HAZE RISK ASSESSMENT OF MUSCAT MUSTS AND WINES : WHICH LABORATORY TEST ALLOWS A RELIABLE ESTIMATION OF THE HEATWAVE REALITY?

Port is a fortified wine, produced from grapes grown in the demarcated Douro region. The fortification process consists in the addition of a grape spirit (77% v/v) to the fermenting juice for fermentation interruption, resulting in remaining residual sugars in the wine and increased alcohol content (19-22%). The approval of grape spirits follows the Appellation (D.O. Port wine) rules1 and it is currently carried out based on analytical control and on sensory evaluation done by the public Institute that upholds the control of the quality of Douro Appellation wines. However, the producers of Port wines would like to have more information about quality markers of grape spirits.

In recent years, consumer demand for products without chemical additives increased, becoming a priority for the wine sector. SO₂ is widely used for its multiple properties including antiseptics, antioxidants and antioxidasics and the strategy of bioprotection in winemaking represents now an alternative to this chemical additive. In oenology, results have highlighted the interest of bioprotection to limit the development of microorganisms like Hanseniaspora uvarum and thus reduce the doses of sulphite. Indeed, this species is considered because of its acetic acid and methyl butyl acetate production, the latter can cover the varietal character of wines.

Color is one of the key elements for the marketing of rosé wines due to their packaging in transparent bottles. Their broad color range is due to the presence of pigments belonging to phenolic compounds extracted from grapes or formed during the wine-making process. However, the mechanisms responsible for such diversity are poorly understood. The few investigations performed on rosé wines showed that their phenolic composition is highly variable, close to that of red wines for the darkest rosés but very different for light ones [1]. Moreover, large variations in the extent of color loss taking place during fermentation have been reported but the mechanisms involved and causes of such variability are unknown.

Pre-fermentative skin maceration is a technique used in white wine production to enhance varietal aroma, but it can increase protein concentration, leading to protein instability and haze formation [1]. To prevent protein instability, wine producers typically use fining agents such as bentonite, before wine bottling, which can negatively impact sensory characteristics and produce waste [2,3]. The aim of this study was to understand the impact of alternative techniques such as the application of polysaccharides (k-carrageenan and chitosan) on protein stability and on the wine macromolecular composition.

Malic acid has a strong impact on wine pH and the contribution of fermenting yeasts to modulate its concentration has been intensively investigated in the past. Recent advances in yeast genetics have shed light on the unexpected property of some strains to produce large amounts of malic acid (“acidic strains”) while most of the wine starters consume it during the alcoholic fermentation. Being a key metabolite of the central carbohydrate metabolism, malic acid participates to TCA and glyoxylate cycles as well as neoglucogenesis. Although present at important concentrations in grape juice, the metabolic fate of malic acid has been poorly investigated.