Enological Techniques Research Articles

Copigmentation evidence of phenolic compound: The effect of caffeic and rosmarinic acids addition on the chromatic quality and phenolic composition of Cabernet Sauvignon red wine from the Hexi Corridor region (China)

Although phenolic copigments are rarely colored, they can still influence color expression in red wine copigmentation. Here, prefermentative agents, such as caffeic and rosmarinic acids, were added as copigments during Cabernet Sauvignon red winemaking. The evolution of colors and polyphenols was analyzed by tristimulus colorimetry and high-performance liquid chromatography-tandem mass spectrometry during brewing and aging periods. The results showed that the addition of caffeic and rosmarinic copigments was beneficial to obtain more saturated and vivid hue of wines. The changes in color were correlated with a significant increase in anthocyanins concentration. Moreover, the results demonstrated that the addition of the two phenolic copigments increased the concentration of total phenols and enhanced the copigmentation effect, indicating improved chromatic intensity and color stability of wines. Therefore, the addition of caffeic and rosmarinic acids is a simple and useful enological technique to obtain red wines with high color quality and aging potential.

Key facts about rotundone and practical ways to pepper your wine with this fascinating aroma compound

In 2008, the sesquiterpene rotundone was identified as the main contributor to the aroma of black pepper in wine. Since then, this potent aroma compound has been detected in several grape varieties. In most cases, rotundone is positively perceived by consumers. One of the most fascinating fact about this molecule is probably that 20 to 25 % of the general population is anosmic to it. This technical review provides key facts about rotundone and practical ways to manipulate its concentration in wine using enological and viticultural techniques.

May peppery wines be the spice of life? A review of research on the ‘pepper’ aroma and the sesquiterpenoid rotundone

Rotundone is the main aroma compound responsible for peppery notes in wines. Since its discovery in 2008, this potent and fascinating odorant has been the subject of many research studies worldwide. The aim of this review is to summarize these works. Rotundone is a rather ubiquitous molecule that has been detected in many grape varieties. As with other sesquiterpenes, the proposed biosynthetic scheme for rotundone involves both the methylerythritol phosphate (MEP) and the mevalonate (MVA) pathways. The production of the compound by the plant, which could be a response to biotic stress, is also affected by abiotic factors. In most cases, studies showed that rotundone was neutrally or positively perceived by consumers, which makes the peppery note a desirable character in vine. Practical ways were identified to modulate rotundone levels in wines using viticultural and enological techniques. Climate change, through the expected alteration of precipitation regime and a rise in temperature over the grape maturation period, should have a depreciative impact on rotundone accumulation. Adaptation strategies in this context, together with other perspectives of research, are discussed in concluding this review.

Removal of Copper from White Wine: Imidazole-Based Polymers Are Efficient at Copper Adsorption

Summary Goals: Spray management in the vineyard and enological techniques for mitigating sulfur off-odors may lead to detectable accumulation of copper (Cu) in wine. Although widely used in winemaking, this transition metal may be detrimental to wine aromatics postbottling, has legal limits in many countries, and may be a health hazard if consumed in enough quantity. Cu concentration is therefore monitored, and, when necessary, reduced. To assess the efficacy of commercially available products at removing Cu from wine, a selection of both traditional and novel fining agents were tested. Key Findings: Of the seven fining products used, those comprising a polyvinyl imidazole and polyvinylpyrrolidone copolymer (PVI-PVP) were most effective in reducing Cu concentrations, removing up to 94% of added Cu after 72 hrs. Agents composed of yeast, potato protein, and bentonite showed little capacity for removing added Cu from wine. Impact and Significance: Winemakers in past decades have relied on various methods to reduce Cu concentrations in wine; among these is a treatment known as “blue fining”, a procedure requiring ferrocyanide that can generate a toxic by-product. Alternative methods yielded substantial reduction in added Cu(II) from white wine with PVI-PVP-containing fining agents. These agents represent promising and safe alternative methods of Cu removal. The addition of PVI-PVP agents following Cu treatments of wines may be the most practical method for reducing Cu concentrations, and will subsequently inhibit postbottling formation of hydrogen sulfide and prevent possible illnesses associated with Cu consumption.

