The microbial production of penicillin has been described by different kinetic mechanisms. Even though identification of the most plausible mechanism is important for fermentation optimization, the closeness of the concentration profiles from different mechanisms in fed-batch operation makes it difficult to discriminate by equation-based methods. In this study, the method of species-complex linkage (SCL) graphs has been applied to five commonly reported mechanisms. By carrying out the fermentations in continuous mode under prescribed conditions, it is possible to discriminate among the mechanisms according to uniqueness or multiplicity of steady states. The SCL graph method requires much less computation than equation-based methods and can readily be applied even to complex networks of reactions.