# Response to Sulfur Dioxide Addition by Two Commercial _Saccharomyces cerevisiae_ Strains
## 4 Discussion
It is currently unclear whether the increased production of acetaldehyde is a defense mechanism used by yeasts to survive in the presence of SO\({}_{2}\), or simply a result of the presence of SO\({}_{2}\) causing enzymatic inhibition of the products of acetaldehyde [1]. [PERSON] et al. [27] also found different compositions of volatile compounds between wines produced with and without SO\({}_{2}\). In that study, the volatile composition was also analyzed via HS-SPME GC-MS, although most compounds were combined into representative groups for analysis. It is also unclear in that study which commercial _S. cerevisiae_ strain was used for inoculation, or what concentration of SO\({}_{2}\) was added at crush. A study conducted by [PERSON] et al. [30] found that single-strain fermentations conducted by QA23 and ICV-D47 (genetically equivalent to BRL97) produced unique volatile profiles. In that study, the volatile profiles produced by QA23 were more variable among replicates than the profiles produced by ICV-D47, which is in contrast with our findings. However, it is unclear whether these fermentations were conducted in the presence of SO\({}_{2}\) or not. The production of 2/3-methylbutyl acetate, hexyl acetate, methionol, 2-phenylethyl acetate, 2-phenylethanol, and ethyl octanoate was correlated with two of the wines fermented by BRL97 in the presence of SO\({}_{2}\). These compounds produce a range of aromas, including both desirable (fruity/banana, floral/rose, honey, herby) and undesirable (fatty, and cooked potato) aromas (Table 1), and can often be found above their sensory thresholds in wines fermented by _S. cerevisiae_[64; 65; 66; 67; 42]. The wines fermented by QA23 in the presence of SO\({}_{2}\), as well as the other two wines fermented by BRL97 in the presence of SO\({}_{2}\), were positively correlated with the production of ethyl decanoate (grape) and decanoic acid (sour/rancid/fatty), and negatively correlated with the production of ethyl acetate (fruity/solvent), ethyl hexanoate (fruity/fermented pear), and ethyl 3-methylbutanol (apple/strawberry). These compounds are also often found above their sensory thresholds in wine [64; 65; 66; 68; 69; 70], and because ethyl acetate was negatively correlated with these wines, it is likely that it was found at a lower concentration, which can lend a pleasant fruity aroma to the wine. The compounds that were negatively correlated with the SO\({}_{2}\) control treatment wines (2-methylpropanol, ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, and 2/3-methylbutanoic acid) tend to give the wine roasted nuts/solvent, fruity, apple/strawberry, and butter/cheese/sweat/rancid aromas, respectively (Table 1). The wines fermented without SO\({}_{2}\) were therefore generally found to be negatively correlated with the production of compounds that produce undesirable aromas such as octanoic acid, 2/3-methylbutanoic acid, and 2-methyl propanol. Previous studies that have investigated the effects of SO\({}_{2}\) addition at crush on the sensory profiles of wines have also noted that in general, wines fermented without SO\({}_{2}\) tend to contain more fruity aromas, while wines fermented with SO\({}_{2}\) contain higher intensities of undesirable characteristics [36; 53]. Few other studies have investigated the effect of SO\({}_{2}\) addition on the volatile profiles of wines fermented by different _S. cerevisiae_ strains [25; 26; 27]. Partially in accordance with our results, [PERSON] et al. [27] also observed differences in the composition of volatile compounds in wines produced with and without SO\({}_{2}\), and [PERSON] et al. [25] also noted an increase in the production of 2-phenylethylal when SO\({}_{2}\) was added to strawberry wine fermentations. However, contrary to our results, [PERSON] et al. [26] noted a general decrease in the relative production of volatile compounds in response to SO\({}_{2}\) addition in chardonnay.