Wine Tannins Research Articles

Effect of Adding Seeds During Maceration on Quality of Wine From Vitis Vinifera CV. Cabernet Sauvignon

Red wines were made from Vitis vinifera cv. Cabernet Sauvignon in China at different methods of maceration. The effects of adding seeds during maceration on the quality characteristics, in terms of colour, aroma profile and sensory characteristics, of the wines before bottling were evaluated, and made a comparison with the effects of adding skins. Seed contact treatments raised wine colour intensity, proanthocyanidins, tannins, and polyphenols content in comparison to the control wines. However, as indicated in the sensory evolution, the significant increase in astringency intensity was found in the wines with seed contact. Besides, the bitterness of the red wine also increased in the wines with seed contact, but it was not significantly

Application of Insoluble Fibers in the Fining of Wine Phenolics

The application of animal-derived proteins as wine fining agents has been subject to increased regulation in recent years. As an alternative to protein-based fining agents, insoluble plant-derived fibers have the capacity to adsorb red wine tannins. Changes in red wine tannin were analyzed following application of fibers derived from apple and grape and protein-based fining agents. Other changes in wine composition, namely, color, monomeric phenolics, metals, and turbidity, were also determined. Wine tannin was maximally reduced by application of an apple pomace fiber and a grape pomace fiber (G4), removing 42 and 38%, respectively. Potassium caseinate maximally removed 19% of wine tannin, although applied at a lower dose. Fibers reduced anthocyanins, total phenolics, and wine color density, but changes in wine hue were minor. Proteins and apple fiber selectively removed high molecular mass phenolics, whereas grape fibers removed those of both high and low molecular mass. The results show that insoluble fibers may be considered as alternative fining agents for red wines.

HPLC Retention Thermodynamics of Grape and Wine Tannins

The effect of grape and wine tannin structure on retention thermodynamics under reversed-phase high-performance liquid chromatography conditions on a polystyrene divinylbenzene column was investigated. On the basis of retention response to temperature, an alternative retention factor was developed to approximate the combined temperature response of the complex, unresolvable tannin mixture. This alternative retention factor was based upon relative tannin peak areas separated by an abrupt change in solvent gradient. Using this alternative retention factor, retention thermodynamics were calculated. Van't Hoff relationships of the natural log of the alternative retention factor against temperature followed Kirchoff's relationship. An inverse quadratic equation was fit to the data, and from this the thermodynamic parameters for tannin retention were calculated. All tannin fractions exhibited exothermic, spontaneous interaction, with enthalpy-entropy compensation observed. Normalizing for tannin size, distinct tannin compositional effects on thermodynamic parameters were observed. The results of this study indicate that HPLC can be valuable for measuring the thermodynamics of tannin interaction with a hydrophobic surface and provides a potentially valuable alternative to calorimetry. Furthermore, the information gathered may provide insight into understanding red wine astringency quality.

A new approach to the analysis of tannin concentration using a microelectronic biosensor

Wine tannins are essential to the astringency and color stabilization of red wine through the formation of tannin conjugates. It is important to determine the concentration of tannins during wine aging and fermentation. The aim of this study was to establish a new method that allows for real-time analysis of tannin content in wine and eliminates inconvenient processes, such as calibrations and/or enzyme reactions. The Folin-Ciocalteau spectrophotometry (FCS) was used a positive control and compared it with new microelectrode biosensor cyclic voltammetry (MBCV) method. The new approach was established that not only allows for real-time tannin detection but is also economical and does not require the use of a specific enzyme. The results are reproducible and provide a precise measurement of tannin content.

Sensory Properties of Wine Tannin Fractions: Implications for In-Mouth Sensory Properties

Different molecular structures of grape tannins have been shown to influence astringency, however, the in-mouth sensory effects of different molecular structures in red wine tannins remains to be established. The objective of this research was to assess the impact of wine tannin structure on in-mouth sensory properties. Wine tannin was isolated from Cabernet Sauvignon wines of two vintages (3 and 7 years old) and separated into two structurally distinct subfractions with liquid-liquid fractionation using butanol and water. The aqueous subfractions had greater mean degree of polymerization (mDp) and contained a higher proportion of epigallocatechin subunits than the butanol-soluble subfractions, while the older wine tannin fractions showed fewer epicatechin gallate subunits than the younger tannin fractions. The red wine had approximately 3:1 mass ratio of the aqueous and butanol tannin subfractions which approximated an equimolar ratio of tannin in each subfraction. Descriptive sensory analysis of the tannin subfractions in model wine at equimolar concentrations revealed that the larger, more water-soluble wine tannin subfractions from both wines were perceived as more astringent than the smaller, more hydrophobic and more highly pigmented butanol-soluble subfractions, which were perceived as hotter and more bitter. Partial least squares analysis indicated that the greater hydrophobicity and color incorporation in the butanol fractions was negatively associated with astringency, and these characteristics are also associated with aged wine tannins. As the larger, water-soluble tannins had a greater impact on the overall wine astringency, winemaking processes that modulate concentrations of these are likely to most significantly influence astringency.

