## 2 Microbiota of Vineyard and Fermenting Must  
The microbiome presents in vineyards and involved in subsequent fermentation represents a complex and diverse system that includes the presence of different yeast species. In detail, the microbiota of grapes must originate mainly from grape skins and the winery environment. Yeasts are spatially distributed over grape berries and grape bunches, and their ecology varies according to the state of ripeness, as mature grapes present higher nutrient content, such as sugars [26; 27]. As a matter of fact, at harvesting  
Figure 3: Records for “wine sustainability” found in the Web of Science between 2010 and 2021.  
time, yeast populations on mature grapes are higher (\(10^{3}\) to \(10^{6}\) CFU/g) than on immature grapes (10 to \(10^{3}\) CFU/g) [28]. As a microbial reservoir, soil may affect wine's color, fragrance, taste, and quality, as well as crop production and metabolite synthesis. Gammaproteobacteria, which include _Pseudomonas_ species, and Firmicutes, which include _Bacillus_ spp., are the taxa mainly found in soil; additionally, the same _S. cerevisiae_ genotypes have been found to be shared between soil and fruit niches [29]. As extensively reported, a plethora of yeasts have been isolated from many grape varieties [30], mainly affiliated with the following genera: _Aureobasidium_, _Auriculibuller_, _Brettanomyces_, _Candida_, _Cryptococcus_, _Debaryomyces_, _Hansenispora_, _Isatchenkia_, _Kluyveromyces_, _Lipomyces_, _Metschnikowia_, _Pichia_, _Rhodosporidium_, _Rhodotorula_, _Saccharomyces_, _Sporidobolus_, _Sporobolomyces_, _Toralyspora_, _Yarrowia_, _Zygosuscus_, and _Zygosachromyces_. From an ecological perspective, apiculate yeasts, such as _Hansenispora_ spp., abound on grape surfaces and represent over 50% of the yeast population, while yeasts of the _Candida_, _Kluyveromyces_, _Metschnikowia_, _Pichia_, _Starmerella_, and _Cryptococcus_ genera are found at lower densities [31]. Despite the extremely low occurrence of fermentative species of _Saccharomyces_s on the surface of unharmed berries or even in vineyard soils, _S. cerevisiae_ is the unquestioned dominating species in the winemaking fermentation process. In addition, it is well documented that the dynamics of the yeast population during wine fermentation follow a predictable pattern of growth, with NS yeasts initially present at higher concentrations (about \(10^{4}\) cells/mL) growing during the early stages (up to 4% _v/v_ of ethanol), to be quickly replaced by strong fermentative _S. cerevisiae_ strains [32]. In particular, during the initial stage of fermentation, microbiota is dominated by naturally occurring species with low ethanol tolerance, such as _Hansenispora_, _Pichia_, _Metschnikowia_, and _Candida_, as well as _Torulspora_, _Lachanca_, _Saccharomyces_codes_, _Zygosachorumyces_, _Isatchenkia_, _Meyerozyma_, _Wickerhamomyces_, _Fibolasidium_, _Sporobolomyces_, _Rhodosporidium_, and _Vishniacozyma_, which are detected at lower densities. The diversity of the wine microbiota rapidly changes close to the conclusion of the fermentation process, with ethanol-sensitive yeasts, bacteria, and fungi largely replaced by _S. cerevisiae_[33]. To better understand the ecological background driving wine fermentation, it is relevant to predict the effects of environmental conditions on the metabolic pathway of yeasts that can switch from aerobic respiration to alcoholic fermentation. Under low O\({}_{2}\) concentrations, yeasts conduct alcoholic fermentation as pyruvate is converted into ethanol and CO\({}_{2}\), whereas at higher O\({}_{2}\) concentrations, aerobic fermentation occurs and pyruvate is converted to acetyl CoA and CO\({}_{2}\), with lower glucose consumption. Such a phenomenon, known as the \"Pasteur effect\", is mainly reported for NS yeasts that prefer oxidative metabolism.