Impact of Adding Ellagic Acid to Red Grapes on the Phenolic Composition and Chromatic Quality of Cabernet Sauvignon Wines from a Warm Climate

In this study, the effect of adding ellagic acid (Ea) before alcoholic fermentation on the phenolic composition and chromatic quality of Cabernet Sauvignon wines were investigated. The evolution of the color and polyphenolics was determined by tristimulus colorimetry and HPLC-MS during the industrial-scale winemaking process, which showed that the prefermentation addition of Ea could obtain more saturated and vivid hue wines, consistent with the significant increase in anthocyanins concentration. The copigmentation effect induced by Ea was also confirmed by the higher copigmentation degree in the treated samples. Thus, the addition of Ea could provide a simple and useful enological technique to enhance the red wine quality, improve the intensity and stability of wine color, and can be employed as an alternative strategy for obtaining high-quality red wines from a warm climate region (e.g., Xinjiang Uygur Autonomous Region, northwest China). Practical Application The main objective of this work is to evaluate the effect of adding Ea before alcoholic fermentation on color and phenolic compounds of red wines, which could be helpful in reasonably application of copigment additives and enlargement the understanding of the chemistry of interaction between this copigment and anthocyanins. Although the Ea is currently not approved for use in wines in somewhere of world, this addition treatment could provide a useful enological technique to enhance the intensity and stability of red wine color. For this reason, we believe that this study is valuable in providing useful insights for future research.

Cell wall compounds of red grapes skins and their grape marcs from three different winemaking techniques

Different winemaking practices are aimed at increasing cell wall degradation to facilitate extraction of valuables molecules into the wine. However, little attention has been paid to the composition of marcs from different cultivars according to the influence of the winemaking procedures. We provide information on skin cell walls from Cabernet Sauvignon, Syrah and Monastrell grapes and examine how different winemaking practices (addition of enzymatic preparation and β-galactosidase separately and dry ice addition) may affect the composition of marc skin cell wall material (CWM). The efficiency of CWM isolation from the grape skin and also its composition is influenced by the cultivar. A similar cultivar influence has been detected on CWM from the marc, being the differences also due to the enological technique. Our results help to increase our knowledge on the degradation of cell walls during vinification, while providing a valuable guideline to upgrade the value of these by-products.

Effect of SO2, reduced glutathione and ellagitannins on the shelf life of bottled white wines

This work studied the effect of reduced glutathione (GSH) and/or ellagitannins added at bottling on the shelf life of a white wine with a medium/low SO2 content at two levels (−SO2 and +SO2). After 3 months of bottle aging, the trials with the higher level of SO2 (+SO2) were significantly less colored, more fruity, more soft and less bitter than the corresponding trials with the lower level of SO2 (−SO2). After 6 months, the +SO2 trials were significantly distinguished from the −SO2 trials for the more intense floral and fruity notes and the less intense oxidative notes. The addition of GSH and/or ellagitannins did not extend the shelf life of bottled wines: no complementary effects of these additives to SO2 were observed. The effect of GSH was also studied at higher levels of SO2 and two different levels of dissolved oxygen. The addition of GSH caused a significant increase in the oxygen consumption rate during the first month of bottle aging, but after 1 year, no effects on the oxidation process were observed. GSH, unlike other antioxidant additives, did not increase the consumption of SO2. GSH, like SO2, can most likely react with o-quinones but, most likely, not with the hydroperoxyl radical to yield hydrogen peroxide, which causes an increase in SO2 consumption. The rapid and almost complete loss of GSH was observed during the first months of bottle aging. The possibility of using doses of GSH > 20 mg L−1 and combining enological techniques aimed at controlling the multiple causes of wine oxidation should be taken into account.

The composition of cell walls from grape marcs is affected by grape origin and enological technique

The grape marc obtained after vinification could be a source of high value compounds and the different winemaking techniques could influence such compounds. The composition of skin cell walls from Monastrell grapes grown in three different locations near Murcia (S.E. Spain) has been studied. The grapes were winemaked with three different techniques (cold pre-fermentative maceration, β-galactosidase enzyme addition and enzymatic preparation addition) and the marc skin cell walls were studied to determine their composition. The results suggest that terroir influenced the percentage of grape skin, the amount of cell wall material isolated from the grape skin, the carbohydrate composition of the cell wall material, and the lignin and protein content of the cell wall material from grape skin. A similar trend has been found within the influence of terroir on cell wall material isolated from the skin separated from the marc, being the differences also due to the enological technique.

Factors influencing the aroma composition of Chardonnay wines.

