Abstract: The invention relates to a process for the production of a fermentation broth with increased vitamin B.sub.12 content by a fermentation process carried out with a methane-producing mixed bacterium population under anaerobic septic conditions in the presence of known nutrient components and precursors. According to the invention, methanol, preferably in an amount of 0.5 v/v %, is added for some days, preferably for 3 days to the fermentation broth containing vitamin B.sub.12 used as the starting substance. Thereafter a minor part, preferably 10% of the fermentation broth, is removed and an equal volume of a nutrient broth containing the usual components in tenfold concentrations is added periodically in every 5th to 12th day, then the removal of fermentation broth is interrupted for 0 to 2 days, preferably for 1 day, and only 0.4 to 1.

Abstract: The invention relates to a method for increasing the vitamin B.sub.12 production of fermentation processes performed in a known way with a mixed population of mesophilic methane-producing bacteria under anaerobic conditions. According to the invention in an enrichment period of preferably 4 to 7 days a nutrient concentrate containing mainly inorganic ammonium compounds as nitrogen source and mainly methanol as carbon source and having a N:C weight ratio of 1:10 to 1:20, preferably 1:11 to 1:15 is added in daily portions to a fermentation broth obtained from a usual vitamin B.sub.12 fermentation process and containing living bacterium populations so as to increase the total concentration of assimilable nitrogen by a factor of maximum 4 until the end of the enrichment period, and thereafter the fermentation is terminated and the obtained fermentation broth with an increased vitamin B.sub.