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Detailed description of the development and use of fermenters for the large-scale cultivation of microorganisms for enzyme production is outside the scope of this volume but mention of media use is appropriate because this has a bearing on the cost of the enzyme and because media components often find their way into commercial enzyme preparations. Details of components used in industrial scale fermentation broths for enzyme production are not readily obtained. This is not unexpected as manufacturers have no wish to reveal information that may be of technical or commercial value to their competitors. Also some components of media may be changed from batch to batch as availability and cost of, for instance, carbohydrate feedstocks change. Such changes reveal themselves in often quite profound differences in appearance from batch to batch of a single enzyme from a single producer. The effects of changing feedstocks must be considered in relation to downstream processing. If such variability is likely to significantly reduce the efficiency of the standard methodology, it may be economical to use a more expensive defined medium of easily reproducible composition.

Clearly defined media are usually out of the question for large scale use on cost grounds but may be perfectly acceptable when enzymes are to be produced for high value uses, such as analysis or medical therapy where very pure preparations are essential. Less-defined complex media are composed of ingredients selected on the basis of cost and availability as well as composition. Waste materials and by-products from the food and agricultural industries are often major ingredients. Thus molasses, corn steep liquor, distillers solubles and wheat bran are important components of fermentation media providing carbohydrate, minerals, nitrogen and some vitamins. Extra carbohydrate is usually supplied as starch, sometimes refined but often simply as ground cereal grains. Soybean meal and ammonium salts are frequently used sources of additional nitrogen. Most of these materials will vary in quality and composition from batch to batch causing changes in enzyme productivity.