## 4 Discussion
thermotolerans_ is malic acid consumption; the majority of the strains have been reported to consume 10-20% of it, while consumption that may exceed 50% has also been reported [28; 29; 33; 34; 35; 37; 38; 39]. In the present study, malic acid consumption ranged from 9 to 23%, concurring with the aforementioned results. However, since this is a strain-dependent property, some studies reported no statistically significant reduction of malic acid [32; 34]. Several _L. thermotolerans_ and _S. cerevisiae_ strains have been sequentially employed to ferment musts from a wide variety of grape cultivars. In the majority of the cases, incorporation of the _L. thermotolerans_ strain resulted in an increase in the production of isobutanol and a decrease in the production of ethyl hexanoate, ethyl octanoate, ethyl decanoate, isoamyl acetate, and hexyl acetate [29; 32; 33; 34; 37; 38; 40; 41; 42; 43]. As far as the rest of the volatile compounds were concerned, no particular trend could be identified in the available literature, indicating the profound effect of the must composition and the metabolic capacity of the yeast strains employed. Unfortunately, no reports are available regarding the effect of _L. thermotolerans_ on the production of thiols; therefore, the reduction of their concentration, which was observed in the present study, cannot be compared to other studies. Assyrtiko wines from Santorini are characterized by sharp acidities with great aging potential. In our study, we would like to find out how changing the composition of acids in wine may impact its sensorial properties. Two panels of experts were chosen for the study; the first was a group of enologists from the region of Bordeaux in France, representing the wine experts who are not familiar with wines from Assyrtiko; the second was a group of winemakers from the region of Santorini in Greece, experts that were familiar with the variety of the volcanic terroir. Based on our results, the increase of total acidity provoked by _L. thermotolerans_ was not noticed by any of the two panels of experts, showing that 1 g/L of lactic acid does not have a significant impact on lactic or acidity perception. This result is in accordance with a previous study on the role of compound interactions on red wine taste perception, where a concentration of more than 1.4 g/L of lactic acid can contribute to a sour taste of wine [70]. Nevertheless, the expert panel of Santorini seemed to discriminate the acid sensation based on acid composition and not on total acidity, as they found the wines with less malic acid and more lactic acid to be less acidic. Recently, it has been shown that the sour taste related to the acidic attribute is mostly correlated to individual chemical compounds of the wine and not so related to the titratable acidity [71]. Additionally, the perceived acidity of wine was statistically enhanced by volatile compounds. In fact, the authors suggested cognitive interaction with taste perception, as the acids in the volatile reconstitution of model wine were unlikely to have contributed significantly to the perception of acidity [72]. As the Assyrtiko of Santorini is considered a low-intensity aromatic wine characterized by minerals, the experts of Santorini could possibly correlate the unusual, enhanced aromatic intensity of the experimental wines caused by the chosen yeast to increased acidity, indicating that the perception of acidity is a complex phenomenon that goes further than the concentration of acids.