Investigating winemaking techniques for resistant varieties: the impact of prefermentative steps on must quality

Abstract

Resistant grape varieties are gaining interest in viticulture due to their resistance to diseases, allowing to drastically reduces pesticides in viticulture [1]. However, their adoption by the industry is hampered by concerns about the quality of their wines, which meets particular challenges due to specific biochemical traits of their berries, including high levels of proteins, high acidity and low levels of aromas [1-5].

Prefermentation treatments such as partial-grape drying and cryomaceration have been found to increase the level of thiol precursors, a group of natural grape aromas that contributes fruity and exotic notes to wine, in V. vinifera berries, prior alcoholic fermentation. Although the presence of those precursors has been reported in resistant varieties, the impact of prefermentation approaches on their concentration in musts before fermentation has not been studied.

Thus, this study examines the effect of gas maceration (CO₂, N₂) at two temperature (10 days at 25°C ; 4 days at 30 °C), partial grape drying (10 days at 25 °C), and cryomaceration (down to -20 °C using liquid nitrogen) compared to traditional skin maceration (control) on the level of thiol precursors in berries from the resistant Vitis varieties Vidal and Frontenac gris. Musts were sampled immediately after the end of treatments and after debourbage. Thiol precursors were analyzed by LC-MS/MS Orbitrap, using parallel reaction monitoring of exact masses of molecular and fragments ions, and were semi-quantified against an internal standard. An analysis of variance followed by Tuckey’s honest difference test were used to compare means while principal component analyses were conducted to evaluate the global impact of treatments on each variety.

Results showed that partial grape drying significantly increased (up to five times) the content of thiol precursors in both varieties. Gas macerations had variable effects and cryomaceration had a limited impact. In Vidal, partial grape drying specifically increased the concentration in gluthation-3-mercaptohexanol (G3MH), a precursor of grapefruit, citrus, and exotic fruits notes in wine, and glutathione-4-mercapto-4-methylpentanone (G4MMP), associated with aromas of boxwood in wine.

These results suggest that partial grape drying may contribute to improve the quality of wine made from disease resistant varieties. Further development in this project will involve the analyses of free thiols in wines made from these trials, to trace a full portrait of how prefermentative steps may contribute to improve the quality of disease-resistant wines.

References

[1] Pedneault, K., Provost, C., 2016. Fungus resistant grape varieties as a suitable alternative for organic wine production: Benefits, challenges and opportunities, Sci. Hort., 208: 57–77.

[2] Nicolle, P., William, K., Angers, P., Pedneault, K., 2021. Evaluation of flavan-3-ols and polysaccharides in musts and wines from Vitis vinifera Cabernet Sauvignon and cold-hardy Vitis sp. Frontenac. OENO One, 55:1.

[3] Nicolle, P., Marcotte, C., Angers, P., Pedneault, K., 2019. Pomace limits tannin retention in Frontenac wines. Food Chem., 277: 438–447.

[4] Nicolle, P., Marcotte, C., Angers, P., Pedneault, K., 2018. Co-fermentation of red grapes and white pomace: A natural and economic process to improve red hybrid wine quality. Food Chem., 242: 481–490.

[5] Nicolle, P., Gerzhova, A., Roland, A., Dagan, L., Delpech, S., Gagné, F., Pedneault, K., 2022. Thiol precursors and amino acids content of white interspecific hybrid grape, and impact of foliar urea and sulphur spraying on thiol precursor accumulation in berries, OENO One, 56: 3.