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Grapevine curettage was re-introduced in France in the early 2000s, and is important for facilitating recovery of plants from esca disease. This surgical practice involves removal of deadwood of vines with leaf symptoms, focusing on white rot generally observed at the centres of grapevine trunks. Assessment of the efficacy of this practice was initiated in the Bordeaux region in 2014. One ‘Sauvignon Blanc’ vineyard severely affected by esca was initially surveyed in the summer of 2014, to identify and treat vines with esca foliar symptoms. Annually thereafter, from 2014 to 2018, selected vine stocks were curetted. Two other ‘Sauvignon Blanc’ vineyards also displaying high levels of esca damage were added to the study in 2015 and 2016. Curettage treatments ceased in 2018, resulting in 11 trials (vineyard × year combinations). In total, 856 vines (422 curetted and 434 control vines) were then surveyed annually up to 2021, for assessments and comparisons of esca development. At each site, plants with esca symptoms recovered well after curettage: on average 85% of all curetted vines became asymptomatic the year immediately after the treatment. Six years after treatment, for curettage campaigns carried out in 2014 and 2015, more than half of the curetted vines were symptom-free, whereas

Abstract Background Fermentation completion is a major prerequisite in many industrial processes involving the bakery yeast Saccharomyces cerevisiae. Stuck fermentations can be due to the combination of many environmental stresses. Among them, high temperature and ethanol content are particularly deleterious especially in bioethanol and red wine production. Although the genetic causes of temperature and/or ethanol tolerance were widely investigated in laboratory conditions, few studies investigated natural genetic variations related to stuck fermentations in high gravity matrixes. Results In this study, three QTLs linked to stuck fermentation in winemaking conditions were identified by using a selective genotyping strategy carried out on a backcrossed population. The precision of mapping allows the identification of two causative genes VHS1 and OYE2 characterized by stop-codon insertion. The phenotypic effect of these allelic variations was validated by Reciprocal Hemyzygous Assay in high gravity fermentations (> 240 g/L of sugar) carried out at high temperatures (> 28 °C). Phenotypes impacted were mostly related to the late stage of alcoholic fermentation during the stationary growth phase of yeast. Conclusions Our findings illustrate the complex genetic determinism of stuck fermentation and open new avenues for better understanding yeast resistance mechanisms involved in high gravity fermentations.

The re-emergence of Grapevine Trunk Diseases (GTDs), mainly Esca, has been observed in most of the world’s vineyards during the last two decades. Development of necrosis in grapevine wood, especially white-rot, is typically associated with Esca-diseased plants. One of the different methods being used in attempts to eradicate GTDs is curettage. This old cultural practice, which consists in surgically removing the necrotic wood, specifically white-rot, retaining only the non-necrotic tissue of Esca-diseased grapevine, is used in some European vineyards (Spain, France, Italy, Portugal), and is being increasingly reintroduced since 10 years ago in France. We, therefore, wanted to study the effect of curettage on vigour, fertility and berry quality, and year after year plant recovery. Our study synthetizes a 3-year experiment on Esca-diseased cv. Sauvignon blanc grapevines curetted in a commercial plot in the Bordeaux region. Asymptomatic control grapevines were compared to Esca-diseased grapevines without curettage (with typical foliar symptoms), and with curetted Esca-diseased grapevines (without foliar symptoms). Even if the curetted grapevines recovered lower vigour and fertility than the control plants, their grape berry quality was comparable, unlike for Esca-diseased grapevines. This cultural practice proved particularly effective in helping Esca-symptomatic grapevines to recover asymptomatic after treatment. Over time, curettage induces the resilience of grapevines, allowing them to recuperate their full physiological functioning, thereby compensating for Esca’s detrimental impact on berry quality.

Aging in barrel affects the sensory characteristics of wines and modifies the sweet taste in particular. Using an inductive approach, several sweet triterpenes, QTTs, have been identified in oak. Quantitative analysis has shown a significant species effect: sessile oak releases more sweet triterpenes while pedunculate oak is richer in bitter triterpenes. It is now possible to differentiate the two species on the basis of their triterpene composition.

Aim: The aim of this study was to elucidate how an initially neutral Merlot must resulted in a wine with characteristic aromas of red- and black-berry fruit, focusing on the respective contributions of yeast metabolism together with grape juice, pulp, and skins. Methods and Results: Sensory analyses were performed on Merlot grape skin maceration models, based on observations in the winery. Initial findings revealed that strong fruity nuances appeared during pre-fermentation maceration. In the maceration models used, the development of aroma of red- and black-berry fruit systematically paralleled the growth of the yeast population. The respective roles of grape skins and yeasts were investigated throughout the alcoholic fermentation of model musts with addition of Merlot skins or Merlot skin extract in ethanol. The aromatic nuances revealed by alcoholic fermentation in a must alone had no specific white-, rosé-, or red-wine character. In contrast, wines made by microvinification with grape skins and/or grape skin extract in ethanol had a clear, intense aroma of red- and black-berry. Microvinification with both Merlot skin extract and grape skins revealed the most intense fruity character. Conclusions: Inodorous skin constituents produced a specific aroma of red- and black-berry fruit after alcoholic fermentation by yeast. The physical presence of grape skins during fermentation enhanced the intensity of the fruity nuances obtained. Significance and impact of the study: The study established, for the first time, the existence of inodorous constituents in Merlot grape skins, extractible by ethanol and transformed by yeasts to produce a specific aroma of red- and black-berry fruit in the finished wines.

