# Exploitation of Three Non-Conventional Yeast Species in the Brewing Process
## 3 Results
### Fermentation Trials with the Selected Non-Saccharomyces Yeasts
#### 3.2.3 Main Volatile Compounds  
The main volatile compounds produced by _L. thermotolerans_ in pure and mixed fermentations are reported in Table 3. The results highlighted a significant increase in ethyl acetate (fruit notes) content in pure and mixed fermentations compared with _S. cerevisiae_. _L. thermotolerans_ in pure and mixed fermentations showed a significant increase in ethyl butyrate content, which is the ester responsible for the fruity or solvent aroma of beer [21], compared with _S. cerevisiae_ US-05. A significant increase in isoamyl acetate content (banana aroma) was exhibited by _L. thermotolerans_ at the 1:20 _S. cerevisiae_: _L. thermotolerans_ inoculation ratio compared with _S. cerevisiae_ in pure culture, while the concentration of ethyl hexanoate (i.e., apple, fruit flavour) decreased with increasing the inoculation ratios. The same trend was also exhibited for the linalool content. Furthermore, the citronellol content decreased in mixed fermentation at the 1:10 and 1:20 inoculation ratios, while at the 1:1 its concentration was comparable with that exhibited by the _S. cerevisiae_ starter strain. Moreover, the mixed cultures showed significant increases in higher alcohols levels with the exception of \(\beta\)-phenyl ethanol. In regard to the acetaldehyde content, the mixed fermentations at the 1:1 inoculation ratio exhibited a reduction compared with the other beers. In mixed fermentation trials, _Z. florentina_ showed a significant decrease in acetaldehyde content compared with the beer obtained with the _S. cerevisiae_ starter strain (Table 4). Regarding the ester compounds, Table 4 showed a significant increase in ethyl butyrate content at 1:20 inoculation ratio in comparison with the other trials, while ethyl acetate increases in all mixed fermentation, phenyl ethyl acetate, ethyl hexanoate, and isoamyl acetate decreases when raising the inoculation ratio. Moreover, the mixed fermentations showed a significant increase in some higher alcohols content, with the only exception of \(\beta\)-phenyl ethanol that decreased in mixed fermentation in comparison with _S. cerevisiae_ pure culture. Regarding terpen compounds, no significant differences were exhibited for \(\alpha\)-terpineol, while citronellol content significant decrease in mixed fermentation in comparison with _S. cerevisiae_ pure culture. The use of _W. anomalous_ (Table 5) in mixed fermentation led to a reduction in acetaldehyde and an increase in ethyl acetate in comparison with the beers obtained with _S. cerevisiae_. In pure fermentation, _W. anomalous_ showed a significant increase of higher alcohols (n-propanol, isobutanol, amylic and isoamylic alcohol). On the other hand, _W. anomalous_ in mixed fermentations showed higher alcohols concentrations comparable to those exhibited by _S. cerevisiae. W. anomalous_ in mixed fermentations increased the ethyl butyrate content, while ethyl hexanoate, phenyl ethyl acetate, and \(\beta\)-phenyl ethanol were decreased in comparison with _S. cerevisiae_ pure culture. In contrast, the levels of linalool did not show significant differences in the final beers. Regarding \(\alpha\)-terpineol, this aroma compound