Chardonnay is one of the oldest and most widely distributed wine grape cultivars and is of commercial importance for the world's wine-producing nations. It is an extremely flexible variety that has adapted to different regions with varied weather and soil characteristics. Somewhat uniquely among white wines, Chardonnay lends itself to a wide variety of production styles, which can be tailored to the target market. Techniques such as skin maceration, barrel and stainless steel fermentation, use of selected or indigenous yeasts, malolactic fermentation, and aging in barrels with or without lees are all applicable and lead to different compositional outcomes. A number of research papers have been published with a view to understanding Chardonnay composition and quality as well as the impact of different enological techniques on the final product. This review summarizes current knowledge, explaining the influence of viticultural and production techniques on aroma composition, and poses directions for further research into Chardonnay wines.

Aging of red wines made from hybrid grape cv. BRS Violeta: Effects of accelerated aging conditions on phenolic composition, color and antioxidant activity

Aging is an enological technique usually employed with Vitis vinifera wines for improving and stabilizing wine sensory attributes like red wine color. However, red wines made from non-vinifera grape cultivars are considered not suitable for classic wine aging because they are prone to color loss during processing and storage, mainly due to the major occurrence of non-acylated anthocyanidin 3,5-diglucosides. The recently developed hybrid grape cv. BRS Violeta gives rise to deep red-purplish colored wines characterized by an important contribution of p-coumaroylated anthocyanidin 3,5-diglucosides. In this work, Violeta red wines were subjected to control (storage at 15°C) and accelerated (storage at 25, 35 and 50°C) aging for 120days. Total phenolic content was only significantly decreased by 23% in accelerated aged wines at 50°C, whereas antioxidant capacity was mainly reduced in the first 20days of aging (around 35% for all the wines, except for 45% for wine aged at 50°C) and then remained almost stable. In contrast, total anthocyanin content decreased following expected first-order kinetics and the variation of rate constants with regard to temperature fitted well with an Arrhenius-type equation. The calculated activation energy for disappearance of anthocyanins (47kJ/mol) was close to the lower limit of the range of values reported for thermal degradation of anthocyanidin 3-glucosides. In addition, half-life values for p-coumaroylated anthocyanidin 3,5-glucosides of Violeta wine aged at 50°C almost doubled those of their corresponding non-acylated derivatives. The latter result is suggested to be the main reason behind the relatively high resistance of Violeta wine towards the disappearance of anthocyanin under accelerated aging conditions. Finally, chromatic characteristics of Violeta wines did not significantly change their C* values during aging but L* and h* values increased as expected, the latter mainly due to higher increases of the yellow color component (b*) over lower decreases of the red color component (a*). These color changes were more drastic in the accelerated aged wines and the wine aged at 25°C still maintained interesting color characteristics close to those of the control aged wine that did not change very much.

Effect of co-winemaking in phenolic composition, color and antioxidant capacity of young red wines from La Mancha region

The influence of co-winemaking technique on the phenolic profiles, color and antioxidant capacity of wines made from red grape varieties cultivated in La Mancha region (Spain) was investigated. Co-winemaking red wines were obtained by pre-fermentative blend of grapes (1:1, w/w) from the predominant Cencibel (Tempranillo) variety in this region and the minor varieties Bobal, Moravia Agria, Moravia Dulce, Tortosi and Rojal, together with a three varieties blend (1:1:1, w/w/w) of Cencibel, Bobal and Moravia Agria grapes. The phenolic profiles obtained in co-winemaking wines showed more quantity of different compounds than single-variety wine of Cencibel used as reference. The best results were obtained using Bobal, Moravia Agria and Moravia Dulce varieties for co-winemaking, especially an improvement of color characteristics. All co-winemaking wines significantly increased the total resveratrol content as compared to the Cencibel reference wine, although cis-isomers largely predominated in all wines. Moravia Agria and Rojal varieties produced co-winemaking wines with decreased antioxidant capacity, whereas Bobal and Moravia Dulce varieties increased it, even when the co-winemaking wine from Moravia Dulce contained less total polyphenols than Cencibel reference wine. Co-winemaking technique can be suggested as a way to widen the offer of wines to consumers, incorporating characteristic properties of minor grape varieties. In addition, this enological technique has the benefit of avoiding the disappearance of native species, thus improving the biodiversity of La Mancha region.

