Numerical simulations have been employed to investigate the dynamic behavior of externally excited periodic bioethanol fermentors located at different parameter spaces. The fermentors are forced in the neighborhood of a static limit point. The stroboscopic Poincare bifurcation diagrams for the fermentors show that the forcing has significant effect on the dramatic change of the dynamics of these dissipative dynamical systems and can produce fascinating rich dynamical behavior such as: frequency locking, quasi-periodicity, chaos, intermittency, interior crisis, bistability and bubbles phenomena. It is very interesting that the period doubling scenario associated with period doubling reversals (period halving) can produce the bubble phenomenon, which may act to suppress the development of chaos. It is also shown that the period doubling reversals may act to suppress the fully developed chaos. It has been shown that the chaotic regions are harmful to the efficient production of ethanol: therefore a careful control policy is recommended. (C) 2011 Elsevier Ltd. All rights reserved.