervals. Weddig (2007) stated that the slowest heating region, or cold spot, of the container depends on product type, container type and size, processing method, and the heat transfer mechanism.
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