The Extraction of Anthocyanins and Proanthocyanidins from Grapes to Wine during Fermentative Maceration Is Affected by the Enological Technique

The effect of three enological techniques (low temperature prefermentative maceration, must freezing with dry ice, and the use of a maceration enzyme) on the extraction of anthocyanins and proanthocyanidins from must to wine during fermentative maceration was studied to determine the extent to which these compounds are extracted and to assess the changes on their qualitative composition due to enological technique applied. The results showed that the dry ice treatment led to wines with high color intensity and high anthocyanin content, the maximum rate of extraction being observed the first 6 days of fermentative maceration. Regarding the effect of the different techniques on the quantitative and qualitative composition of proanthocyanidins, only the dry ice treatment seemed to favor the extraction of high molecular weight skin proanthocyanidins. The low temperature prefermentative maceration treatment led to the highest concentration of proanthocyanidins at the moment of pressing; however, this treatment, contrary to expectations, led to wines with the highest content of seed-derived proanthocyanidins. The use of the maceration enzyme also increased the concentration of proanthocyanidins during all of the fermentative process, as compared to a control wine, although the increase was not only due to skin proanthocyanidins but also seed proanthocyanidins. We have demonstrated in this study that maceration enzymes also facilitate seed phenolic extraction.

Improving headspace-solid-phase microextraction of 3-isobutyl-2-methoxypyrazine by experimental design with regard to stable isotope dilution gas chromatography?mass spectrometric analysis of wine

To solve problems of sensitivity, repeatability and multi-step extraction related to 3-isobutyl-2-methoxypyrazine (IBMP) determination in wines, a simple method based on the novel combination of solid-phase microextraction and stable isotope dilution assay is presented. Among the parameters that affect this type of extraction, five of them have been optimised since the other parameters have common values or do not require optimisation (e.g. addition of sodium chloride at saturated concentration) and so were fixed. Vial volume, sample volume/vial volume ratio, pH, adsorption time and temperature have been optimised by means of two experimental designs. After extraction, quantification was performed by stable isotope dilution with gas chromatography-tandem mass spectrometry ([2H2]-IBMP as internal standard). The final procedure allowed quantification far below IBMP’s sensory threshold (1 ng l−1 versus 15 ng l−1) with a 4% standard deviation. This method has been applied to experimental Fer servadou wines. Comparison of IBMP contents confirmed the efficiency of some viticultural and enological techniques on the herbaceous flavour decrease, such as prior fermentation maceration at high temperature (70 °C) and the use of a reflective carpet on viticultural soil.

Improving headspace-solid-phase microextraction of 3-isobutyl-2-methoxypyrazine by experimental design with regard to stable isotope dilution gas chromatography–mass spectrometric analysis of wine

To solve problems of sensitivity, repeatability and multi-step extraction related to 3-isobutyl-2-methoxypyrazine (IBMP) determination in wines, a simple method based on the novel combination of solid-phase microextraction and stable isotope dilution assay is presented. Among the parameters that affect this type of extraction, five of them have been optimised since the other parameters have common values or do not require optimisation (e.g. addition of sodium chloride at saturated concentration) and so were fixed. Vial volume, sample volume/vial volume ratio, pH, adsorption time and temperature have been optimised by means of two experimental designs. After extraction, quantification was performed by stable isotope dilution with gas chromatography-tandem mass spectrometry ([ 2 H 2 ]-IBMP as internal standard). The final procedure allowed quantification far below IBMP’s sensory threshold (1 ng l −1 versus 15 ng l −1) with a 4% standard deviation. This method has been applied to experimental Fer servadou wines. Comparison of IBMP contents confirmed the efficiency of some viticultural and enological techniques on the herbaceous flavour decrease, such as prior fermentation maceration at high temperature (70 °C) and the use of a reflective carpet on viticultural soil.