Oenological tannins: a review

This review is a state-of-the-art summary of current literature on the commercial oenological tannins that are often added to wine. These tannins can come from different origins, which affect their composition and characteristics. The two main sources of oenological tannins are grapes and oak wood. This review describes methods to quantify and characterise oenological tannins and indicates that these methods also need to be improved. These tannins have different interactions with proteins as well as with wine components such as anthocyanins and other phenolics in wine. The suppliers of commercial tannins often emphasise that these products can stabilise colour in red wine and influence the mouthfeel of the wine, among other things. The literature, however, suggests that the addition of these tannins often does not lead to large differences in the chemical profile of the wine and sometimes even leads to unwanted sensory characters being observed in the wine. More research clearly is needed regarding the role of oenological tannins in wine.

Relationships between harvest time and wine composition in Vitis vinifera L. cv. Cabernet Sauvignon 1. Grape and wine chemistry

The study aimed to quantify the effects of grape maturity on wine alcohol, phenolics, flavour compounds and polysaccharides in Vitis vinifera L. cv Cabernet Sauvignon. Grapes were harvested at juice soluble solids from 20 to 26 °Brix which corresponded to a range of wine ethanol concentrations between 12% and 15.5%. Grape anthocyanin and skin tannin concentration increased as ripening progressed, while seed tannin declined. In the corresponding wines, monomeric anthocyanin and wine tannin concentration increased with harvest date, consistent with an enhanced extraction of skin-derived phenolics. In wines, there was an observed increase in yeast-derived metabolites, including volatile esters, dimethyl sulfide, glycerol and mannoproteins with harvest date. Wine volatiles which were significantly influenced by harvest date were isobutyl methoxypyrazine, C6 alcohols and hexyl acetate, all of which decreased as ripening progressed. The implications of harvest date for wine composition is discussed in terms of both grape composition and yeast metabolism.

Phenolic Compositions of 50 and 30 Year Sequences of Australian Red Wines: The Impact of Wine Age

The phenolic composition of red wine impacts upon the color and mouthfeel and thus quality of the wine. Both of these characteristics differ depending on the age of a wine, with the purple of young wines changing to brick red and the puckering or aggressive astringency softening in older wines. This study investigated the color parameters, tannin concentrations and tannin composition of a 50 year series of Cabernet Sauvignon wines from a commercial label as well as 30 year series of Cabernet Sauvignon and Shiraz wines from a separate commercial label to assess the impact of wine age on phenolic composition and concentration. The wine color density in wines of 40 to 50 years old was around 5 AU compared with 16 AU of wine less than 12 months old, which correlated well with the concentration of non-bleachable pigments and pigmented polymers. Conversely, the anthocyanin concentrations in 10 year old wines were substantially lower than that of recently bottled wines (around 100 mg/L compared with 627 mg/L, respectively), adding further evidence that non-bleachable pigments including pigmented polymers play a much larger role in long-term wine color than anthocyanins. No age-related trend was observed for tannin concentration, indicating that the widely noted softer astringency of older red wines cannot necessarily be directly related to lower concentrations of soluble wine tannin and is potentially a consequence of changes in tannin structure. Wine tannins from older wines were generally larger than tannins from younger wines and showed structural changes consistent with oxidation.

Influence of berry ripeness on concentration, qualitative composition and extractability of grape seed tannins

Background and Aims: The evolution of seed tannins in three grape varieties grown in the same vineyard was followed from preveraison to harvest, to determine their pattern of accumulation. Also, to elucidate whether the use of 70% acetone as extracting solvent overestimate what will occur during fermentation, seed tannins were extracted throughout the ripening period with a method that involved a 3 days extraction with aqueous 12.5% ethanol and the results compared with the acetone extraction method. Methods and Results: For both methods, the extracted tannins were analysed following acid-catalysis in the presence of excess of phloroglucinol. Seed tannins reached a maximum around veraison and decreased towards maturity, the mean degree of polymerization (mDP) varying only slightly during the studied period. When tannins were extracted with 12.5% ethanol, their concentration was much higher during the first part of the maturation than using acetone but was significantly lower at harvest. Conclusions: The decrease in extractable seed tannins during ripening was observed with both solvents. The differences observed in the concentration of tannins with both solvents could be due to the histochemical changes occurring in seeds during maturation. Significance of the Study: The differences observed in tannin concentration with the two different methods may indicate that when pulp maturity is reached before seeds are ripe, the fermenting solution will extract more tannins than the acetone method. These results point to the importance of extraction methodology when monitoring seed maturity for the prediction of seed tannins in wine.

