Wine tasting begins with the visual, then the flavor and finally the taste. The limpidity of awine is thus part of an indissociable criteria of a good visual appreciation and thus of a good tasting. Tomake a wine clear, ...
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Wine tasting begins with the visual, then the flavor and finally the taste. The limpidity of awine is thus part of an indissociable criteria of a good visual appreciation and thus of a good tasting. Tomake a wine clear, winemakers can use "fining". Fining is a process that allows the precipitation ofparticles in suspension that cloud or will cloud the wine. This precipitation is carried out thanks todifferent fining agents which can be of protein origin (proteins of animal or vegetable origin) but alsobased on products of mineral or synthetic origin. The nature of fining agents could be a mixture or usedalone.Polyphenols are secondary metabolites widely distributed in the plant kingdom, especially in fruits,grapes and wine. They are extracted from the solid parts of the grape berry during the wine makingprocess. Polyphenols are a family of important molecules concerning the quality of wine. Indeed, amongpolyphenols, there are tannins, responsible for the tactile sensation in the mouth, and anthocyanins,responsible for the color of red wines. Mastering the impact of each oenological process, on thecomposition of these sub-families of molecules, is essential to optimize the organoleptic properties ofwines.This thesis investigates the impact of fining on the composition of phenolic compounds in red wines.As the wine before and after treatment did not always show significant differences between the finingproducts and the control wine, a method of fining precipitates resolubilization was developed toinvestigate the composition of the precipitates. This new characterization method for fining precipitateshighlight drastic differences between the clarification products. For example, some products have noimpact on anthocyanins or tannins (or very little), while others precipitate little tannins but a lot ofanthocyanins, such as bentonite, and finally, some products precipitate tannins and anthocyanins, butmostly p-coumarolylated forms, such as PVPP. Indeed, it is interesting to study the proportions ofprecipitated molecules according to the products used and compare the proportions found in the winesbefore and after treatment. It is then noticed that whatever the used fining agent, the proportions of thequantified molecules are not significantly different in the wines before and after fining, while in theresolubilized precipitates a clear difference is observed with the wines. It was shown that each finingagent used showed a typical chemical profiles typical in terms of composition. For example, concerningthe resolubilization of free anthocyanins, the malvidins present specific proportions for a fining withPVPP, or bentonite or with proteins alone. This new resolubilization technique allows the analysis andquantification of polyphenols precipitated by fining products but also by filter cakes and coloring matterprecipitates.The information concerning the different types of fining agent and doses should allow winemakers tobetter control the relative impact of each fining product on their wine. On the other hand, this thesisreport only provides knowledge about the impact of finings on the wine colloidal matrix through theprism of polyphenols. It would therefore be necessary to investigate the aromas, polysaccharides andother key compounds of the quality of the wines, which would be trapped in the fining precipitates.Moreover, the study of filtration cakes seems to be a gateway to a better understanding of their formationand thus, in the long run, to prevent their appearance in order to facilitate the filtration of wines beforebottling.
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