Introduction
Many food plants were built at a time when the hygienic quality of the food
processing environment itself was less important than it is now. The focus was
on making the food safe by using the right preservation technique to kill the
microorganisms present in or on the food or to prevent their multiplication.
Killing was achieved by giving the product a severe heat treatment. Multi-
plication was prevented by acidification (sometimes by microbial fermentation)
and/or the addition of salt or sugar, sometimes in combination with the addition
of chemical preservatives. The adverse influence of preservation treatments on
the nutritional and sensory quality of food products, and their possible adverse
toxicological effects, were either accepted and regarded as unavoidable, or
simply not understood.
In more recent decades and in an increasing number of countries, consumers
have become more demanding, initially with respect to taste and colour, and
more recently with respect to the nutritional value of the products they choose.
They have also become more concerned about the use of synthetic preservatives
and other chemicals in food. Manufacturers, often with the help of research
institutes and universities, have responded by attempting to improve traditional
preservation treatments and by developing other ways of preservation. Reducing
the severity of heat treatments has been quite successful with the introduction of
improved retorts, where heat transfer is dramatically improved by movement of
the containers during the heating and cooling stages of the process, and where
improving the design of tubular heat-exchangers led to significant improvements
in heat transfer. For liquid products, the introduction of plate heat exchangers
resulted in some products that, pasteurised, could hardly be distinguished from