# Impact of Yeast Selection on Volatile Phenol Levels of Wines Produced from Smoked-Exposed Juice
## 3 Results and Discussion
### Volatile Phenol Analyses
#### 3.2.2 Small-Scale Wine Production Trial  
In the laboratory-scale Chenin Blanc trial, VIN 13 and X16 appeared to be good candidates for further investigation, due to their association with lower volatile phenol levels, while QA23 associated with high levels of volatile phenols and could serve as a negative control (Figure 1). The correlation between the volatile phenol levels of smoked and the unsmoked wines fermented with QA23, VIN 13 and X16 during the small-scale wine production trial, is shown in Figure 3. The PCA biplot explains 93.36% (PC1 = 84.11% and PC2 = 9.25%) of the variance in the data set. Except for smoked wines fermented with VIN 13, there was a clear separation of smoked and unsmoked wines. The wines produced from smoked juice contained significantly higher levels of volatile phenols than the control wines (Figure 3 and Table S3). The same trend was observed as in the laboratory-scale yeast trial, where the volatile phenol levels varied in the wines produced with different yeasts. The control wines contained low or undetectable levels of the various volatile phenols. Smoked wines fermented with QA23 and X16, showed a positive association with guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, _o_-cresol and eugenol (Figure 3). While smoked wines fermented with VIN 13 showed a negative association with the aforementioned volatile phenols. These results are in agreement with the trend observed  
Figure 2: Principal component biplot of volatile phenols in laboratory-scale Merlot wines produced from juice exposed to smoke and fermented with different commercial wine yeasts. Mean values of three replicate fermentations and yeast details are included in the materials and methods. Abbreviation: Spon AF = Spontaneous alcoholic fermentation. in the laboratory-scale trial for the yeasts VIN 13 and QA23, where wines produced from smoke-exposed juice and fermented with QA23 was associated with high volatile phenol levels, while VIN 13 wines correlated with lower volatile phenol levels. Contrary to the laboratory-scale trial, smoked juice that was fermented with X16 resulted in wines with high volatile phenol levels. The small-scale Chenin Blanc trial showed that juice exposed to smoke resulted in wines with higher levels of volatile phenols than the control wines. This indicates that the smoke treatment applied to the juice increased the volatile phenol levels in the juice and the wines (Table S3). The results of this study are comparable to those reported by [PERSON] et al. [11], where the grapes were smoked on the vines. Guaiacol levels ranged between 5.3 and 12.9 \(\upmu\)g/L in the yeast trial conducted by [PERSON] et al. [11]. While in this study guaiacol levels in the laboratory-scale Chenin Blanc trials ranged between 10.82 and 15.15 \(\upmu\)g/L, between 6.46 and 8.21 \(\upmu\)g/L in the Merlot trial and between 1.98 and 4.76 \(\upmu\)g/L for the small-scale Chenin Blanc trial. However, the levels of volatile phenols in this study were not as high as those found in commercial wines produced from grapes exposed to wild or vineyard fires [18]. Multiple smoke applications to the juice or longer exposure times could possibly increase the levels of volatile phenols. Despite the limitation of applying smoke directly to the juice, this method is an easy and quick alternative to impart volatile phenols into juice, and can be used to investigate the effect of yeast strains, lactic acid bacteria treatments and even amelioration strategies on the levels of volatile phenols. This study showed that there are notable variations in the levels of volatile phenols produced by different yeast strains and that yeast selection plays an important role in the  
Figure 3: Principal component biplot of volatile phenols in small-scale Chenin Blanc wines produced from smoked (S) and unsmoked (C) juice fermented with three commercial wine yeasts. Mean values of three replicate fermentations and yeast details are included in the materials and methods. volatile phenol levels of wines.