Concentrations of Selected Polyphenols in White Commercial Wines

Using an HPLC method with diode array detection, we have measured the concentrations of flavan 3-ols (catechin and epicatechin), trihydroxystilbenes (the <i>cis</i> and <i>trans</i> isomers of polydatin and resveratrol), flavonols (quercetin and rutin), and the hydroxy acid <i>p</i>-coumaric in 644 white wines from the major wine-producing regions. Quercetin and rutin were detectable in very few of these wines, and the latter could not be unequivocally distinguished from isoquercitrin, which was not specifically measured in this study. One or more of the hydroxystilbenes were measurable in most, but the <i>cis</i> isomers of polydatin and resveratrol were not frequently detectable. Among Chardonnay wines, those from Australia had the highest concentrations of both flavan 3-ols, while those from California were highest in <i>p</i>-coumaric acid and <i>trans</i>-resveratrol. For Sauvignon blanc wines, those of South Africa had the highest content of both flavan 3-ols. For Riesling wines, those from France (Alsace) were highest in (+)-catechin and <i>trans</i>-resveratrol, German wines in (-)-epicatechin, and Canadian wines in <i>trans</i>-polydatin. French wines from Pinot (blanc and gris) were higher in all constituents than North American, while Italian wines from this cultivar were the lowest. There were no significant differences in polyphenol concentrations between Gewürztraminer wines from France and North America. Low concentrations of polyphenols were found in miscellaneous white wines from Central Europe and Italy. When analyzed by cultivar rather than by region, highest flavan 3-ol concentrations were observed in wines from French hybrid grapes (Vidal blanc and Seyval blanc) and lowest in Gewürztraminer, whereas the former had lowest concentrations of <i>p</i>-coumaric acid and trihydroxystilbenes. In all instances, the concentrations of the polyphenols measured in white wines were 5% to 25% those of red wines (with quercetin and <i>cis</i>-trihydroxystilbenes being undetectable in most) and do not explain why white wines may have the same potency as red wines in certain biological functions. Climatic factors that appear to modulate polyphenol concentrations in red wines such as stress, fungal pressure and sunlight do not seem to be important for white wines. The intrinsic properties of the individual cultivars or clones together with regional differences in enological techniques may be the most important factors.

Metabolism ofSaccharomyces cerevisiaeFlor Yeasts During Fermentation and Biological Aging of Fino Sherry: By-products and Aroma Compounds

During the biological aging of the Fino sherry, the formation of aroma compounds takes place as a result of the oxidative metabolism of the <i>Saccharomyces cerevisiae</i> flor yeasts, which form a film on the surface of the wine. Yeasts consume some compounds such as ethanol, glycerol, organic acids (acetic, lactic, citric and succinic), and amino acids, including proline. At the same time, yeasts produce other compounds, namely higher alcohols (isobutanol and isoamilic), acetaldehyde and acetoin. We have compared differences in aroma production according to parameters involved in winemaking such as enological techniques applied, selected yeast strains used, and length of the aging process. Fermentation of must enriched in solids and other components resulted in fino sherry with a lower volatile acidity and a higher concentration of acetaldehyde, isoamilic alcohols, and glycerol than decanted must. Furthermore, while ethanol consumption was higher in "sobretablas", other compounds, such as acetic acid or glycerol, were steadily consumed throughout the aging period. As far as the strains are concerned, <i>S. cerevisiae (beticus)</i> and <i>S. cerevisiae (cheresiensis)</i> were better at reducing the volatile acidity than <i>S. cerevisiae ( montuliensis)</i>, which consumed more ethanol and produced more acetaldehyde (mainly responsible for the typical flavor of sherries). These results make it possible to select the final organoleptic characteristics of the wine by means of applying the appropriate enological processes and/or selected strain.

Wine as a biological fluid: History, production, and role in disease prevention

Wine has been part of human culture for 6,000 years, serving dietary and socioreligious functions. Its production takes place on every continent, and its chemical composition is profoundly influenced by enological techniques, the grape cultivar from which it originates, and climatic factors. In addition to ethanol, which in moderate consumption can reduce mortality from coronary heart disease by increasing high-density lipoprotein cholesterol and inhibiting platelet aggregation, wine (especially red wine) contains a range of polyphenols that have desirable biological properties. These include the phenolic acids (p-coumaric, cinnamic, caffeic, gentisic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin, epicatechin, and quercetin). They are synthesized by a common pathway from phenylalanine involving polyketide condensation reactions. Metabolic regulation is provided by competition between resveratrol synthase and chalcone synthase for a common precursor pool of acyl-CoA derivatives. Polymeric aggregation gives rise, in turn, to the viniferins (potent antifungal agents) and procyanidins (strong antioxidants that also inhibit platelet aggregation). The antioxidant effects of red wine and of its major polyphenols have been demonstrated in many experimental systems spanning the range from in vitro studies (human low-density lipoprotein, liposomes, macrophages, cultured cells) to investigations in healthy human subjects. Several of these compounds (notably catechin, quercetin, and resveratrol) promote nitric oxide production by vascular endothelium; inhibit the synthesis of thromboxane in platelets and leukotriene in neutrophils, modulate the synthesis and secretion of lipoproteins in whole animals and human cell lines, and arrest tumour growth as well as inhibit carcinogenesis in different experimental models. Target mechanisms to account for these effects include inhibition of phospholipase A2 and cyclo-oxygenase, inhibition of phosphodiesterase with increase in cyclic nucleotide concentrations, and inhibition of several protein kinases involved in cell signaling. Although their bioavailability remains to be fully established, red wine provides a more favourable milieu than fruits and vegetables, their other dietary source in humans. J. Clin. Lab. Anal. 11:287–313, 1997. © 1997 Wiley-Liss, Inc.

