Several antibiotic fermentations have been discussed and illustrated by curves of growth and production, and the impression has probably been given that it is easy to obtain good results. In fact, it is not difficult to obtain good results, but many beginners find it hard at first. This is because it is always essential, if good results are to be obtained, to use optimal growth conditions and to inoculate with a culture in perfect condition for the job. Achieving this condition may be easy or difficult, depending on the strain being used, but it always requires attention. For optimal production it is usually also necessary to meet a number of special conditions during the fermentation; the importance of these conditions may be unexpected.

These subsidiary factors therefore deserve attention. The subject is difficult because the critical factors differ for each fermentation and have to be worked out by experience. This chapter will therefore give a number of illustrative examples that demonstrate the kind of details likely to need consideration.

The fact that it is necessary to have all stages of the inoculum in the right condition suggests that cell differentiation is the key factor (see Chapter 3.6). However, too little is known at present to be certain of the exact way differentiation brings about the observed effects, and an empirical approach is necessary.

Development work usually means testing various fermentation procedures so as to obtain the best results. These tests can only be useful if all conditions are optimal. The basic process itself must be optimised, and all subsidiary factors, such as the inoculum, must be adjusted to give ideal conditions.