Aims: The first aim of this investigation was to determine whether red- and black-berry fruit aromas were specific to red wines. The second aim was to study their contribution to the red Bordeaux wine concept. Methods and results: In experiment 1, red wines were presented to expert assessors in dark, then in clear glasses. Assessors selected wines where they detected specific red-/black-berry aromas and then rated the perceived intensity. Results showed a statistically significant impact of visual input on both detection and intensity rating of red-/black-berry aromas in red wines. As part of experiment 2, both red and white wines were rated using dark glasses only. Globally, red-/black-berry aromas were shown to be more specific to red wines. Finally, in experiment 3, red Bordeaux wine experts assessed the degree to which 21 wines (9 red Bordeaux wines, 8 red wines of various origins and 4 white wines) corresponded to their own red Bordeaux wine concept, and then evaluated the intensity of 4 fruity descriptors they had detected in these wines. The results revealed that the expert assessors shared coherent olfactory concepts of red Bordeaux wines, which enabled them to distinguish the red Bordeaux from the other wines presented. Conclusions: The existence of a red-/black-berry character specific to red wines was demonstrated. Moreover, it was shown for the first time that red Bordeaux wines tend to have their own sensory space. The distinctive character of these wines was found to relate to « black-berry » and « jammy-fruit » olfactory descriptors. Significance and impact of the study: This study clarified our knowledge of the fruity olfactory descriptors specific to red wines in general and red Bordeaux wines in particular.

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).

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.

An approach consisting of controlling yeast inoculum to minimize volatile acidity production by Saccharomyces cerevisiae during the alcoholic fermentation of botrytized must was investigated. Direct inoculation of rehydrated active dry yeasts produced the most volatile acidity, while a yeast preparation pre-cultured for 24 hours reduced the final production by up to 23 %. Using yeasts collected from a fermenting wine as a starter must also reduced volatile acidity production. The conditions for preparing the inoculum affected the fermentation capacity of the first generation yeasts: fermentation duration, sugar to ethanol ratio, and wine composition. A pre-culture medium with a low sugar concentration (< 220 g/L) is essential to limit volatile acidity production in high sugar fermentations.

Yeast strains contribute to the oenological and sensorial characteristics of the wines they produce. The present study was performed to determine the influence of Saccharomyces cerevisiae strains on the composition and sensorial properties of Albariño wine. The must obtained from Albariño grapes was inoculated with 12 different yeast strains isolated from a single winery in Galicia, Spain. Chemical and sensorial analyses were performed on the final wines, which differed depending on the yeast strain used.

We measured ability of some indigenous Saccharomyces bayanus var. uvarum wine yeasts to release volatile thiols from their S-cysteine conjugate precursors, odorous compounds responsible for the characteristic aroma of Sauvignon blanc wines. We also made interspecific hybrids between Saccharomyces cerevisiae and Saccharomyces bayanus var. uvarum strains and verified their hybrid origin with karyotypes and MET2 PCR-RFLP analysis. As compared to the parents, some hybrids could release high amounts of volatile thiols from the S-cysteine conjugate precursor without producing excessive amounts of β-phenylethyl alcohol and its acetate. One hybrid was retained for industrial production under a dry form and successfully compared with Saccharomyces cerevisiae strains in experimental tests in different cellars.

Twenty rose and ten claret A.O.C. Bordeaux wines made from Cabernet Sauvignon, Cabernet franc and Merlot grapes were separately tasted by the same jury of ten professionals. They were asked to classify the wines according to the intensity of the fruity character. The fruitiest sample was given first rank. The wines’ bdamascenone, b-ionone, phenyl-2-ethanol, isoamyl acetate, phenyl-ethyl acetate (APE), 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (A3MH) contents were also measured. The higher the latter three compounds' values, the higher the wines’ fruity character. Highly significant correlation were found between the sensorial analysis results and these compounds contents. In order to confirm the 3MH, A3MH and APE contribution to the fruity aroma of rose wines, a tasting has been carried out. For this, these three compounds were added to a rose wine up to the concentrations found in the wine judged the fruitiest by the tasters. 100 % of the tasters identified the supplemented glasses, and 90 % prefered the supplemented wine. This second experiment clearly demonstrate that 3MH, A3MH and APE can be considered key components of Bordeaux rose wines’ fruity aroma. The production of APE by yeast has been known for a long time. The 3MH is present in must under cysteinylated precursor form. The transformation of the precursor into aroma is made by the Saccharomyces cerevisiae yeasts during alcoholic fermentation. Thus the choice of yeast strains has a decisive impact on the fruity aroma of Bordeaux rose and claret wines.

Vine sprayings with fungicides is necessary in most vineyards of the world since the second half of the 19th century in order to control parasitic fungi particulary downy mildew (Plasmopara viticola) and powdery mildew (Uncinula necator). During more than 50 years, copper and sulphur fungicides have been the only agents active against these deseases. Since the 50th, losts of organic products have been developed to control parasitic fungi. Meanwhile, the viti-vinicultural sector has progressively taken in consideration indirect consequences of vine sprayings on toxicological, environmental and oenological aspects. About oenological aspects, numerous publications concern the consequences of vine sprayings on fungicide residues in must and wines as on development of fermentations, volatile sulphur defaults in wines as on grape maturation and wine quality. However, studies concerning the consequences of fungicide sprayings, against downy mildew, on grapes and wines composition have been realized using reference vines sprayed with organic fungicides. Most part of Chilean vineyard is not concerned by the downy mildew. So, it is possible in this vineyard to keep a reference vine without any spraying against this fungus and to compare grapes and wines composition obtained from vines sprayed with fungicides or not. Close to Santiago de Chile, cabernet sauvignon vines were sprayed during all vegetative period with different fungicides (only folpet, folpet then copper, folpet and fosetyl-Al mixture) following a random-block scheme (Fischer blocks) with three repetitions for each fungicide spray. Grapes and wines composition were compared with those from a reference plot without any spraying against mildew. Fungicide sprayings didn’t significantly modify sugar composition, nor titratable acidity and pH during cabernet sauvignon grapes maturation unless it should be noted that the percentage of veraison was significantly higher in the initiation of grapes maturation. Some significant variations in 3-mercaptohexanol content, a varietal thiol of cabernet sauvignon wines, after alcoholic and malolactic fermentation were noted with copper sprayings. This result from copper reactivity with thiols. Variations in anthocyanin concentrations in grapes and wines were also observed but vine sprayings didn’t give anthocyanin concentrations at harvesting in grapes or in wines after vinifications at lower level than in reference grapes and wines. Globally, in this experimentation, fungicide sprayings didn’t lead to a significant modification of wines composition.

