Impact of heating must before fermentation on Chardonnay wines

Tannin and polysaccharide concentration and composition is important in defining the texture of red wines, but can vary due to factors such as cultivar, region, grape ripeness, viticultural practices and winemaking techniques. However, the concentration and composition of these macromolecules is dependent not only on grape tannin and polysaccharide concentration and composition, but also their extractability and, in the case of polysaccharides, their formation by yeast. Through studies into the influence of grape maturity, winemaking and sensory impacts of red grape polysaccharides, seed and skin tannins, recent research in our laboratory has shown that the processes involved in the extraction of these macromolecules from grapes and their retention in wine are very complex.

In red wines, anthocyanins evolve during the wine-making process and ageing. They react with other compounds (such as vinylphenols, acetaldehyde, pyruvic acid…) to form a stable family of compounds called pyranoanthocyanins. Furthermore, the oxidation process can modify the anthocyanic profile of a red wine. It is also interesting to evaluate the occurrence of the different subclasses of pyranoanthocyanins and to characterize their chemical properties. The first objective of this study is to evaluate the occurrence of the different groups of pyranoanthocyanins in an oxidised Merlot wine by a centrifugal partition chromatography strategy. The second goal is to evaluate their relative impact in red wines from Bordeaux region by measuring their concentrations.

Red grape pomace, a waste from wine production, can be valorised by extracting polyphenols, high-added value compounds used in cosmetics or oenology. For use at an industrial level, using green extraction techniques, pomace need to be stored before being processed. The aim of this study is to test various storage conditions in order to maintain high level of polyphenols over 180 days, while keeping storage cost economically interesting. In a first step, different storage conditions (ambient temperature or cooled (4°C) temperature, anaerobic (saturation with N2) or aerobic conditions, and addition of sulphur dioxide (SO2)) were compared on small samples (1 kg) packed in plastic pockets. The quality of storage was assessed by following the optical density of the pomace extract at 280 nm (DO 280 expressed as mg/l eq gallic acid), which is an indication of the amount of remaining extractable polyphenols.

Nutrient availability – nitrogen, lipids, vitamins or oxygen – has a major impact on the kinetics of winemaking fermentations. Nitrogen is usually the growth-limiting nutrient and its availability determines the fermentation rate, and therefore the fermentation duration. In some cases, in particular in Champagne, grape musts have high nitrogen concentrations and are sometimes clarified with turbidity below 50 NTU. In these conditions, lipid deficiencies may occur and longer fermentations can be observed. To better understand this situation, a study was realized using a synthetic medium simulating the composition of a Champagne must : 180 g/L of sugar, 360 mg/L of assimilable nitrogen and a lipid content ranging from 1 to 8 mg/L of phytosterols (mainly β-sitosterol).

In Enology the conventional processes of filtration for clarification and stabilization are giving place to alternative membrane processes, including nanofiltration (NF). Furthermore, the increased alcohol content in wines recorded in recent years became an important issue for all the main wine producing countries. Among techniques available to the wine industry to reduce the ethanol content, NF is certainly one of the newest. This study is focused on the evaluation of NF influence on wine physical-chemical composition, including mineral content, which in accordance to our best knowledge is a novelty.