CHAPTER 11
Controlling the Microbiological Quality
of Foods
In Chapter 10 we surveyed the different methods used in the microbio-
logical examination of food and how these give us information about the
size and composition of a food’s microflora. We will now go on to
describe how data obtained from such tests can be used to make
decisions on microbiological quality and how accurate these judgements
are likely to be. It will become apparent that reliance on this approach
alone is an ineffective means of controlling quality so, finally, we will
examine how best to ensure the production of consistently good micro-
biological quality products.
11.1 QUALITY AND CRITERIA
We all feel we know what is meant by quality and the difference between
good quality and poor quality. One dictionary defines quality as the
‘degree of excellence’ possessed by a product, that is to say how good it is
at serving its purpose. In terms of the microbiology of foods, quality
comprises three aspects:
(1)Safety. A food must not contain levels of a pathogen or its toxin
likely to cause illness when the food is consumed.
(2)Acceptability/shelf-life. A food must not contain levels of micro-
organisms sufficient to render it organoleptically spoiled in an
unacceptably short time.
(3)Consistency. A food must be of consistent quality both with
respect to safety and to shelf-life. The consumer will not accept
products which display large batch-to-batch variations in shelf-
life and is certainly not prepared to play Russian roulette with
illness every time he or she eats a particular product.