Vine water status is an important factor in grape quality. High tannin and anthocyanin content in red grape berries are related to moderate vine water deficits. Hence, a simple and sensitive indicator is required to determine vine water status and especially water constraint. Pressure chamber allows a quick and easy to practice determination of water status in the vineyard. Three applications of pressure chamber are known: predawn leaf water potential (ΨB), leaf water potential (ΨF) and stem water potential (ΨT). Only ΨB and ΨF are widely used on vines. In this survey ΨB, ΨF, ΨT and transpiration flow were measured on mature leaves to determine non-irrigated vine water status in field grown vines during the growing season. In California as well as in France, stem Ψ was the most discriminating indicator for both moderate and severe water deficits. In every plot surveyed ΨT was much better correlated to leaf transpiration than ΨF. Moreover, ΨT revealed nascent water deficit earlier than ΨB did. Among the three application of pressure chamber, ΨT was the only one to indicate short term water deficit after a rainfall. Hence, ΨT appears to be a useful indicator for grapevine management in both non-irrigated and irrigated vineyards.

Five indicators of vine nitrogen status were compared for their accuracy to differentiate two levels of nitrogen fertilization (0 and 45 kg N / ha) : petiole total nitrogen content, leaf blade color intensity measured by a device called “N-tester”, grape juice total nitrogen content, grape juice assimilable nitrogen content and grape juice ammonium content. Differences in must total nitrogen content and must assimilable nitrogen content were highly significant between fertilization levels. They can be considered as two powerful tools to assess vine nitrogen status. Levels of must total nitrogen content and must assimilable nitrogen content were highly correlated. Mineralizing must in order to measure its total nitrogen content is difficult, mainly because of the presence of large amounts of sugar. This operation can take more than 12 hours and it can fail because of caramelization and the appearance of foam. We propose mineralizing must by means of microwave. Complete mineralization was obtained in only one hour. No foam or caramelization was observed on any of the samples mineralized. Vine nitrogen uptake is likely to vary to a considerable extend with soil parameters, even if no nitrogen fertilization is applied. Figuring among those parameters are: soil organic matter content, organic matter C/N ratio and soil organic matter turnover. The latter depends mainly on soil temperature, soil aeration, soil pH and soil moisture content. Differences in vine nitrogen status depending on the soil type were clearly evidenced by measuring must total nitrogen and must assimilable nitrogen at ripeness. Limited nitrogen uptake, as a result of particular soil conditions, can limit vine vigor and be a quality enhancing factor in red grape production. This emphasizes the role of moderate environmental stress in the production of high quality potential grapes.

The influence of four industrial and indigenous yeast strains on the sulphur dioxide combinations of wines obtained from noble rot and raisining grapes is studied in different growth of the Sauternes area and one growth in the Jurançon area. The analysis of ketonic compounds (pyruvic acid and 2-oxo-glutaric acid), acetaldehyde and PC50 on the wines clearly showed significant statistical difference between the yeast strains for the sulphur dioxide combination. By adding the same dosage of sulphiting, the free SO2 levels are variable depending on the yeast strain used. One strain (Zymaflore ST), isolated from a spontaneous fermentation of a botrytised must, giving wines with low PC50 values, is well adapted for the noble rot must vinification. The choice of the yeast strain is a parameter of importance to limit the sulphur dioxide amount in the wines.

Différents essais de laboratoire sont utilisés depuis longtemps pour évaluer le risque d'apparition d'un trouble protéique. Les auteurs comparent ces différents tests en utilisant les méthodes récentes de mesure de la limpidité (néphelométrie) et de dosage des protéines (CLHP). Les résultats obtenus montrent que le test à la chaleur (80° C-30 mn) reste l'essai de laboratoire le plus fiable, car il est simple à mettre en oeuvre et il se rapproche le plus des conditions d'apparition des troubles protéiques dans la pratique. +++ Various laboratory stability tests have been used for a long time to check the risks of protein turbidity. The authors have been comparing those different tests with the help of more modern methods of measuring out cloudiness (nephelometry) and protein (HPLC). Six tests were examined : - The test consisting in heating for 5 minutes at 80° C in a double-boiler. - The test consisting in heating for 30 minutes at 80° C in a double-boiler. - The test consisting in heating for 10 days at 35° C in an oven. - The adding of 0.5 9 of tannin per litre. - The adding of a reagent to phosphomolybdic acid (bentotest). - The adding of trichloracetic acid. The results are as follows : - For the tests involving heat, the longer the heating at 80° C, the higher the measures of the turbidity are; the cloudiness observed for the test consisting in heating at 35° C for 10 days is quite important. If the results obtained with these heating tests are to be compared to the real protein values, the most efficient test consists in heating 30 minutes at 80° C. - For the tests consisting in adding tannins, a high variation of turbidity values must be related to the results obtained through high performance liquid chromatography. Moreover, the important cloudiness observed when the tannins were added does not correspond to the small difference observed between the chromatograms of the wine streated with the tanins and those of the original samples. - The reagent to phosphomolybdic acid (bentotest) and the trichloracetice acid test create an important turbidity. After chromatographic examination, the use of these reagents proved to be acting more thoroughly on every sort of protein than the use of heat in the heating tests. For two out of the four wine-samples examined, the bentotest was more drastic than the addition of trichloracetic acid. As a conclusion the heating test (80° C for 30 minutes) remains the most reliable laboratory test, because it is sample and easy to make; it is also very close to the conditions in which protein turbidity may appear in reality.

