## 3 Contribution of Selected Yeasts to Emerging Winemaking Demands
### Enhancing the Aroma of Wine
Sulfur compounds are regarded as undesirable molecules, producing negative sensory attributes such as rotten egg smell [65], and even if they commonly occur at relatively low concentrations, they exhibit a very low detection threshold. It is already well established that the microbial population present in vineyards and in musts, which includes _Saccharomyces_ and NS yeasts, has a decisive influence on the final  
Figure 5: Main metabolic pathways in secondary aroma production performed by yeasts. aroma complexity of wines and, consequently, on consumer preferences [66]. In this context, \"microbial terrori\" has been recognized as the pool of native yeasts that are geographically unique and imprint a specific and distinct olfactory fingerprint on wine [67; 68]. Therefore, secondary aromas have a greater influence among the main volatile compounds that define the overall quality of wine, for which the yeast inoculum and the fermentation methodology play an essential role [69]. Despite this, the importance of indigenous isolates of _S. cerevisiae_ is also amply demonstrated during the production of wine, reflecting defined territorial characteristics [70; 71]. Several studies reported that the use of native _S. cerevisiae_ yeasts leads to wines with higher ester concentrations and sweet/fruity aromas [72]. In particular, [PERSON] et al. [73] demonstrated that the inoculation of different _S. cerevisiae_ biotypes isolated from a winery that had never used commercial starters resulted in wines with different sensory characteristics compared to wines produced with commercial starters. In detail, wines fermented with autochthonous yeasts were characterized by the presence of noticeable esters such as isoamyl acetate (banana scent) and ethyl octanoate (apple, pear, and peach aroma). Consistently, [PERSON] et al. [74] demonstrated how the use of indigenous _S. cerevisiae_ yeasts, as opposed to industrial starters, can lead to an increase in the aromatic composition regarding the production of esters like ethyl hexanoate or ethyl acetate, thus conferring an aromatic distinctive imprint linked to the geographical location [74]. Among vineyard yeasts, the NS, when inoculated in must, produces a greater range of volatile metabolites compared to those obtained solely by _S. cerevisiae_[23]. In general, according to [PERSON] and co-workers [69] and as reported in Figure 6, three types of fermentations can be distinguished: spontaneous fermentations, in which selection of native population of NS and _S. cerevisiae_ occurs, developing wines with high aroma complexity at the expense of less microbiological control; driven fermentations, in which inoculation with _S. cerevisiae_ is performed inhibiting any spoilage growth or uncontrolled fermentation at the expense, however, of less aromatic complexity; and mixed fermentation, in which an initial inoculum with selected NS strains is usually performed to enhance the aromatic profile, followed by a sequential inoculum of selected _S. cerevisiae_ starters to properly complete alcoholic fermentation; simultaneous inocula can also be performed by adding NS and _S. cerevisiae_ at the same time. It has already been ascertained how the presence of beta-glucosidase enzymes within NS yeasts is linked to the aromatic production in wines by releasing aromatic monoterpenes [75]. Strains of _Wickerhamomyces anomalus_ have been described for their high beta-glucosidase activities; in particular, in Muscat Bailey A must, the co-fermentation with _W. anomalus_, followed by _S. cerevisiae_, results in a significant increase in linalool, citronello, and geraniol contents. In a sensory evaluation, the flavor, taste, and overall preference scores of co  
Figure 6: Wine features resulted from applying different fermentation approaches. -ferrmented wines were higher than those of the control [76]. Additionally, the aroma diversity and taste characteristics (intensity, astringency, complexity, and persistence) of Cabernet Sauvignon wines were improved through co-inoculation of five _W.