Meanwhile, the amount of liberated CO2 in the
late stage of fermentation will be less than that liberated during rapid growth stage. As a result, more
oxygen will dissolve into fermentation broth through agitation and diffuse through cellular membrane to
elevate redox potential level. According to experimental observation, an uprising curve appearing during
the fermentation reveals that the fermentation is about to finish. Without supplementing extra oxidants or
reductants, redox potential measured during ethanol fermentation varies between -300 and 200 mV.
Hence, an appropriate redox potential level could be obtained and correlate to the ethanol productivity