In the manufacture of penicillin, fermentation is the preferred route. The
fermentation substrate consists mainly of the sucrose found in corn steep liquor
and lactose together with minerals and phenylacetic acid. The preferred mold is
Penicillium chrysogenum and the first stage of the process is the transfer of
the mold to the fermenter from the test tube where it has been stored..
whole process is aerobic (it requires air). The fermentation is carried out over
4 or 5 days at 25-27°C.
This gives a yield of about 0.5% penicillin. The mycelium, the mold cells plus
insoluble metabolites, is filtered off in a coated drum filter. The filtrate is
adjusted the pH 2 with sulphuric acid. At this pH, the penicillin exists as an
undissociated acid; consequently, it is soluble in organic solvents. After
extraction the solution is decolourised and impurities are removed by activated
carbon in a second drum filter. The penicillin is then precipitated by addition
of a solution of potassium acetate. This converts the penicillin into a negative
ion, which makes it insoluble in the organic solvent. Inn the final steps the
penicillin is crystallized and dried.