A robust synthesis technique is devised for synergism and saturation systems, commonly known as S-systems, for steering steady-states of the anaerobic fermentation pathway (AFP) of Saccharomyces cerevisae. The stability, steady-state error and robustness aspects are analyzed. The synthesis problem is framed in a computationally efficient convex optimization framework. The linear matrix inequalities are formulated for minimization of steady-state error, improvement of robustness and utilization of minimum control inputs ensuring the stability of the synthetic AFP.