## 1 Introduction  
Several winemaking practices have been efficiently used to alter and improve the aroma quality of white wines [1]. Known practices, such as the use of different yeast strains, the addition of sulfur dioxide to prevent oxidation, pre-fermentation skin contact, fermentation temperature, vessel type and use of oak, among others, can produce different wine styles [2, 3, 4, 5]. A wide array of Chardonnay wine styles can be found in the market, from oaky and buttery to floral and fruity [1]. The creation of these various Chardonnay styles is due to specific winemaking processes and the volatile compounds associated with these processes, as Chardonnay is considered an aromatically neutral wine grape. For example, the presence of oak lactones and aldehydes, from the usage of oak during winemaking or aging, is responsible for the oaky and buttery styles [6]. Varietal compounds, such as monoterpenes and volatile thiols, extracted during wine processing, cause the floral and fruity aromas in white wines [7, 8]. Chardonnay grapes are grown in every wine region in the world and are an economically important wine grape [1]. In Oregon (USA), Chardonnay is the third most widely planted grape variety [9]. Depending on where the grape is grown, grape quality and the resulting wine style can vary [10]. With ever-changing, growing challenges due to climate change, understanding the cause of specific aroma quality markers and processes that can impact their formation is important for winemakers to achieve the wine quality and style they desire. Chardonnay wines can contain tropical fruit aroma characteristics (such as passion-fruit, grapefruit, and guava) [11]. Research has shown the presence of cysteinylated and glutathionylated precursors of volatile thiols in Chardonnay clusters [12]. During fermentation, these compounds are released to their aroma-active form of volatile thiols [13]. The concentration of volatile thiols in Chardonnay wines from Australia was found at concentrations well above their perception threshold [14]. Further sensory analysis revealed that these wines had tropical fruit aromas, which were well accepted by Australian consumers in their study [14]. Tropical fruit aromas have been shown to be an important fruity aroma descriptor in commercially available Chardonnay wine produced in Oregon [15]. However, the volatile composition of Chardonnay wine from Oregon and the causes of tropical fruit aroma are unclear. Volatile thiols 3-sulfanylhexan-1-ol (3 SH), 3-sulfanylhexyl acetate (3 SHA), and 4-methyl-4-sulfanylpentan-2-one (4 MSP) are typically associated with Sauvignon Blanc wines [16]. They are potent aroma compounds, found in trace levels in wine (ng/L range), and impart passionfruit, grapefruit, guava, citrus peel, and boxwood aromas [17; 18]. During fermentation, 3 SH and 4 MSP are formed from their precursors by \(\beta\)-lyase enzymes present in yeast [18]. The compound 3 SHA is formed by the acetylation of 3 SH by the yeast enzymeacetyltransferase Atf1p [18]. Strong correlations have been found between these thiols and the tropical fruit aroma of Sauvignon Blanc wines [14; 19; 20; 21]. Additional work has shown that, at concentrations found in Chardonnay wines, the volatile thiols alone impart grassy and earthy aromas and are not the cause of tropical fruit aromas [22]. A tropical fruit aroma was achieved with ester and thiol combinations or esters themselves [19; 22]. Based on these findings, winemaking processes that support the formation of thiols and esters are needed if tropical fruit aroma notes are desired in the final wine. When attempting to increase ester and thiol compounds in wine, much research has been conducted investigating yeast strains and must supplementation, as they play a fundamental role in volatile compound synthesis [23]. Despite the focus on these wine-making practices, other wine processes may alter the content of esters and thiols in wine. Fermentation temperature is known to influence the formation and retention of aroma compounds [24].