This study is dedicated to quantification, by gas chromatography combined with mass spectrometry, of some volatile compounds founded during ageing of sweet natural wines. Besides determination of the thresholds olfactory perception enable us knowing better the more active compound in sweet natural wines aroma. The results enable to know better volatile compounds which are able to produce ageing aromas characteristic of sweet natural wines. These products are always rich in sugar and grown up in a more or less oxidising environment. Logically, many of the compounds identified in this work (derived furanic compounds and many others) are Iinked with chemical like Maillard reactions between sugars and amino-acids. Others compounds as a sotolon need oxidising phenomena to increase in the environment. Comparatively, oldest Port wines have been analysed. The compounds measured in these Port wines also exist in French sweet natural wines of type Banyuls and Rivesaltes, keeped under oxidising environment. But the dillerences of concentrations in some compounds discriminate them from the Port wines.

The aroma of the sweet fortified wines is often characterised by the « rancio » descriptor. According to the mode of conservation and the type of vine, the intensity of « rancio » character inay vary notably. The molecule responsible for this aroma in sweet fortified wines has been identified to the sotolon. According to its content, this molecule can influence differently the aroma of wines. Less than of 300 µg/1, sotolon takes part of « prune » aroma, whereas between 300 and 600 µg/1, it is responsible for the « dried prickly-pear, dried fruit » aroma. More than of 600 µg/1, the sweet natural wines are characterised by « rancio » character. An oxidising conservation is essential for high content of sotolon. An accidental oxidising during ageing in bottle, according for instance with a poor quality of the cork, may increase the formation of this compound in some sweet fortified wines. With the same âge and for the same level of the oxidation, the red sweet natural wines have always a lower sotolon content than the whites. The presence of polyphenolic compounds, by slowing down oxidising phenomena and by reducing the accumulation of ethanal essential for the sotolon formation, explains the lower content of this molecule in the red wines. The sotolon formation in the sweet natural wines has been studied through many experimentations on wines and model solutions at the laboratory and the winery scales. We show that the formation of sotolon during conservation and oxidising ageing of sweet natural wines essentially depends on chemical phenomena.

This work is dedicated to the study of volatile compounds responsible for typical aroma of sweet natural wines, from non Muscat varieties, after ageing. The descriptive sensorial analysis and the modern technics of gas chromatography analysis combined with different detection modes (olfactory detection, and both mass and infrared spectrometry) are used for studying the relationships between the consensual descriptors of the aroma and the volatile substances identified in these wines. The relationships between the data (coming from the descriptive tasting and the volatile compounds and sweet-smelling) are studied thanks to correspondences factorial analysis and principal components analysis. Many substances take part in the characteristic odour of the natural sweet wines after ageing. Several volatile odorous compounds identified by the combination of gas chromatography with olfactory detection and mass spectrometry are signaled for the first time in sweet natural wines in this work. However, many of these substances were known in the aroma of several sweet products. Furaneol is always associated with « honey» aroma. Cyclotene (2-hydroxy-3-methyl-2-cyclopenten-I-one), maltol (3-hydroxy-2-methyl-4(H)-pyran-4-one), dihydromaltol (2,3-dihydro-5-hydroxy-6-methyl-4(H)-pyran-4-one), hydroxymaltol (3,5-dihydroxy-2-methyl- 4(H)-pyran-4-one) and DDMP (2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one), already known for taking part in « toasty» aroma of heated wood, have been identified in old sweet natural wines extracts, which had never been conserved in a wood barrel. Homofuraneol (5(or 2)-ethyl-2(or 5)-methyl-4-hydroxy-3(2H)-furanone), characterised by« caramel» aroma, is found only in young red sweet natural wines. Sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) seems to be characteristic of white swect natural wines. The 5-ethoxymethylfurfural, characterised by a« white bread» aroma with « sharp » and « fruity » shades, have already been found in old red wines. The γ-octalactone and γ-nonalactone, characterised by a strong fruity odour of « coconut », « peach » and « almond », are al ways associated with the « dried-fruits » characteristic aroma of white and rather old sweet natural wines, Pantolactone (3,3-dimethyl-2- hydroxy-γ-butyrolactone) is a quantitatively major compounds in old sweet natural wines, associated in principal component analysis with « plum » aroma in the oldest sweet natural wines. The results enable to know better the volatile compounds which are able to produce ageing aromas charactcristic of sweet natural wines. These products are al ways rich in sugar and grown up in a more or less oxidising environ ment. Logically, many of the compounds identitied in this work (pyranones, furanones and derived esters) seem to be linked with chemicallike Maillard reactions between sugars and amino-acids. Others compounds (sotolon and γ-Iactones) need oxidising phenomena to increase during the ageing of the wines.

This note presents the first results of a work conducted on the future of the folpet grape must and the relationship between the behavior of the fungicide and the onset of fermentation alcoholic.

Some mannoproteins which are extracted by enzymatic hydrolysis of yeast's cell wall with the aid of commercial preparation composed with beta-glucanases (Glucanex™) inhihits the tartaric acid's salt breakdown in model solution as well as in wines for an addition between 10 and 25 g/hl. On the other hand, heat extracted mannoproteins arc inactive on the tartaric precipitation stabilization. Furthermore, the crystallization inhibitor activity of the enzymatic extracted mannoproteins is due to the presence of sharply glycosylated mannoproteins of mediummolecular weight (30 to 50 kda) which are not heat extracted. That is why the heat extracted mannoproteins are inactive. The enzymatic extracted mannoproteins are produced at a pilot plan. This preparation (Mannostab™), soluble in wines, colourless and without any flavour, stabilize with the same efficiency than a freeze treatment and this effective live is superior to the metatartric acid. Moreover, the necessary steps were been taked to permit experimentally this new product : Mannostab™

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.

