The characteristics of yeast carbohydrate metabolism in a multistage bioreactor system for rapid beer fermentation were investigated. The yield of biomass in a continuous stirred-tank reactor (CSTR) was approx 10%, whereas the yield in an immobilized yeast packed-bed reactor (PBR) was below 1.0%. The overall ethanol productivity per extract consumed was slightly higher than for conventional beer fermentation owing to the restricted growth of immobilized yeast. The organic acid composition was different from a conventional fermentation broth, i.e., higher amount of succinate and lower amount of acetate. Virtually no acetate was produced in the CSTR. Succinate was produced in both the CSTR and PBR, but the amount produced per extract consumed was approximately two times larger in the CSTR. A large amount of cr-acetolactate was produced in an early stage of a continuous operation of the PBR. However, once the immobilized yeast growth had stabilized, the productivity was lowered to approx 0.07 mg/(10 mg extract). Control of the amino acid composition of the wort fed to the PBR was not effective in repressing the production of alpha-acetolactate in the PBR. A strategy for controlling minor byproducts of carbohydrate metabolism in a multistage beer fermentation system was discussed.