In fermentation and in general in a bioprocess you use cells or part of cells (i.e. enzymes) to obtain the desired transformation. Biochemistry can thus give you the necessary knoweledge of how the transformation can work. In a way you change the "black box" to something more obvious

Metabolic processes, alter kinetics of enzyme reaction to get the product of choice; networking between pathways and regulating them; mechanism of reactions; acid/ basicity requirement of reactions and so on.

@ Yannis Karamanos and Ismaeel Muhamed : Although both the statement are diversified but quite relevant to their respective scopes. I am looking forward more discussions to satisfy my query.

Hello, I am explaining according to one of my experiences:

Suppose that you are producing a metabolite in your bio-reactor; let's say for example an organic acid. Then, during the growth phase and production phase, you observe that the specific rate of production progressively decreases and it causes long fermentation which is not cost-effective.

So, the problem is: long production phase.

To solve this problem, you make different hypothesizes for the decrease of the specific rate of production:

1) it is because of fermentation pH

2) it is because of inhibitory effect of the organic acid

3)...

In each case, one possible way to answer these questions is to test the influence of the factors (pH and inhibitory compounds) on the activity of enzymes involved in the production of that organic acid.

Of course there are other possibilities:

Thus, to solve the problem, you have to know the biochemical pathways, enzyme kinetics, and so on...