The incidence of cupric sprayings using a commercial formula of Bordeaux mixture (containing 20% of copper sulphate or an organic fungicide), on Sauvignon grapes composition and wines varietal aroma, has been studied in three areas of the Bordeaux region (Entre-deux-Mers, Graves, Médoc). Copper content has been noticed to increase in the clarified juices in all cases after these treatments, values ranging from 0,3 mg/l to 14,5 mg/l, whereas natural copper content did not exceed 0,4 mg/l. The value of residual copper by treatment was found to be significantly different from one year to the other (2 to 3,5 mg/l in 1993, 0,3 to 0,9 mg/l in 1994 and 0,7 to 0,9 mg/l in 1995) mainly due to the grapes composition and the different climatic conditions, whereas for the same year in the three different areas, this value was almost the same. The operation known as «skin contact» during which juices were left with their skins under CO2 at 10°C, during 18 hours before pressing, was found to decrease copper content in the clarified juices from 60 p. cent to 80 p. cent, whereas immediate pressing of grapes led to a decrease of only 20 p. cent ; the combination of copper during skin contact with glutathione, which is present in Sauvignon grapes, is a possible explanation. Under the ripening conditions of Bordeaux's oceanic temperate climate, we have noticed that even one single spray with a commercial formula of Bordeaux mixture at 3 000 g/ha, between the stage of closing of the cluster and the post-veraison, is sufficient to significantly reduce the content in 4-mercapto-4-methylpentan-2-one (4-MMP), a main component of the characteristic Sauvignon wines aroma. Increase of the introduced copper quantities in the must as well as of the number of applications, results in a greater reduction of the content in this thiol, as 4-MMP reacts with copper residues during alcoholic fermentation while its precursor is revealed into an aroma. Nevertheless, the experiments with a polymer that eliminates copper from the juice prior to alcoholic fermentation, showing in some cases no recovery in the wines 4-MMP content, lead us to the hypothesis that copper might as well intervene during ripening of the grapes, causing thus a limitation of the aroma's precursor synthesis. By the sensory analysis, Sauvignon wines produced from copper treated vines showed much less characteristic aroma than those produced from not treated vines (having nevertheless been protected by an organic fungicide) and were lower graded. While the average grade for the last ones was 7,9/10, this grade was lowered to 2,9/10 and to 2,8/10 for the samples produced after one and two or three vine's copper treatments respectively. Grapes sugar concentration can also be affected by the vine's cupric treatments. Throughout the 3-year study, differences in sugar concentration up to 40 g/l have been observed, especially concerning the treatments made between stages of closing of the cluster and veraison. Nevertheless, sugar content seems highly dependent on the number of cupric applications, the period of their application as well as climatic conditions during vine sprayings.

Several yeast strains of the species S. cerevisiae, S. bayanus and S. paradoxus, first identified by hybridization experiments and DNA/DNA hybridization were characterized by using Polymerase Chain Reaction/Restriction Fragment Length Polymorphism (PCR/RFLP) of the MET2 gene. The concordance between this tool and classical genetic analyses did not reveal any exception for all the strains analysed, so PCR/RFLP of the MET2 gene proves to be a reliable and fast tool for delimiting S. cerevisiae and S. bayanus. OEnological strains race bayanus, chevalieri, capensis gave S. cerevisiae restriction patterns, whereas most of strains race S. uvarum belong to S. bayanus and displayed a specific chromosomal band patterns different from band patterns of S. cerevisiae strains. To avoid confusion in oenological terminology, oenologists should no longer use the name of bayanus to designate industrial or wild S. cerevisiae Gal- strains, and should consider S. bayanus as a distinct species.

4-mercapto-4-methylpentan-2-one (4MMP), a powerful aromatic component from Sauvignon variety, is present at trace levels in the wines from this cultivar. A method is proposed ta measure the amount of 4MMP in Sauvignon wines. It combines the extraction of wines volatile constituents using a dynarnic headspace technique and the selective reaction between thiols and p-hydroxymercuribenzoatc (pHMB). This combination is reversible in presence of an excess of cystein or glutathione. Finally, the organic extract is injected on agas chromatograph coupled with a flame photometric detector. Using this method, 4MMP content in Sauvignon wines can be determined with good repetability and sensitivity. These results enable us to evalue the incidence of viticultural and oenological aspects on the level of this aromatic component in Sauvignon wines.

4-mercapto-4-methylpentan-2-one (4-MMP), a strongly odorant compound responsible for the « boxtree » or « broom plant » odour of the Sauvignon wines, can be enzymaticaly released in vitro from an odourless must extract. The enzyme source used is a cell-free extract of the gastrointestinal bacterium Eubacterium limosum. This crude preparation exhibits a cysteine β-lyase activity which requires the presence of pyridoxal phosphate. The release of 4-MMP is inhibited when the substrate is previously treated with N-hydroxysuccimide acetate which reacts with a primary amine. The same bacterial extract is also able to release 4-MMP, pyruvic acid and ammonium, from S-(4-méthylpentan-2-one)-L-cysteine. On the other hand, the cleavage of S-(4-méthylpentan-2-one)D,L-homocysteine and S-(4-méthylpentan-2-one)- glutathione is very limited. These results suggest that the precursor of 4-MMP in Sauvignon must is a S-cysteine conjugate. Such an aroma precursor in grapes or in other fruits has never been round berore.

Pendant le séchage naturel à l'air libre du bois de chêne, on assiste à une diminution régulière de la teneur du bois en composés extractibles et notamment en composés phénoliques du type ellagitanins. La diminution de la teneur en ellagitanins provient essentiellement de la disparition des formes oligomères solubles dans l'eau; les tanins polymérisés non extractibles car liés aux parois, évoluent peu au çours du séchage naturel à l'air libre. Les bois séchés rapidement à l'étuve possèdent toujours des quantités plus importantes de polyphénols. Dans le même temps et quel que soit le mode de séchage, on obselVe une diminution des coumarines glucosilées et une augmentation non proportionnelle des formes aglycones. D'un point de vue organoleptique, la diminution de l'ensemble des polyphénols pendant le séchage peut être interprétée comme favorable à l'évolution de la qualité du merrain. En effet, les fractions amères et astringentes du bois de chêne correspondent respectivement .sr certains tanins ellagiques et catéchiques. L'intelVention des micro-organismes isolés de bois de chêne en cours de séchage naturel dans la disparition des composés phénoliques du bois est discutée. La grande majorité des moisissures étudiées est capable de dégrader enzymatiquement les tanins hydrolysables du chêne. Cependant, ces mêmes composés s'hydrolysent et s'oxydent spontanément en présence d'eau et d'oxygène. En conséquence, considérant le profil de colonisation du bois par les micro-organismes et celui des composés phénoliques extractibles, on peut supposer que l'on assiste vraisemblablement pendant le séchage naturel du bois à une dégradation biochimique et chimique des polyphénols dans les couches superficielles du merrain (0 à 4 mm de profondeur) et à une dégradation presque' exclusivement chimique au coeur du merrain. La présence d'eau et d'oxygène apparaÎt par conséquent comme un facteur important dans l'évolution de la composition du bois pendant son séchage.

