EXPLORING THE ROLE OF TRANSITION METAL IONS IN THE EVOLUTION OF ESTERS COMPOSITION OF YOUNG WHITE WINE DURING AGEING

In a climate change context and aiming for sustainable, high-quality Bordeaux wine production, this project examines the impact of grape maturity levels in various cultivars chosen for their adaptability, genetic diversity, and potential to enhance wine quality. The study explores the effects on wine compo-sition and quality through sensory and molecular methods. We studied eight 14-year-old Vitis vinifera cv. grape varieties from the same area (VITADAPT plots 1 and 5): Cabernet Franc, Cabernet Sauvignon, Carmenère, Castets, Cot, Merlot, Petit Verdot, and Touriga Nacional.

The gustatory balance of dry wines is centered on three flavors, sourness, bitterness and sweetness. Even if certain compounds were already identified as contributing to sweetness, some taste modifications remain largely unexplained1,2. Some empirical observations combined with sensory analyzes have shown that an increase of wine sweetness occurs during post-fermentation maceration³. This step is a key stage of red winemaking during which the juice is left in contact with the marc, that contains the solid parts of the grape (seeds, skins and sometimes stems). This work aimed to identify a new taste-active compound that contributes to this gain of sweetness.

The positive contribution of toasted vine-shoots (SEGs, Shoot from vines – Enological – Granule) used in winemaking to the chemical and sensory profile of wines has been widely proven. However, the combination of this new enological tool with other winemaking technologies, such as micro-oxygenation (MOX), has not been studied so far. It is known that micro-oxygenation is used in wineries to stabilizes color, improves structure or combining with oak alternatives products to achieve a more effective aroma integration of wines. For that, its implementation in combination with SEGs could result in differentiated wines.

Right after the pouring of wine in a glass, a myriad of volatile organic compounds, including ethanol, overwhelm the glass headspace, thus causing the so-called wine’s bouquet [1]. Otherwise, it is worth noting that during wine tasting, most people automatically swirl their glass to enhance the release of aromas in the glass headspace [1]. About a decade ago, Swiss researchers revealed the complex fluid mechanics underlying wine swirling [2]. However, despite mechanically repeated throughout wine tasting, the consequences of glass swirling on the chemical space found in the headspace of wine glasses are still barely known.

Over the last few years, several tools have been developed to reduce the quantity of sulfites used during winemaking, including bioprotection. Although its effectiveness in preventing the development of spoilage microorganisms has been proven, few data are available on the impact of sulfite substitution by bioprotection on the final product. The objective of this study was therefore to characterize Chardonnay wines with the addition of sulfite or bioprotection in the pre-fermentation stage. The effects of both treatments on resulting matrices was evaluated at several scales: analysis of classical oenological parameters, antioxidant capacity, phenolic compounds, non-volatile metabolome and sensory profile.