<p style="text-align: justify;">Potassium hydrogen tartrate (KHT) is a natural compound of wine which crystallizes spontaneously. Whereas crystal occurrence can be considered as a sign of goodness in old and famous vintage wines, it is usually thought of as a serious failure for most consumers, even though it does not alter wine quality. An efficient and cheap process of wine stabilization versus KHT crystallization has to be found yet. An alternate process to physical stabilization of wines may lie in the addition of an inhibitor of KHT crystallization. Bearing this in mind, we have investigated the effect of several polysaccharides and total polyphenols fractions on KHT crystallization through the measurement of crystal appearance time (induction time) with and without any macromolecule.</p><p style="text-align: justify;">Red wines. white wines and KHT supersaturated hydroalcoholic solution exhibit different behaviours versus KHT crystallization, red wines crystallizing less easily than white wines and far less easily th an hydroalcoholic solution. Those differences can be explained by our results. The innate inhibition of red wines is the sum of the inhibiting effects of rhamnogalacturonans (RG-I and RG-II), yeasts mannoproteins present in wine and of total polyphenols. Arabinogalactans show no effect on KHT crystallization whereas rhamnogalacturonans display a peculiar concentration dependent behaviour : crystal appearance is accelerated at low concentration and slowed at high concentration. More strongly observed for RG-1I2 fractions, this feature is confirmed by a theory of crystallization in the presence of an additive. The theory predicts that RG-I has almost no effect on the nucleation phenomenon whereas RG-1I2 enhances this phenomenon. Both RG-l and RG-1I2 inhibit crystal growth by adsorption on crystal growth sites, as contirmed by single crystal growth experiments.</p><p style="text-align: justify;">Red wine tendency to be more difficult to stabilize versus KHT crystallization by cooling than white wine is due to the concentration in RG-II and in total polyphenols : low RG-II content in white wine accelerates crystal appearance whereas high RG-Il content in red wine slows crystal appearance. Thus it intensifies the inhibition due to the high total polyphenol content in red wine.</p><p style="text-align: justify;">Mannoproteins extracted from yeast cell walls inhibit KHT crystallization far more than yeast mannoproteins present in wine. However, their efficiency is reduced as temperature is lowered.</p>
<p style="text-align: justify;"><strong>Aims</strong>: Inhibition of potassium hydrogen tartrate (KHT) crystallization by carboxymethylcellulose (CMC) is tested in a model solution and in wines. Tartaric acid salt crystallization risk is assessed by computing the supersaturation, saturation temperature and excess KHT with respect to the saturation equilibrium using MEXTAR® (Mesure de l’EXces de TARtre) software.</p><p style="text-align: justify;"><strong>Materials and results</strong>: Firstly, the time for crystals to appear was recorded by monitoring the conductivity in a model solution and in a wine, and the inhibition ratio was computed. At 11,5 °C, 0,5 mg.L<sup>-1</sup> CMC inhibited KHT crystallization. The inhibitory effect increased exponentially with increasing CMC concentration and was several times greater than that of polysaccharides and polyphenols, the protective colloids in wine (Gerbaud et al., 1997). At 2 °C, 30 mg.L<sup>-1</sup> CMC had the same inhibitory effect than 10 mg.L<sup>-1</sup> at 11.5°C.Secondly, 20 red and white wines were refrigerated for 3 weeks at -4 °C with CMC or metatartaric acid. Results show that the addition of 20 mg.L<sup>-1</sup> CMC has an inhibitory effect at least equivalent to 100 mg.L<sup>-1</sup> metatartaric acid. Furthermore, for 10 wines preheated for 8 days at 30 °C and then refrigerated for 2 months at 0 °C, 5 and 20 mg. L<sup>-1</sup> CMC maintains its inhibitory efficiency, unlike metatartaric acid which is hydrolysed</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: The OIV-OENO 366-2009 and OIV-OENO 02/2008 resolutions recently authorized the use of CMC to prevent tartaric acid salt precipitation. With no impact on health, and stable under heating and in acid solution, CMC is an efficient candidate for tartaric stabilization. The optimal concentration of 20 mg.L<sup>-1</sup> (2 g.hL<sup>-1</sup>) should however be adapted to local wine storage conditions and KHT crystallization risk.</p>
<p style="text-align: justify;">La stabilisation tartrique des vins par le froid repose sur les modifications de l'équilibre chimique, cristallin ou colloïdal du bitartrate de potassium. L'élimination provoquée de l'excès de bitartrate fait intervenir ces trois mécanismes par l'abaissement de la température, l'ensemencement naturel ou exogène en cristaux ainsi que la clarification du vin et la durée du traitement. On aboutit ainsi à trois grands systèmes de stabilisation par stabulation, « par contact » ou en continu. Chacune de ces méthodes a des possibilités techniques et économiques différentes, et se trouve adaptée à des situations variées (volumes à traiter).</p><p style="text-align: justify;">+++</p><p style="text-align: justify;">Tartrate stabilization of wines by cooling is based on a modification of the chemical cristalline or colloidal equilibrium of potassium acid tartrate. The provoked elimination of excess tartrate makes use of in these three mechanisms by temperature reduction, natural or artificial inoculation of crystals as well as wine clarification and treatment length. We are thus lead to three large stabilization systems, by storage, contact or continuous process. Each of these methods has different technical and economical possibilities, and are adapted to varied situations (volumes under treatment).</p>
Des études déjà anciennes (1952) avaient montré l'effet activateur de la thiamine (ou vitamine B1) sur la fermentation alcoolique. Plus récemment des essais de laboratoire (1966) montrèrent que la thiamine, à la dose de 0,5 mg par litre de chlorhydrate, réduisait le taux résiduel des acides cétoniques dosés (pyruvique et a-cétoglutarique par exemple). Pour vérifier ces résultats plusieurs dizaines d'essais comparatifs furent mis en place durant les vendanges 1966 et 1967 dans les régions productrices de vins blancs liquoreux de Gironde (Sauternais, Premières Côtes de Bordeaux, Loupiac, Sainte-Croix-du-Mont...) et de Dordogne Montbazillac, Bergerac). Dans chaque cas, on a comparé les comportements d'un lot industriel « témoin » et d'un lot identique additionné de thiamine, à la dose de 50 mg par hl.
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