## 3 Results and Discussion
In fact, it is the so-called \"ethanol make-accumulate-consume\" phenomenon. This phenomenon (in fact a metabolic adaptation \"strategy\" developed by _Saccharomyces_ strains under aerobic conditions) relies on the evolution of _Saccharomyces_ cultures against their competitors, as ethanol is toxic to most other microbes. Therefore, it is considered in a (non-aseptic) sugar- and oxygen-rich environment that _Saccharomyces_ strains eliminate their competitors by producing ethanol, but in a next fermentation step, they consume the previously generated ethanol, in order to create further DCW or maintain the already existing one (consumption of ethanol for energy of maintenance requirements) [12; 41]. Alcohol dehydrogenase (Adh) catalyzes the acetaldehyde-to-ethanol conversion in both directions. Genes ADH1 (expressed constitutively) and ADH2 (expressed only when the internal sugar concentration drops) encode cytoplasmic Adh activity [12; 40; 41; 43]. Concerning the commercial strains: Passion Fruit, Symphony and Cross X; all of these microorganisms converted glucose rapidly into ethanol with the highest quantities of glucose (_ca_ 90% \(w/w\) of the available sugar) having been assimilated within the first 24-36 h after inoculation (Table 1(a)). In the trials with Glc\({}_{0}\) adjusted to around 100 g/L, the conversion yield \(Y_{\rm EtOH/Glc}\) presented variable values, with some wild-type strains (i.e., LMBF Y-25 and LMBF Y-35) presenting excellent values (\(Y_{\rm EtOH/Glc}\)\(\geq\) 0.45 g/g, _viz._\(\geq\) 88% of the maximum theoretical yield that is =0.51 g/g [12; 13; 41; 43]). On the other hand, in similar types of experiments performed with other wild-type (\"novel\") or commercial-type _Saccharomyces cerevisiae_ strains cultured in shake-flask trials on previously pasteurized natural grape musts under aerobic conditions, the conversion achieved yields \(Y_{\rm EtOH/TS}\) ranged between 0.28 and 0.40 g/g [24], that were values slightly or somehow lower compared to those obtained in the present study (Table 1). This indicates the potential of the employed strains in the current investigation regarding the conversion of glucose into ethanol under aerobic conditions. The Crabtree-effect (_viz._ the production of ethanol from glucose or other sugar fermentation under full aerobic conditions) has been studied in other conventional but non-_Saccharomyces_ yeast strains, and the conversion yield \(Y_{\rm EtOH/TS}\) has been revealed to be 0.10 g/g for _Candida diddensiae_, 0.27 g/g for _Candida tropicalis_ and 0.28 g/g for _Candida zemplinina_[44; 45]. Adaptation to higher Glc\({}_{0}\) concentrations imposed in the medium (_viz. ca_ 200 g/L) resulted in significant quantities of assimilated glucose irrespective of the strains (commercial or wild-type ones) implicated as microbial cell factories of the process (Table 1(b)). Apart from the strain LMBF \(\Upsilon\)-10, in all other cases, consumed Glc quantities \(\geq\) 160 g/L were recorded, suggesting the potential of the employed strains towards the so-called \"very-high-gravity\" alcoholic fermentation process [12; 13; 26]. It is also interesting to indicate that despite the significant consumption of glucose that was reported for many of the trials, the conversion yield \(Y_{\text{EOH/Glc}}\) was in a number of cases lower than the respective one reported for the experiments with Glc\({}_{0}\)\(\approx\) 100 g/L (see Table 1). This has also been reported in other cases in which alcoholic fermentations had been performed in media in which all other culture parameters and components (i.e., initial nitrogen) remained constant and only glucose concentration increased [42; 43], exactly as in the current investigation, demonstrating that potentially the conversion yield \(Y_{\text{EOH/Glc}}\) is negatively correlated with the increase in carbon excess in the medium (increment of Glc\({}_{0}\) concentration in the medium with the initial nitrogen remaining constant, evidently increases the initial C/N and, thus, the carbon excess in the medium [28; 29; 42]).