Providing the growth medium for the organisms

The microflora is of course one of the two key inputs to food fermentation. The other is the substrate that the organism(s) converts. With the possible exception of mycoprotein (see Chapter 17), the substrates that we encounter in this book are very traditional and well-defined insofar as the end product is what it is as much because of that substrate as through the action of the microbe that deals with it. Thus, for beers, the final product, whether it is an ale, lager or stout, a wheat beer or a lambic has clear characteristics that are afforded by the raw materials (malt, adjunct and hops) used to make the wort that the yeast ferments. The same applies for the cereal used to make bread, the milk going to cheese and yoghurt, the meat destined for salami, the cabbage en route to sauerkraut.

In all instances there are defined preparatory steps that must be undertaken to render the substrate in the state that is ready for the microbial fermentative activity. For some foodstuffs (e.g. yoghurt), there is relatively little processing of the milk. However, for a product like beer, there is prolonged initial processing, notably the malting of grain and its subsequent extraction in the brewery.

The growth substrate must always include sources of carbon, nitrogen, water and, usually, oxygen, as well as the trace elements. These nutritional considerations have already been discussed.

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