## 3 Contribution of Selected Yeasts to Emerging Winemaking Demands
### Enhancing the Aroma of Wine
anomalous_ strains with _S. cerevisiae_, and three of them showed interesting results in terms of aroma complexity. In detail, two of them exhibited higher concentrations of esters (acetate esters, ethyl esters, and other esters), as 2-phenylethyl acetate, while a third strain showed the highest contents of titratable acidity, total phenolic, total tannin, and total anthocyanin, but also a higher level of norisoprenoids, as ionone and damascenone (rose and honey flavor, respectively), carbonyl compounds, as 2-octanone and nonanal (soap and herbaceous green flavor, respectively), higher alcohols, as iso-pentanol (whiskey, malt flavor), and esters [77]. Furthermore, beta-glucosidase activity has been detected in other autochthonous wine species, as in _Pichia fermentans_, recently investigated in simultaneous and sequential fermentations with a commercial starter of _S. cerevisiae_, both in synthetic and grape juice medium. Specifically, co-inoculation showed a higher production of terpen and C\({}_{13}\)-norisoprenoids related to fruity and floral traits, exploiting glycosidase activity present in grape juice medium, probably starting with glycoside precursors present in grapes [78]. Within the _Pichia_ genus, _Pichia kluyveri_ is the only species to be commercially available, and its enoological potential is mainly related to its metabolism, which is able to release volatile compounds such as esters and thiols, especially 3-sulfanylhexan-1-ol acetate [3_SHA] (passionfruit, box tree aroma) [79], although beta-glucosidase seems to be poorly released by yeasts [80]. Moreover, a strain of _P. kluyveri_ isolated from pear showed a good production of esters, such as ethyl-acetate (banana aroma), even though their concentrations were found to be higher than their threshold (200 mg/L), thus conferring off-flavors [81]. Likewise, in Riesling Italico grape must _P. kluyveri_ yield the highest concentrations of total esters, glycerol, and i-valeric acid [82]. Therefore, when a strain is selected as a starter, its potential production of both SO\({}_{2}\) and isovaleric acid (associated with rancid cheese off-flavor) must be considered [79]. Regarding _Torulspora delbrueckii_, [PERSON] et al. [83] demonstrated the capacity of lowering the acetic acid (which confers an undesirable \"vinegary\" trait) under standard conditions. In detail, in co-culture with _S. cerevisiae_, at a 20:1 ratio, a lower production of volatile acidity (53%), and acetaldehyde (60%), has been observed compared to fermentation with a pure culture of _S. cerevisiae_. According to those results, in Chardonnay and Palomino wines obtained with sequential inocula of an industrial strain of _T. delbrueckii_, lower levels of both acetic acid and acetaldehyde were obtained, although the wines resulted in enhanced aroma intensity of fresh and tropical fruit traits [84]. In Riesling Italico grape must inoculated with single cultures of different NS strains, _T. delbrueckii_ showed a higher production of aromatic compounds, such as isoamyl acetate (banana), hexyl acetate (pear and apple), phenylethyl acetate (roses and honey), and ethyl decanoate (floral), which enhanced the aroma traits and the sensory traits of wines [85]. On the same grape cultivar, [PERSON] et al. [82] performed different sequential inocula with different native strains, among which _T. delbrueckii_ exhibited very high concentrations of higher alcohols and low acetic acid content. Furthermore, the production of glycerol, related to mouthfeel sensation [23], by _T. delbrueckii_ was also evaluated in Cabernet Sauvignon wine. The aromatic profile was explored in the red wines obtained using indigenous and commercial NS yeasts in sequential fermentation with _S. cerevisiae_ D254 starter. In detail, the fermentation performed with the autochthonous _T. delbrueckii_ was characterized by a higher amount of glycerol of about 9.73 g/L after malactic fermentation, whereas fermentation with a respective commercial strain (Prelude(tm) Chr.