Control of yeast fed-batch process through regulation of extracellular ethanol concentration

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