0.44against 0.40 g g−1), while also the substrate was consumed earlierin the former case. This was attributed to the presence of bacteria(rods) grown together with the yeast strain at the early fermenta-tion stages. Bacteria apparently did not perform glucose breakdowntoward ethanol biosynthesis, and, thus, presence of bacteria (at thefirst fermentation steps), seemed to slightly reduce ethanol produc-tion, as compared with the aseptic trial. On the other hand, bacterialpopulation was almost completely eliminated with the subsequentrise in the concentration of ethanol, as the fermentation proceeded.It must be stressed that DCW production (by means of both Xmaxand YX/TSvalues) was enhanced at the non-previously sterilizedfermentations compared with the aseptic trials (Xmax= 7.3 against5.8 g L−1, YX/TS= 0.08 against 0.07 g g−1). The results with the trialunder non-aseptic conditions were considered as satisfactory, and,therefore, it was decided to proceed with the following trials withno previous sterilization of the medium.