## 4 Discussion
thermotolerans_ results in prolongation for a few days [28; 63; 69]. This was also the case in the present study, but only as far as the fermentation by _S. cerevisiae_ strain Sc1 was concerned. In the case of _S. cerevisiae_ strains A6Y10 and A26Y23, fermentation was accelerated. Such an effect could be attributed to the production of metabolites by the _L. thermotolerans_ strain employed that favor the development of the specific _S. cerevisiae_ strains. Since this effect is strain-dependent, further study is necessary in order to identify and elucidate it. These changes in the duration of fermentation that were observed in the present study were not accompanied by changes in the total alcoholic volume (TAV). Indeed, no statistically significant differences were observed due to the addition of _L. thermotolerans_. This concurs with the results presented by [PERSON] et al. [34], [PERSON] et al. [35], [PERSON] et al. [39], [PERSON] et al. [40], [PERSON] et al. [41], and [PERSON] et al. [43]. On the contrary, reduction of TAV due to the use of _L. thermotolerans_ was reported by [PERSON] et al. [29], [PERSON] et al. [32], [PERSON] et al. [33], [PERSON] et al. [36], [PERSON] et al. [38], and in some experimental cases studied by [PERSON] et al. [37] and [PERSON] et al. [42]. These differences can be attributed to the different metabolic capacities of the _L. thermotolerans_ and _S. cerevisiae_ strains employed in each study, as well as the hostile environment of Assyrtiko wine. The aim of the present work was to study how changing the composition of acids, through _L. thermotolerans_ utilization, could affect wine sensorial and oenological characteristics. According to our results, _L. thermotolerans_ succeeded to produce lactic acid during the first 48 h of fermentation, even in highly acidic must, resulting in enhancing total acidity at an average of 9%, abolishing the statistically significant differences that were observed in the wines made only by the _S. cerevisiae_ strains. Similarly, the statistically significant differences observed in the wines made only by the _S. cerevisiae_ strains regarding volatile acidity were also eliminated. Indeed, when _L. thermotolerans_ was utilized, the volatile acidity was increased by approximately 50%, compared to the wines made only by _S. cerevisiae_ strains A6Y10 and A26Y23, but was reduced by the same percentage, compared to the wine made only by strain Sc1. When _L. thermotolerans_ is used, an increase in total acidity, whether accompanied or not by an increase in volatile acidity, always correlates to the production of lactic acid and is very frequently reported [30; 31; 33; 37; 38; 39; 40; 41; 42; 43]. There are also cases in which no statistically significant differences in total and volatile acidity were reported when the lactic acid production was low [32; 34; 35]. However, this is the first time that a decrease in volatile acidity through the use of _L. thermotolerans_ has been reported. As in the case of the effect of the _L. thermotolerans_ strain used in the present study on fermentation duration, this effect is strain-dependent, indicating that the trophic relationships between the strains of the two species are complicated and deserve further attention. Additionally, the low pH of Assyrtiko must may induce this observed production of acetic acid by the yeast in order to succeed in its adaptation. The aforementioned changes in total and volatile acidity observed in the present study were not accompanied by a statistically significant decrease in pH value. This is in accordance with the results presented by many authors [29; 32; 34; 35; 40; 43]. However, there are also many studies employing _L. thermotolerans_ that report a statistically significant decrease in the wine's pH under high lactic acid productions [33; 36; 37; 38; 39; 41; 42]. Another interesting trait of _L.