# Genetic, Physiological, and Industrial Aspects of the
## 4 Industrial Application of _S. bacillaris_
### Chemical Complexity of _S. bacilaris_ and _S. cerevisiae_ Fermented Beverages  
Different complexities of fermented products can be obtained when performing single versus combined _S. cerevisiae_ and/or _S. bacillaris_ fermentations. Several authors have shown that, in laboratory scale fermentations, the concentrations of some aromatic compounds decline when using _S. bacilaris_ and _S. cerevisiae_ co-inoculums versus _S. cerevisiae_ mono-cultures (Table 2) [27; 58; 60; 63; 65; 82]. Other authors, however, have found an increase in volatile compounds when using mixed _S. bacillaris_ and _S. cerevisiae_ versus single yeast species fermentations [59]. _S. bacillaris_ has been reported to overproduce compounds such as H\({}_{2}\)S, acetoin, ethyl acetate, and terpen, which may have a negative impact on the wine organoleptic profile [23; 49; 61; 63]. The apparent contradictory results regarding the sensory characteristics and chemical complexity of these studies could be dependent on: (i) the use of different _S. bacillaris_ and _S. cerevisiae_ strains, (ii) the inoculation procedures (i.e., simultaneous or sequential inoculations), (iii) the fermentation conditions (i.e., inoculum density, temperature, SO\({}_{2}\), nitrogen and ethanol levels), and/or (iv) the grape must varieties analyzed [63; 80; 83] (Table 2). In some cases, these outcomes could be the consequence of either negative metabolic or synergistic interactions between _S. bacillaris_ and _S. cerevisiae_ strains [60; 63; 83]. Thus, a well-characterized set of co-starter strains and a proper design of the co-ferntations are essential factors to enhance or reduce the presence of particular metabolites [61; 64; 70]. Under these ideal co-fermutation conditions, the final wines would mimic the organoleptic profile of beverages obtained by spontaneous fermentations, where the local and/or regional sensorial identity of wines is enhanced [61; 65; 68]. Concerning the production of acetate and ethyl fatty esters, contradictory results have been obtained when using _S. bacillaris_ in mixed fermentations (Table 2). In fact, mixed inoculations may result in increased [60; 65; 82; 83] or reduced [58; 63] overall levels of the various esters analyzed. Similar results were observed when analyzing higher alcohols. In these studies, _S. bacillaris_ has been associated with either increased levels of total [82; 83] and specific [58; 59] or reduced [27; 65] overall levels of these compounds (Table 2). Genome comparisons between two _S. bacillaris_ strains (i.e., PAS13 and FRI751) and _S. cerevisiae_ strain EC1118 revealed that the _S. bacillaris_ branched-chain amino acid aminotransferase (BCAT) enzyme was strongly divergent from that of _S. cerevisiae_[29]. These differences in BCAT enzymes could influence valine, leucine and isoleucine degradation, and potentially the corresponding higher alcohol productions [29]. In the case of other aromatic compounds, like terpen and C-13 norisoprenoids, their presence and relative concentration levels are related to the fermentation matrix (i.e., fruits and/or fruit varietals) and strain tested [27; 58; 63; 83]. Again, either an increase or no change in their presence and relative levels was observed in _S. cerevisiae_ and _S. bacillaris_ mixed fermentations using alternative grape varietals and fruits and/or yeast strains (Table 2). Production of H\({}_{2}\)S by _S. bacillaris_ seems to also be variable and strain-specific. Different authors have reported high [17], medium [12; 17; 23], and low [23; 84] H\({}_{2}\)S production from _S. bacillaris_ strains. In some studies, the temperature of the fermentations has been considered, because production of H\({}_{2}\)S seems to increase at higher temperatures [50]. Mixed inoculations using _S. cerevisiae_ and _S. bacillaris_ result in wines with higher levels of sulfur compounds [74]. Other undesirable compounds, like volatile fatty acids, showed a reduction in mixed fermentations with _S. cerevisiae_ and _S. bacillaris_[58; 82; 83]. Low production of acetic acid by _S.