Pendant le séchage des merrains sur parc à l'air libre, on assiste à une profonde modification de la composition chimique et du profil aromatique du bois de chêne. La teneur en eugénol, en aldéhydes phénols et en Β-méthyl-y-octalactone augmente régulièrement pendant le vieillissement du bois. Principalement sous forme trans au début du séchage, la Β-méthyl-y-octalactone s'accumule finalement sous la forme cis plus aromatique. Dans le même temps, on observe également une accumulation importante du précurseur inodore de Β-méthyl-y-octalactone. L'intervention des micro-organismes fréquemment isolés sur le bois en cours de séchage naturel sur la formation de composés aromatiques a été étudiée. La culture de diverses moisissures isolées de bois en cours de séchage naturel sur extraits de bois et directement sur sciure de chêne aboutit dans tous les cas à une forte diminution des teneurs en aldéhydes phénols, notamment de la vanilline. En effet, tous les micro-organismes étudiés (Penicilium sp., Trichoderma sp., Aureobasidium sp.) sont incapables de dégrader la lignine car ils ne possèdent pas d'activité ligninase. En revanche, ces champignons possèdent une forte activité oxydo-réductase capable de réduire la vanilline en alcool vanillique inodore. En conséquence, les aldéhydes phénols apparaissant au cours du séchage naturel du merrain ne dérivent pas d'une attaque enzymatique mais plus vraisemblablementde l'acidolyse et de l'oxydation chimique de la lignine du bois. Le stockage du bois à l'air libre en présence d'eau et d'oxygène doit permettre une évolution favorable de son potentiel aromatique tant que la vanilline et la cis Β-méthyly-octalactone s'accumulent.

Pendant le séchage naturel et le vieillissement à l'air libre du bois de chêne débité en merrain, on assiste à l'envahissement progressif du bois par différents micro-organismes. On a identifié dans ce travail 19 genres et 27 espèces de champignons, 2 genres et au moins 4 espèces de bactéries. La très grande majorité des micro-organismes est localisée dans les couches superficielles du bois. Seuls certains champignons sont retrouvés au coeur du merrain ayant vieilli 5 ans et plus sur parc. La déshydratation rapide du bois semble limiter le développement et l'envahissement en profondeur par les moisissures. Un champignon basidiomycète à arthroconidies, non formellement identifié, qui produit une pourriture blanche, a été isolé dans des merrains stockés 10 ans à l'air libre. Excepté ce champignon particulier, qui grâce à un équipement enzymatique adapté est susceptible d'attaquer simultanément tous les constituants pariétaux, les autres micro-organismes identifiés sont essentiellement cellulolytiques et ne peuvent pas altérer profondément la composition ni la structure du bois. En revanche, ils devraient pouvoir augmenter notablement la perméabilité et l'accessiblité aux liquides des couches superficielles du merrain et faciliter l'implantation ultérieure de basidiomycètes lignolytiques.

Les goûts et odeurs à caractère "moisI" retrouvés dans les vins encore stockés en cuves ou en barriques sont généralement dus à des chloroanisoles du type 2,3,4,6-tétrachloroanisoleet pentachloroanisole. Ces composés malodorants proviennent de la dégradation microbienne de chlorophénols utilisés comme traitement insecticide de différents matériaux à base de bois principalement employés dans la construction des bâtiments, leur isolation ou dans la fabrication de caisses de stockage des bouteilles. Dans certaines conditions, humidité de l'air élevée et ventilation réduite, on assiste à une contamination rapide de l'atmosphère des caves et des vins qui y sont entreposés. De la même façon, la conservation dans une atmosphère viciée de certains produits destinés à entrer en contact avec le vin peut être responsable de sa pollution. L'élimination de la source de contamination en chlorophénols et en chloroanisoles, ainsi que l'amélioration du renouvellement de l'air, suffisent généralement à solutionner le problème. La prohibition de tous les produits de traitements à base de chlorophénols est conseillée dans tous les locaux destinés à recevoir du vin en vrac où à le conditionner en bouteille. La cuverie contaminée en même temps que les vins peut être réutilisée après nettoyage et éventuellement réfection. A l'inverse, les contenants en bois conservés dans une atmosphère polluée doivent le plus souvent être éliminés.

Une nouvelle technique de la biologie moléculaire, la réaction de polymérisation en chaine (PCR) permet l'identification des souches de levures de vinification. Mise en oeuvre directement sur levures entières, elle permet d'obtenir des profils variables selon les souches, par l'amplification de séquences d'ADN génomique. Utilisée sur lies, la PCR constitue un outil rapide et sensible pour le contrôle d'implantation des levains en vinification. Cependant le pouvoir discriminant de la PCR est inférieur à celui de l'électrophorèse en champ pulsé pour la caractérisation des souches de levures indigènes. Elle doit être considérée comme une technique complémentaire d'identification des souches de S. cerevisiae.

