This antibiotic is manufactured commercially using Penicillium chrysogenum.  The penicillin is produced in large stainless steel fermenters, which have a capacity of around 10000 dm³.

The fermenter is sterilised by steam and then loaded with a sterilised growth medium for the Penicillium chrysogenum to feed on, containing lactose, amino acids and mineral salts amongst other things.  The temperature and pH are monitored constantly to ensure that the conditions in the fermenter are optimum for the bacteria.  The fermenter is also continuously stirred and sterile air fed in.¹¹

The penicillin in the resultant broth after 160 – 200 hours of fermenting is obtained by solvent extraction.