Abstract: The present invention discloses a method of controlling the rate of carbon addition to a fermentation medium in a fed batch or a continuous fermentation medium comprising measuring the C-moles lost to carbon dioxide; measuring the C-moles added via the carbon addition; calculating the carbon dioxide feed quotient, FQ, as C-moles carbon dioxide produced divided by C-moles carbon added over a time period; and adjusting the rate of carbon addition depending of the FQ of interest, or measuring the moles of consumed oxygen; measuring the C-moles added via the carbon addition; calculating the oxygen feed quotient, OQ, as moles oxygen consumed divided by C-moles carbon added over a time period; and adjusting the rate of carbon addition depending of the OQ of interest, wherein said fermentation medium comprises a microorganism producing a compound of interest or wherein said fermentation medium comprises a microorganism producing a microorganism of interest.