L'élevage des vins rouges en barriques peut présenter certains risques microbiologiques lorsqu'il n'est pas correctement maÎtrisé. L'augmentation de la teneur du vin en acide acétique liée au développement de bactéries acétiques aérobies est facilement inhibée par le respect de règles élémentaires. En revanche, l'hydrolyse des groupements acétyles des hémicelluloses du bois de chêne conduit systématiquement à une faible augmentation de l'acidité volatile des vins conservés en barriques neuves. Ce phénomène devient négligeable avec le bois usagé lorsque l'élevage est bien contrôlé. Le développement de levures de contamination du genre Brettanomyces/Dekkera, produisant des teneurs élevées en éthyl-phénols entre le début de l'été et la fin de l'automne, est plus difficile à maÎtriser. Seul le maintien d'une teneur suffisante en anhydride sulfureux tout au long de leur élevage permet d'empêcher la multiplication de ces micro-organismes dans les vins rouges. En plus de la dose, les conditions de sulfitage des vins et des barriques sont également importantes. L'apport d'une quantité de SO2 non inférieure à 7 g par fût sous forme gazeuse dans un fût vide permet simultanément la désinfection des douelles et le sulfitage des vins. A dosage identique, avec un sulfitage direct du vin, le développement de Brettanomyces intermedius n'est pas inhibé et les vins risquent de présenter un caractère phénolé désagréable en fin d'élevage. Par ailleurs, les sulfitages à la mèche ou à la pastille ne possèdent pas la même efficacité. Si à quantité de soufre identique le méchage à la pastille procure un sulfitage presque deux fois plus important, selon l'origine et les méthodes de fabrication employées, les pastilles de soufre possèdent une stabilité au vieillissement variable se traduisant par des sulfitages irréguliers en fonction de leur âge et de leurs conditions de stockage. La présence d'une charge non combustible hygroscopique entrant dans la composition de certaines pastilles de soufre est responsable de cette instabilité.

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.

Les protéines ou glycoprotéines de poids moléculaire compris entre 20.000 et 35.000 Da sont responsables de la casse protéique des vins blancs. Leur séparation par électrophorèse capillaire permet de montrer que ce sont les fractions protéiques les moins thermostables qui sont les plus difficiles à éliminer par la bentonite. D'autre part, il est montré que, lors de l'élevage sur lies des vins blancs, on assiste à une amélioration de la stabilité protéique. Cette amélioration n'est pas dûe à une activité protéolytique des levures au cours de leur autolyse puisque les teneurs en protéines varient peu et que l'addition d'un autolysat à activité protéolytique a peu d'effet sur la stabilité protéique. En fait, l'amélioration de la stabilité protéique des vins blancs au cours de l'élevage sur lies apparaÎt essentiellement due à l'effet protecteur de macromolécules libérées à partir des parois levuriennes. En effet, l'addition de mannoprotéines à un vin permet d'augmenter sa stabilité protéique et par la même de diminuer la dose de bentonite nécessaire à sa stabilisation.

L'emploi de certaines préparations pectolytiques sur moût peut conduire à une teneur en vinyl-phénols élevée à l'origine d'odeurs et de goûts indésirables dans les vins blancs. Nous montrons dans ce travail que de nombreuses préparations enzymatiques issus de Aspergillus niger contiennent une activité du type cinnamyl-estérase (CE) capable d'hydrolyser les esters tartriques des acides hydroxycinnamiques du moût au cours de la phase pré-fermentaire, en libérant des acides trans p-coumarique et férulique. Sous l'action de l'activité cinnamate-décarboxylase (CD) de Saccharomyces cerevisae, ces acides phénols sont transformés en vinyl-phénols correspondants au cours de la fermentation alcoolique (vinyl-4-phénol et vinyl-4-gaïacol). Le choix d'une souche de levure à faible activité CD (ZYMAFLORE VL 1) permet d'éviter l'apparition d'un caractère phénolé désagréable. Par rapport à une préparation commerciale brute, l'utilisation d'une préparation expérimentale à faible activité CE (NOVO NORDISK FERMENT Ltd) limite très significativement la synthèse de vinyl-phénols des vins sans affecter le potentiel clarifiant de la préparation enzymatique.

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.

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.

L'analyse des caryotypes par électrophorèse en champs pulsés permet l'étude de l'écologie des souches de Saccharomyces cerevisiae dans le cas de levurage avec des levures sèches actives, au cours de la vinification des vins rouges. Les résultats obtenus montrent que le levurage de certaines cuves modifie la microflore des cuves non levurées de la cave. De même, le levurage dans un chai avec des souches de levures différentes permet d'obtenir l'implantation souhaitée.

Les auteurs étudient les glycoprotéines dans des moûts de raisins blancs. Ces glycoprotéines sont fractionnées par chromatofocalisation et caractérisées par différentes techniques séparatives : CLHP, électrophorèse, SDS-PAGE, analyse des acides aminés, analyse des oses. Un traitement à la bentonite et un test à la chaleur d'un moût de Sauvignon mettent en évidence qu'une fraction sur les 7 isolées est plus facilement adsorbée par la bentonite et que seulement 3 fractions sur les 7 ont une aptitude à provoquer un trouble après chauffage. La teneur en glycoprotéines varie en fonction du cépage, du degré de maturité de la vendange et des modalités préfermentaires (sulfitage, pressurage et macération).

La composition colloïdale des moûts, c'est-à-dire les macromolécules solubles et les « bourbes fines », joue un rôle déterminant sur le développement et le terme de la fermentation alcoolique en vinification en blanc sec. La fixation des acides gras par les « bourbes fines » permet l'interprétation partielle du phénomène. Ces résultants montrent qu'il conviendrait, dans la pratique, d'accorder une plus grande attention à la turbidité des moûts débourbés ainsi qu'à leur teneur en macromolécules. +++ Must colloïdal composition, ie soluble macromolecules and « racking light sediments » play an important role on the development and the finishing fermentation in white wine vinification. The fatty acids fixed on the « racking light sediments » allow to explain partially this phenomenon. These results show that it would be convenient, in practical conditions, to pay a greater attention on the turbidity of racked musts and on their macromolecule contents.

