Thermal Food Processing

370 Thermal Food Processing: New Technologies and Quality Issues
FIGURE 12.2 Reel-and-spiral cooker-cooler for processing cylindrical food cans. (Courtesy
of FMC Foodtech. With permission.)
of food retorting is to heat a food in a hermetically sealed container so that it
is commercially sterile at ambient temperatures (see Section 12.3). In other
words, so that no microbial growth can occur in the food under normal storage
conditions at ambient temperature until the package is opened. 5 Once the package
is opened, the effects of retorting are lost, the food will need to be regarded as
perishable, and its shelf life will depend on the nature of the food itself. Various
packaging materials are suitable for use with retorted foods, which includes not
only tin plate, but glass, plastic pots, trays, bottles and pouches, and aluminum
cans.
The most heat resistant pathogen that might survive the retorting process of
low-acid ready meals is C. botulinum. This bacterium can form heat-resistant
spores under adverse conditions, which will germinate in the absence of oxygen
and produce a highly potent toxin that causes a lethal condition known as botulism.
This can cause death within 7 days. In practical terms, the sterilization
process must reduce the probability of a single C. botulinum spore surviving in
a pack of low-acid product to 1 in 1 million million (i.e., 1 in 10 12 ). This is called