A means to avoid the glucose effect in the production of baker's yeast from glucose and/or molasses in a fed batch culture by controlling the feed rate of fresh medium with an ad hoc measurement of the respiratory quotient, RQ, is presented. The feed rate is changed stepwise here such that the value of RQ ranges from 1.0 to 1.2 throughout the cultivation. Thus far, the specific growth rate based on the total cell mass and the growth yield obtained throughout are 0.24 hr−1 and 0.55 g cell/g glucose.
Prior to the experimental run mentioned above, equations to predetermine the feed rate and concentration of glucose in the feed are derived from the mass balance of limiting substrates (glucose). Since values of either RQ or I (Qx, oxygen consumption rate with respect to the total cell mass in the fermenter) can be measured quite easily and reliably, computer control of the fermentation in light of this information is discussed.