Demonstraction and interpretation of the yeast lee ability to adsorb certain volatile thiols contained in wine

Yeast lees isolated from wine or a culture medium after fermentation have the particular property of being able to adsorb certain volatile thiols contained in a hydroalcoholic wine-like solution. Yeast cell-walls are also able to adsorb the same thiols when prepared by mechanical disruption of whole cells in the presence of a reducing agent such as dithiothréitol (DTT). Thiols adsorbed in this manner may be re-released from the cell-walls by the addition of DTT in the medium. On the other hand, yeast cell-walls prepared under the same conditions lose their adsorption capacity following hydrolysis with a beta-glucanase preparation able to release mannoproteins. These results indicate that volatile thiols combine with the yeast cell-walls by means of disulphide bonds with the cystein contained in mannoproteins

Dosage des composés soufrés volatils légers dans les vins par chromatographie en phase gazeuse et photométrie de flamme

Les composés soufrés volatils légers (point d'ébullition < 90°C) sont analysés par chromatographie en phase gazeuse et détection à photométrie de flamme (FPD 393 nm). En raison de la forte volatilité des substances à doser, nous avons choisi d'utiliser la technique de "l'espace de tête'; méthode simple à mettre en oeuvre et qui permet d'apprécier, avec une bonne répétabilité, des quantités inférieures au microgramme par litre. De plus, la détermination des seuils de perception des molécules dosées nous a permis d'évaluer leur incidence sur les défauts olfactifs de réduction rencontrés dans les vins

Formation des composés soufrés lourds au cours de la vinification des vins blancs secs

Les composés soufrés lourds produits par la levure au cours de la fermentation alcoolique et responsables de certains défauts olfactifs de réduction, sont fortement influencés par l'origine du raisin et les paramètres de la vinification. Pour un moût donné, les conditions de débourbage (turbidité du moût débourbé et dose de SO2 utilisée au débourbage) exercent une influence déterminante sur la teneur des vins en méthionol dont l'impact organoleptique est prépondérant par rapport à celui des autres composés soufrés identifiés. En regard de l'influence du débourbage, le rôle de la souche de levure apparaÎt moindre

Caractérisation de l'arôme variétal des vins de Sauvignon par couplage chromatographie en phase gazeuse-odométrie

Nous nous sommes intéressés à certaines nuances aromatiques caractéristiques des vins de Sauvignon. En utilisant le couplage de la chromatographie en phase gazeuse à la détection odométrique en sortie de colonne, nous avons mis en évidence dans des extraits de vins de Sauvignon une zone odorante rappellant le buis et le bourgeon de cassis. Une méthode, basée sur la mesure de la durée de perception de cette odeur caractéristique au cours de l'analyse odométrique, permet d'apprécier son intensité dans les vins. Nous démontrons ainsi le rôle de la souche de levure qui réalise la fermentation alcoolique sur l'intensité de l'arôme variétal des vins de Sauvignon

Identification of Volatile and Powerful Odorous Thiols in Bordeaux Red Wine Varieties

The use of a new technique combining low-temperature vacuum distillation with a specific chemical capture with an organomercuric compound enabled the extraction of volatile odorous thiols present at very low concentrations in the Bordeaux red wine varieties Merlot and Cabernet Sauvignon. The analysis of wine extracts by gas chromatography coupled with detection by olfactometry, flame photometry, and mass spectrometry led to the identification of three aromatic thiols: 3-mercapto-2-methylpropanol, identified for the first time in wine; 3-mercaptohexanol; and 3-mercaptohexyl acetate, already described in Sauvignon Blanc wines

Effect of vine nitrogen status on grape aromatic potential: flavor precursors (S-cysteine conjugates), glutathione and phenolic content in <em>Vitis vinifera</em> L. Cv Sauvignon blanc grape juice

Vine nitrogen status influence on S-cysteine conjugate precursors of volatile thiols, glutathione and phenolic content of the berries of Vitis vinifera L. cv. Sauvignon blanc have been assessed. Despite an increase in berry weight, the increase in nitrogen supply in the vine leads to higher cysteine precursor levels in grape juice. We also show that a late addition of nitrogen at berry set leads to a lower level of phenolic compounds in white grapes and to higher glutathione levels. Therefore, in white varieties, and particularly Sauvignon blanc, improving the nitrogen supply of the vine clearly increases its aromatic potential. However, an excess of nitrogen supply would increase the grape sensitivity to Botrytis cinerea and therefore decrease its quality

Effect of foliar nitrogen and sulphur application on aromatic expression of <em>Vitis vinifera</em> L. cv. Sauvignon blanc

Aims: It is well known that vine nitrogen deficiency can negatively impact on aroma in white wines. Soil nitrogen fertilization enhances aroma expression, but it also increases vine vigour and susceptibility to grey rot. The aim of this work was to investigate the impact of foliar nitrogen as well as foliar nitrogen and sulphur applications on aromatic expression, vigour and susceptibility to grey rot of Vitis vinifera L. cv. Sauvignon blanc. Methods and results: The impact of foliar nitrogen (N) and sulphur (S) application on aromatic expression of Vitis vinifera L. cv. Sauvignon blanc has been investigated. On a plot where vine nitrogen status is naturally low and water availability not limiting, foliar nitrogen and sulphur fertilization (10 kg/ha of N and 5 kg/ha of S) increased yeast available nitrogen content. Vine vigour and maturity level of grapes were not modified compared to the control. The wines produced from N+S vines contained more volatile thiols and glutathione. These results were confirmed by a tasting of wines produced with grapes from the experimental plots. Foliar nitrogen fertilization alone (10 kg/ha of N) also increased Sauvignon blanc aromatic expression, but less so than the N + S treatment. Conclusions: Foliar N and foliar N + S applications can enhance aromatic expression in Vitis vinifera L. cv. Sauvignon blanc wines without increasing vine vigour and infestation by grey rot. Significance and impact of the study: Vine nitrogen deficiency can negatively impact on grape aroma potential. Soil nitrogen application can increase vine nitrogen status, but it has several drawbacks: it increases vigour and enhances Botrytis susceptibility. This study shows that foliar N and foliar N + S applications can improve vine nitrogen status and enhance aroma expression in Sauvignon blanc wines without the negative impact on vigour and Botrytis susceptibility. Although this study was carried out on Sauvignon blanc vines, it is likely that foliar N or foliar N + S applications will have similar effects on other grapevine varieties containing volatile thiols (Colombard, Riesling, Petit Manseng and Sémillon)