# Microbial Dynamics in Sour-Sweet Wine Vinegar: Impacts on Chemical and Sensory Composition
## 3 Traditional Balsamic Vinegar Yeasts and Alcoholic Fermentation  
### Zygosaccharomyces Strains  
The genus _Zygosaccharomyces_ was first described in 1901 by [PERSON]. Long after, in 2011, in the fifth edition of _The Yeasts_, _a Taxonomic Study_[23], [PERSON] and [PERSON] described six _Zygosaccharomyces_ species within the genus, namely, _Z. bailii_, _Z. bisporus_, _Z. kombuchaensis_, _Z. lentus_, _Z. mellis_, and _Z. roucxii_. Since then, novel species have been proposed, and _Z. osmophilus_ and _Z. seidelii_ are the ones most recently studied by [PERSON] and co-workers [24] and [PERSON] et al. [25], respectively. Up until the study of [PERSON] et al. [18], only the spoilage species _Zygosaccharomyces bailii_, _Z. roucxii_, and _Saccharomyces ludwigii_ were associated with balsamic vinegar samples (Table 1). [PERSON] [26] were the ones that first identified, based on morpho-physiological reports, the presence of _Z. roucxii_, and _Z. bailii_, such as their ability to grow at 1% acetic acid concentration. Afterward, [PERSON] [27] discovered the occurrence of _Saccharomyces ludwigii_ strains, together with _Z. bailii_ and _Z. roucxii_. It was also this author who first proposed the model of a two-stage fermentation: first an alcoholic fermentation, where yeasts convert sugars to ethanol, followed by ethanol oxidation to acetic acid by AAB, the biochemical process usually called acetic fermentation. In 2006, [PERSON] and collaborators [18] found that many different indigenous yeast species could be found and recovered from the traditional balsamic vinegar initial processing stage, that is, in cooked must, leading to the conclusion that the population of the yeasts is more complex than what was reported in the literature. In fact, besides _Z. bailii_, found in 41% of the samples, _Z. roucxii_, _Z. mellis_, _Z. bisporus_, and _Z. pseudorucxii_ were also found. Strains of _S. cerevisiae_, _Candidia_ (_stellate_ and _lactis-condensi_), and _Hanseniispora_ (_valbyensis_ and _osmophila_) were also detected [16, 17]. However, it is worth noting the prevalence of _Zygosaccharomyces_ strains. _Z. bailii_ is a yeast species broadly present in several processes of food fermentation, such as wine, vinegar, and tea [28, 29]. In many cases, _Z. bailii_ may be considered a contaminant yeast due to its high resistance to preservers, such as SO\({}_{2}\) and sorbate, and high tolerance to various stresses (alcohol concentration, low pH, low water activity, and presence of toxic weak acids, such as lactic, ascorbic, and acetic acid) [30, 31]. Notwithstanding their association with spoilage, their potential benefits have also been studied in some food systems [32, 33]. In wine fermentation, _Z. bailii_ in a mixed culture starter with _S. cerevisiae_ enhanced the production of ethyl esters [28]. In Kombucha and Haipao tea fermentations, _Z. bailii_ in symbiosis with other microorganisms helps obtain beverages rich in fiber, lysine, and crude protein [34]. As was mentioned before, besides strains of _Z. bailii_, in traditional balsamic vinegar processes, _Z. roucxii_ strains have also been described. In contrast to _Z. bailii_, _Z. roucxii_ can grow at salt concentrations up to 16% (\(w/v\)) and glucose concentrations up to 75% (\(w/v\)) [29, 35]. Moreover, [PERSON] et al. [36] demonstrated that _Z. roucxii_ cells, under glucose stress, decrease GCY1 (glycerol 2-dehydrogenase (NADP\({}^{+}\)) GCY1) gene expression to retain glycerol. This high sugar tolerance may explain how this yeast can be found in the cooked must of a traditional balsamic vinegar fermentation. In fact, in 2007, [PERSON] and co-workers [37] isolated two strains, coded ABT301 and ABT601, from traditional balsamic vinegar. After a multi-gene sequence approach, cloning, and sequence analysis of 5.8S-ITS rDNA, they found that their genomic background was different from the other _Zygosaccharomyces_species and could be related to _Z. rouxii_. Later, in 2013, after performing physiological and morphological tests, ABT301 was renamed _Zygosaccharomyces sapae_ sp. nov.