A major difference between sterilised foods (canned and bottled) and foods preserved by other methods, such as dehydration and freezing, is that sterilisation destroys the micro‐organisms that would otherwise destroy the food, whilst the other methods of preservation create an environment hostile to the micro‐organisms present in the food. In practice, this makes packaging of foods to be sterilised much more critical than packaging of foods preserved by other means. Leakage of small quantities of water into packages of dehydrated foods, for example, will shorten the storage life of the product but, unless gross leakage occurs, immediate deterioration will not occur. With a sterilised food, even the penetration of a single bacterium into a package can bring about the almost immediate demise of the food because the environment inside the package is usually ideal for microbiological growth. Fig. 1 shows the typical effect of leakage on sterilised and dehydrated foods. The perfect seal necessary for sterilised foods has, historically, been the main reason for the slow introduction of flexible pouches for sterilised foods, but modern technology now permits adequate seals to be made in suitable flexible materials and these are playing an increasingly important role.
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