Graduate Thesis Or Dissertation
 

Tropical Fruit Aroma in Chardonnay: Impact of Fermentation Techniques on Volatile Ester and Thiol Concentrations, Tropical Fruit Aroma Perception, Preference, and Emotional Response

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/xg94hz47n

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  • Tropical fruit aromas are prominent in wines like Sauvignon Blanc, one of the most abundant white wines in the United States. With high consumer interest for these aromas, it has become increasingly important to understand the factors that influence the desired tropical fruit aromas in white wines. Understanding the causes of tropical fruit aromas in wine and the processes that alter these compounds is necessary to ensure winemakers have the tools to consistently achieve the desired quality of tropical fruit aroma. By adapting their winemaking approach, winemakers will be able to meet the needs of the consumer consistently year to year. The first study of this thesis looked to determine if Chardonnay wines with different tropical fruit aromas influenced wine consumers preferences and emotional responses. Four wines were produced using different winemaking practices (Control = control fermentation at 13℃ with no skin contact, SC = fermentation at 13℃ with 18 hours of skin contact, FG = fermentation temperature gradient by time (20℃ for 4 days then reduced to 13℃) with no skin contact, SCFG = fermentation temperature gradient by time with 18 hours of skin contact). Liking, using a 7-point Likert scale, showed there was not a significant difference between treatments. Emotional response, using a 5-point Rate-All-That-Apply (RATA) scale, showed significant differences for ‘calm’ and ‘disgusted’ emotions. Check-all-that-apply (CATA) for aroma descriptors showed that the control is described using aromas of passionfruit, lychee, and pome fruit; SC had aromas of grapefruit and floral; FG was described as having melon, lychee, and pineapple aromas; and SCFG was described with aromas of lemon/lime, mango, and guava. Positive emotions were associated with fruity aromas in the wines, although no difference in liking was found. Understanding how tropical aromas are perceived by the consumer can allow winemakers to produce tropical fruit aroma Chardonnay wines consistently year to year. The second study focused on scaling up previous work with micro fermentations to a size large enough to perform sensory analysis to determine if wine making treatments could achieve different combinations and concentrations of thiols and esters and if these caused a tropical fruit aroma in the final wines. Previous work using micro fermentations showed that fermentation temperature gradients and time on skins resulted in an increase in thiol and ester compounds post fermentation. These compounds are known to cause tropical fruit aromas in wines. This work aimed to scale up these fermentations/operations to determine if the desired aromas could still be achieved. The four treatments tested (as listed above) were control, SC, FG, and SCFG. Chemical analysis and descriptive sensory analysis were conducted to determine the effects on the composition and aroma profiles of these wines. Thiols were measured using LC-MS/MS and esters using HS-SPME-GCMS. Wine treatments SC and SCFG were found to have higher levels of esters and thiols. Check-all-that-apply (CATA) showed different prominent aromas for each wine treatment, with pome fruit, stone fruit, pineapple, honeysuckle, honey, and passionfruit being the most perceived aromas. Descriptive analysis (DA) showed that SC was significantly different from both FG and SCFG. SC presented the most tropical fruit aromas, SCFG presented more stone fruit, and FG presented more honey and lemon/lime. Chemical analysis revealed that SC and SCFG are the main producers of esters and thiols. SC showed the highest levels across all thiols and acetate esters. SCFG displayed high levels of 3MH and 3MHA, along with ethyl esters. Together this research shows that skin contact and a fermentation temperature gradient have a positive effect on tropical aroma in Chardonnay wines. Understanding the link between wine processing and quality and consumer desires is important as wine is subjected to different environmental conditions each year, and consistency can be difficult to achieve. These conditions of winemaking using skin contact and fermentation temperature gradient would be recommendation for winemakers looking for this tropical fruit aroma sensory signature in Chardonnay wines.
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