Wine as a biological fluid: History, production, and role in disease prevention

Wine has been part of human culture for 6,000 years, serving dietary and socio-religious functions. Its production takes place on every continent, and its chemical composition is profoundly influenced by enological techniques, the grape cultivar from which it originates, and climatic factors. In addition to ethanol, which in moderate consumption can reduce mortality from coronary heart disease by increasing high-density lipoprotein cholesterol and inhibiting platelet aggregation, wine (especially red wine) contains a range of polyphenols that have desirable biological properties. These include the phenolic acids (p-coumaric, cinnamic, caffeic, gentisic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin, epicatechin, and quercetin). They are synthesized by a common pathway from phenylalanine involving polyketide condensation reactions. Metabolic regulation is provided by competition between resveratrol synthase and chalcone synthase for a common precursor pool of acyl-CoA derivatives. Polymeric aggregation gives rise, in turn to the viniferins (potent antifungal agents) and procyanidins (strong antioxidants that also inhibit platelet aggregation). The antioxidant effects of red wine and of its major polyphenols have been demonstrated in many experimental systems spanning the range from in vitro studies (human low-density lipoprotein, liposomes, macrophages, cultured cells) to investigations in healthy human subjects. Several of these compounds (notably catechin, quercetin, and resveratrol) promote nitric oxide production by vascular endothelium; inhibit the synthesis of thromboxane in platelets and leukotriene in neutrophils, modulate the synthesis and secretion of lipoproteins in whole animals and human cell lines, and arrest tumour growth as well as inhibit carcinogenesis in different experimental models. Target mechanisms to account for these effects include inhibition of phospholipase A2 and cyclo-oxygenase, inhibition of phosphodiesterase with increase in cyclic nucleotide concentrations, and inhibition of several protein kinases involved in cell signalling. Although their bioavailability remains to be fully established, red wine provides a more favourable milieu than fruits and vegetables, their other dietary source in humans.

Resveratrol Glucosides are Important Components of Commercial Wines

Using a direct-injection HPLC method with isocratic elution and UV detection, the isomers of free resveratrol and their glucosides (polydatin) have been assayed in nearly 700 commercial red wines from most of the world9s areas of production. The highest concentrations of polydatin were found in wines from the Midi and Rhone Valley of France, Canada, Italy, Spain and Portugal, and South America. In the last three regions, the polydatin concentrations exceeded those of free resveratrol which were the lowest of all categories examined, suggesting that the high sugar content of warm climate grapes may favor the glycosylation of resveratrol. In nine regions, the concentration of <i>cis</i>-polydatin exceeded that of <i>trans</i>-polydatin, the reverse being the case in five, yet in all <i>trans</i>-resveratrol concentrations exceeded those of <i>cis</i>-resveratrol. There was only a weak negative correlation overall between polydatin and resveratrol concentrations when all wines were included in the analysis. The low values for both polydatin and resveratrol in Californian wines are consistent with the notion that, despite high sugar content, some grapes may fail to express resveratrol synthetic enzymes due to genetic characteristics or to lack of environmental stress, and consequently little of the free resveratrol is available for glycosylation. The influence of cultivar was examined in wines from several regions. Among wines from California, Australia, South America and Canada, highest polydatin concentrations were found respectively in those from Zinfandel, Shiraz, Merlot and Pinot noir. Wines from the Northern Rhone Valley (predominantly Shiraz) had lower concentrations than those from the Southern Rhone where Mourvedre, Grenache, Carignane and Cinsault predominate. The high polydatin and very low resveratrol concentrations of Vintage Ports highlight enological techniques, particularly duration of fermentation, as important modulating factors. The concentrations of polydatin present in most red wines are likely to add significantly to the presumed health benefits attributable to resveratrol.

Effect of several enological practices on the content of catechins and proanthocyanidins of red wines

Several microvinification experiments were conducted with Vranac red grapes to understand the effect of several enological techniques on the content of (+)-catechin, (-)-epicatechin, and procyanidin B-type dimers and trimer C-1 in wines, which were quantitated by HPLC. Both the length of maceration time and the presence of a high quantity of pomace, seeds, and stems in contact withthe must during fermentation led to wines with a higher content of catechins and proanthocyanidins