CHAPTER 9
Fermented and Microbial Foods
9.1 INTRODUCTION
So far in this book we have been almost exclusively concerned with the
negative roles that micro-organisms play in food. There is however a
huge diversity of foods where microbial activity is an essential feature of
their production. Some are listed in Table 9.1 and in this chapter we will
describe a few of these in more detail and discuss some general features
of food fermentation.
Almost without exception, fermented foods were discovered before
mankind had any knowledge of micro-organisms other than as witness
to the effects of their activity. It was simply an empirical observation that
certain ways of storing food effected desirable changes in its character-
istics (Table 9.2). Originally the most important of these changes must
have been an improvement in the shelf-life and safety of a product,
although these became less important in the industrialized world with the
advent of alternative preservation methods such as canning, chilling and
freezing. Modern technologies have in no way diminished the sensory
appeal of fermented products however. This is clear from the way people
rarely enthuse over grape juice or milk as some are prone to do over the
vast array of wines and cheeses.
We now know that, in food fermentation, conditions of treatment and
storage produce an environment in which certain types of organism can
flourish and these have a benign effect on the food rather than spoiling it.
The overwhelming majority of fermented foods is produced by the
activity of lactic acid bacteria and fungi, principally yeasts but also, to
a lesser extent, moulds. Both groups of organisms share a common
ecological niche, being able to grow under conditions of low pH and
reducedaw, although only lactic acid bacteria and facultative yeasts will
prosper under anaerobic conditions. As a consequence, they frequently