At high growth rates, the biomass yield of baker's yeast (Saccharomyces cerevisiae) decreases due to the prodn. of ethanol. For this reason, it is std. industrial practice to use a fed-batch process whereby the specific growth rate, m, is fixed at a level below the point of ethanol prodn., i.e., mcrit. Optimally, growth should be maintained at mcrit, but in practice, this is difficult because mcrit is dependent upon strain and culture conditions. In this work, growth was maintained at a point just above mcrit by regulating ethanol concn. in the bioreactor. The models used for control design are shown, as are the exptl. results obtained when this strategy was implemented. This technique should be applicable to all microorganisms that exhibit an "overflow" type metab. [on SciFinder (R)]