Part of what I was saying is that the fermentation barrels cannot be reused for other drugs. Also, with any biologically produced product in pharmaceuticals, they need to do extensive testing on each batch to ensure that there have not been any mutations or other contamination or production errors. The manufacturing of medicine is a highly regulated and monitored process that requires the manufacturer to meet a rather long list of criteria before the drug can be sold. Also, with bacterial populations, the larger the vat, the higher likelihood that a problematic mutation will occur and spread to a degree that would cause problems.