Improved production of ethanol (Fig. 5) must therefore have a
different explanation. One of the products of the fermentation is
carbon dioxide. Elevated concentrations of dissolved carbon dioxide
are known to inhibit S. cerevisiae [45,46] and have a similar
effect on K. marxianus [32]. Improved gas–liquid mass transfer may
have contributed to improved removal of the highly soluble carbon
dioxide from the broth to enhance the ethanol productivity relative
to control. Rapid desorption of carbon dioxide from a fermentation
broth commonly produces foaming, as it does in a glass of
beer. The fermentation broth was indeed observed to foam within