CHAPTER 4
The Microbiology of Food Preservation
In Chapter 3 we outlined the physical and chemical factors that influence
microbial growth and survival in foods. We have also seen how knowl-
edge of these helps us to form a qualitative picture of a food’s microflora
and how mathematical models can be formulated which give a quanti-
tative description of microbial growth under differing conditions.
Manipulation of the factors affecting microbial behaviour is the basis
of food preservation (Table 4.1). In this chapter we will survey the
principal techniques of food preservation, with the notable exception of
fermentation which is discussed separately in Chapter 9. Since our main
concern here is the effect of preservation treatments on micro-organisms,
technological features will only occasionally be touched on. For more
detail on these aspects, readers are referred to more specialized texts on
food technology.
4.1 HEAT PROCESSING
4.1.1 Pasteurization and Appertization
Foods are subject to thermal processes in a number of different contexts
(Table 4.2). Often, their main objective is not destruction of micro-
organisms in the product, although this is an inevitable and frequently
useful side effect.
Credit for discovering the value of heat as a preservative agent goes to
the French chef, distiller and confectioner, Nicolas Appert. In 1795 the
French Directory offered a prize of 12 000 francs to anyone who could
develop a new method of preserving food. Appert won this prize in 1810
after he had experimented for a number of years to develop a technique
based on packing foods in glass bottles, sealing them, and then heating
them in boiling water. He described his technique in detail in 1811 in a
book called the ‘... Art of Conserving all kinds of Animal and Vege-
table Matter for several Years’. A similar technique was used by the