## 3 Results
### Volatile Compound Production in S. eubayanus Isolates  
To characterize the VC production profiles of the _S. eubayanus_ strains, we analyzed the fermented word by HS-SPME-GC-MS VCs and identified VCs whose identity is unknown, rather than using internal standards for commonly known compounds. To attain this, we selected 10 strains based on the two following criteria: (i) One representative isolate from each sampling site and (ii) significantly different fermentative capacities (CO\({}_{2}\) release levels) between strains to maximize the genetic and phenotypic diversity. Therefore, we selected strains with high fermentative capacity (CL1107.1 and CL450.1), mid-fermentation capacity (CL711.2, CL216.1, CL905.1, CL602.1, and CL812.1), and low fermentative capacity (CL606.1, CL1002.1, and CL814.1) (Figure 1b). HS-SPME-GC-MS analyses using the 10 selected strains, together with the _Sp._W34/70 lager control, allowed the identification of 55 different compounds in all fermented word (Figure 2a, Table S2). Out of these compounds, 52 were found in _S. eubayanus_ strains and 22 were found in the lager strain (_Sp._W34/70) (Figure 2a). Interestingly, 32 compounds were exclusive to _S. eubayanus_ and were not detected in _Sp._W34/70. In comparison, only three compounds (ethyl hexanoate, ethyl heptanoate, and ethyl dihydrocinamate) were found solely in the commercial strain _Sp._W34/70, resulting in 19 compounds common to both species (Figure 2a, Table S2). These results demonstrate that all compounds (except ethyl hexanoate, ethyl heptanoate, and ethyl dihydrocinamate) generated by the lager strain are found in at least one wild isolate. Among all the analyzed compounds, esters represent the main fraction of the VCs identified (26 in wild _S. eubayanus_ and 15 in _Sp._W34/70) (Figure 2b,c), where 14 compounds were found in common across both species (Figure 2b). Interestingly, of the whole set of VCs identified, only a single higher alcohol, phenethyl alcohol, was detected by HS-SPME-GC-MS. In contrast, no phenolic compoundswere identified in the lager strain. However, in wild _S. eubayanus_, we discovered two different phenolic compounds: 4-vinylguaiacol (4-VG), which was found in all strains and 2,4-Di-tert-butylphenol, which was only identified in CL1002.1 and CL602.1. A negative and significant correlation was found between the number of VCs produced at the end of the fermentation process and fermentation capacity (Pearson r = -0.35, \(p\)-value \(<\) 0.05, \(t\)-Test, Pearson Correlation). In this context, strains with a higher fermentative capacity produced a lower number of (identified) compounds, suggesting that the production of a wider number of VCs is not directly related to high fermentation capacity (Figure 2d).  
Figure 1: _Saccharomyces eubayanus_ fermentation performance in lager wort. (**a**) The geographical location of the sampling sites and the strain codes from each locality. (**b**) Total CO\({}_{2}\) loss [g/L] in fermentations carried out by _S. eubayanus_ strains. Lager strain _S. pastorianus_ W34/70 was used as a fermentation control. Different letters reflect statistically significant differences between strains with a \(p\)-value \(<\) 0.05, one-way ANOVA. (**c**) Latitude and (**d**) annual average temperature at the isolation site of each strain vs. CO\({}_{2}\) loss (Pearson Correlation). Each dot represents a fermentation replicate. Three biological replicates were analyzed per strain.