Tropical fruit aroma is highly desirable in certain white wine styles and there is a significant group of consumers that show preference for this aroma. While there is substantial work in relating tropical fruit aroma exclusively to volatile thiols, the assessment of any other compound and their interactions that may cause this aroma are yet unexplored. Previous work suggests that esters, when in combination with thiols in a wine media, play a role in tropical fruit perception as an aroma enhancer to thiol-related aroma attributes. Moreover, the highly fruity sensory profile of this family caused consumers and a trained panel to smell tropical fruit aromas in a wine model spiked with acetate and ethyl esters. In the same sensory study, samples that contained only thiols resulted in grass and earthy aromas, and not tropical fruit aromas as expected. Thus, this prior study showed that, while the presence of thiols is critical to tropical fruit perception, other aroma families, such as esters, also caused this aroma.
Considering that the presence of esters and thiols are crucial to tropical fruit aroma perception, the work herein investigated specific winemaking procedures that could increase both aroma families, esters and thiols, in white wines. Chardonnay grapes were harvested at the OSU Woodhall vineyard and processed at the OSU research winery during the 2020 vintage. The control (standard winemaking) and four treatments were evaluated: skin contact (10˚C for 18 hours), enzyme addition (β-lyase, 40 μl/L), and two fermentation gradient temperature procedures (FGT 1: start at 20˚C and after 100h change to 13˚C; FGT 2: start at 20˚C and after ~12˚Brix change to 13˚C). A full factorial design containing all possible treatment combinations was proposed, totaling 12 wines performed in triplicate, resulting in 36 microferments. To ensure that the results did not occur due to chance but due to the processes investigated, the design was fully repeated and the same procedures were followed, totaling 72 microferments. An ester method (HS-SPME GCMS) was developed to measure approximately 40 ethyl and acetate esters. The volatile thiols 3-MH, 3-MHA and 4-MMP were quantified using a method by Capone et al. (201%). A three-way ANOVA model was performed on the total concentrations of esters and thiols. Skin contact, fermentation gradient temperature and their interaction effect played a significant effect in the concentration of thiols. Significant differences were observed in skin contact and both FGT treatments for esters, but their interaction was not significant. Finally, the interaction of skin contact and FGT 1 resulted in the highest concentrations of both esters and thiols. As a future study, skin contact and FG 1 will be scaled up in a full factorial design to evaluate the sensory perception and consumer acceptance of these wines.
Authors: Tomasino Elizabeth1 and Iobbi Angelica1
1Oregon State University
*corresponding author: elizabeth.tomasino@oregonstate.edu
Keywords: Esters, skin contact, volatile thiols, fermentatiomn gradient, lyase