Les difficultés de filtration constituent un obstacle important pour la clarification et la stabilisation de certains vins. Le millésime 1974 a apporté de nombreux exemples de filtrations difficiles, particulièrement dans les vins blancs liquoreux issus de vendanges botrytisées, mais aussi dans certains vins blancs secs et dans certains vins rouges. On peut supposer que l'effet mécanique des grandes rotations sur la structure colloïdale du vin est responsable de cette amélioration de la filtration. En partant de cette observation, nous avons cherché la possibilité d'obtenir une amélioration encore plus sensible des débits de filtration et des volumes filtrés avant colmatage des surfaces filtrantes, en faisant intervenir une action mécanique plus importante à l'aide d'un dispositif d'ultradispersion. (*) Ce travail a été effectué avec l'aide matérielle du Conseil Interprofessionnel du Vin de Bordeaux.

La nature du cépage, l'état sanitaire et surtout les traitements mécaniques des raisins commandent la clarification du moût; les modalités de débourbage statique interviennent peu. Pour un niveau de clarification identique, un moût provenant d'une vendange foulée énergiquement fermente moins bien que le même moût extrait par pressurage sans foulage. Cette incidence des matériels sur les processus fermentaires constitue un fait nouveau dont il faudra tenir compte dans l'équipement des chais. +++ The grape variety, soundness, and especially its mechanical processing are factors in juice clarity; the type of static settling has little effect. For an identical clarification level, a juice obtained from an energetically crushed harvest does not ferment as well as the same juice extracted by pressure without crushing. The fact that fermentation processes are affected by the machinery used is new, and must be taken into account when equiping wineries.

Les polysaccharides solubles du jus de raisin sont dosés par les méthodes au phénol et au carbazol sulfuriques. Au cours de la maturation, la teneur en pectine soluble passe par un maximum, puis décroît. L'incidence de ces transformations sur les opérations préfermentaires de la vinification en blanc (pressurage et débourbage) est examinée. +++ Soluble polysaccharides from grape juices are estimated with phenol-and carbazol-sulfuric methods. During the ripening, the soluble pectin content waches a maximum then decreases until maturity. The effect of these changes on the first steps of the white wine making (juice extraction and static settling) are examined.

A l'issue du débourbage statique, des essais de filtration des dépôts bourbeux d'une part, du moût clair soutiré d'autre part, ont été réalisés. L'incidence de ces traitements sur la fermentescibilité des moûts et la formation de substances volatiles par la levure a été examinée. +++ After static settling, filtration tests were carried out on both the sediment and the clear must drawn off. The effect of these treatments on the fermentability of the musts on the formation of volatile compounds by yeast was examined.

L'analyse des profils de restriction de l'ADN mitochondrial des levures permet une caractérisation fine des souches de Saccharomyces cerevisiae. Cette analyse a été appliquée à deux souches de levures sèches actives et à une vingtaine de souches indigènes, isolées de différents moûts lors de la fermentation spontanée. Les profils de restriction de l'ADN mt des souches étudiées présentent une grande diversité. La méthode mise en oeuvre est décrite de façon détaillée et les applications pratiques discutées. +++ The analysis of restriction patterns from yeast's mitochondrial DNA leads to a fine characterization of different strains of Saccharomyces cerevisiae. This analysis has been applied to two commercial strains and to twenty wild yeasts, isolated from different musts in case of natural fermentations. The DNA restriction patterns of the strains studied present a wide diversity. The method we used is minutely described and the practical applications are discussed.

Nous proposons dans cette note une méthode originale de dosage simultané des polysaccharides et des protéines des moûts et des vins, par chromatographie liquide haute pression de tamisage moléculaire. L'application de la chromatographie liquide haute pression pour le dosage global des protéines solubles des moûts et des vins a déjà été signalé par P.-J. TYSON (1981) qui opère par chromatographie d'exclusion.

Les auteurs étudient la clarification des bourbes de moûts blancs avec un filtre presse équipé de plateaux à membrane. L'addition d'un adjuvant sous forme de perlite (BECOLITE 5000, perméabilité 2,100 Darcy) à la dose de 1.500 g par hectolitre permet d'atteindre des débits moyens suffisants, de l'ordre de 120 à 150 litres par heure et par m2 pour des cycles de filtration de 90 minutes. La qualité de la clarification est satisfaisante. A cet égard, le filtre presse se montre plus performant que la centrifugation. Les jus bourbeux ainsi clarifiés peuvent être réincorporés dans le moût débourbé statiquement. La dégustation ne permet pas de distinguer les vins issus de moût additionné ou non de leurs dépôts bourbeux clarifiés (par filtration ou centrifugation).

La mesure de l'activité laccase (E.C. 1.10.3.2.) de jus de raisins par la méthode à la syringaldazine (DUBOURDIEU et al., 1984) permet d'apprécier la contamination de la vendange par Botrytis cinerea. Nous précisons et améliorons cette technique de dosage pour l'appliquer au contrôle rapide de l'état sanitaire des moûts et des vins nouveaux.

Botrytis cinerea secrète dans les baies de raisins parasitées un β-glucane responsable des difficultés de clarification des vins issus de vendanges pourries. Une préparation enzymatique (glucanase NOVOZYM 116) susceptible d'hydrolyser ce polysaccharide dans les vins est proposée. L'incidence de différents facteurs (température, pH, SO2, éthanol) sur l'activité et la stabilité de la préparation enzymatique, ainsi que son mode d'action, sont examinés. Les essais effectués au laboratoire montrent que la dégradation enzymatique du glucane, en cours de fermentation, permet d'améliorer considérablement la clarification spontanée et la filtrabilité des vins. +++ Botrytis cinerea secretes a β-glucane in the grapes that it infests that is responsible for clarification problems in wines made from spoiled harvests. An enzymatic preparation (Glucanase NOVOZYM 116) capable of hydrolysing this polysaccharide in wines is proposed. The influence of different factors (temperature, pH, SO2, ethanol) on the activity and stability of the enzymatic preparation are examined. The laboratory tests show that the enzymatic decay of glucane during fermentation brings about a great improvement in the spontaneous clarification and filterabiiity of wines.