Characterization of the thiol aromatic potential of a new resistant grape variety: Floreal

Aims: Due to climate change and the desire to decrease enological inputs (organic farming), the vineyard has to be modified and the selection of new resistant grape varieties as an alternative is researched intensively today. From January 2018, four new grape varieties that are resistant against mildew and odium have been added to the official catalogue and are now available for planting new vineyards in France: Floreal, Artaban, Vidoc and Voltis. Floreal wines have been described as “very aromatic and very intense with specific notes of grapefruit” during tasting. Unfortunately, there is no data, either qualitative or quantitative, in literature to describe the aromatic quality of this resistant grape variety.

Today we know that the olfactory descriptor of grapefruit is mainly characteristic of 3-mercaptohexan-1-ol (3MH). To reach a deeper understanding of the aromatic potential of Floreal grapes, a combined study of the effects of both viticultural (nitrogen foliar spraying) and enological (cold lees settling) parameters has been carried out.

Methods and Results: After pressing Floreal grapes, corresponding must (with or without cold settling) was inoculated with a high b-lyase activity dry yeast strain at 20 g/hL. Temperature of fermentation was maintained close to 16 °C and we monitored the kinetic of alcoholic fermentation by measuring the rate of CO₂ release. Following this, several parameters were quantified: cysteinylated and glutathionylated thiol precursors (during grape maturation and in the must), and 3MH (in the final wine) by SIDA-UPLC-MS/MS. An innovative analysis of both reduced and oxidized forms of 3MH and 3MHA has been also performed in order to indicate possible “wine oxidizability” of such a resistant variety. 

Conclusion: 

First of all, Floreal wines have concentrations in 3MH and 3MHA close to 1300 ng/L (sum of both compounds) which is relatively low in comparison with Colombard or Sauvignon blanc from Gers or Loire Valley, respectively. Thus, Floreal wine aromaticity cannot be only explained by 3MH and 3MHA, and other powerful thiols may be implicated such as 4MMP, opening an avenue for identification of new aroma compounds. 

A surprising and interesting result was the fact that cold lees settling did not significantly improve the level of both 3MH and 3MHA in Floreal wines, whereas this technological practice is commonly used for its positive effect in non-resistant varieties such as Sauvignon blanc. 

Significance and Impact of the Study: Therefore, accurate characterization of this new grape variety and those that will be developed in the coming years represents a great challenge: adapting viticultural and enological practices to produce high quality wines in the future.