Impact of Shoot and Cluster Thinning on Yield, Fruit Composition, and Wine Quality of Corot noir

Cluster thinning (CL), shoot thinning (ST), and a combination of the two practices (ST+CL) were applied to vigorous Corot noir (hybrid sp.) winegrapes grown at a commercial vineyard in the Finger Lakes region of New York State. Yield was reduced by CL (by up to 4.8 kg/vine) but not ST in 2008, and by ST (by up to 2.0 kg/vine) and not CL in 2009; however, high pruning weights (up to 4.5 kg/vine in 2008) and low crop-load ratios (ranging from 2.3 to 7.1) indicated that vines in the study were undercropped regardless of treatment. CL increased soluble solids by up to 2.5 Brix in 2008 and by up to 0.8 Brix in the ST+CL treatment in 2009, while ST increased soluble solids in 2009 by 0.8 Brix. The treatments had variable impacts on wine anthocyanin, berry skin tannin, berry seed tannin, and wine tannin depending on year. Wine tannin (42 to 64 mg/L) and tannin extractability (5 to 6%) were both very low compared to values typically observed in red wines produced from V. vinifera. Using a two-alternative forced choice test, panelists reported ST+CL wines were fruitier than the control and ST wines and that ST wines were less fruity than the control in both years. An economic analysis indicated that in order for growers/wineries to maintain their economic welfare, bottle prices would have to increase by $0.02 to $0.41 depending on the practice and year to compensate for additional labor costs and lost yield in implementing these crop-load management practices.

Impact of exogenous tannin additions on wine chemistry and wine sensory character

Tannins are an important part of wine quality and are frequently added during winemaking. Tannin additives and their impact on wine are poorly documented. This work sought to characterize a range of enological tannins and their contribution to wine quality. Enological tannins were analysed for protein precipitable tannins and iron reactive phenolics. One tannin product was added to a Merlot wine during barrel ageing, at a range of concentrations from 60 to 300 mg/l. Condensed and hydrolysable tannins were added to Cabernet Sauvignon wine post-pressing at a recommended and excessive rate. Wines were analysed for anthocyanin, small and large polymeric pigment, precipitable tannin, iron reactive phenolics and sensory character. Enological tannins contained 12–48% tannin and recommended additions had little impact on wine tannin. High tannin additions were readily measured in the wines and were discriminated in sensory analysis with lower intensities of most parameters except brown colour, bitterness and earthy character. Recommended addition rates are too low to impact the measured tannin concentration of Merlot and Cabernet Sauvignon wines from Washington (USA). High enological tannin additions had a measureable impact on final wine had a negative impact on sensory character. Tannins are added to wines for a range of reasons and represent one of many input costs in an industry increasingly seeking efficiencies in response to global economic circumstances, over-supply and an ongoing price point squeeze. This research suggests many tannin additions may be unjustified and have limited or negative impacts on quality.

Impact of Concentration of Ellagitannins in Oak Wood on Their Levels and Organoleptic Influence in Red Wine

Some wood substances such as ellagitannins can be extracted during wine aging in oak barrels. The level of these hydrolyzable tannins in wine depends of some parameters of oak wood. Their impact on the organoleptic perception of red wine is poorly known. In our research, oak staves were classified in three different groups according to their level of ellagitannins estimated by NIRS (near infrared spectroscopy) online procedure (Oakscan). First, the ellagitannin level and composition were determine for each classified stave and an excellent correlation between the NIRS classification (low, medium and high potential level of ellagitannin) and the ellagitannin content estimated by HPLC-UV was found. Each different group of NIRS classified staves was then added to red wine during its aging in a stainless tank, and the extraction and evolution of the ellagitannins were monitored. A good correlation between the NIRS classification and the concentration of ellagitannins in red wine aging in contact with the classified staves was observed. The influence of levels of ellagitannins on the resulting wine perception was estimated by a trained judge's panel, and it reveals that the level of ellagitannins in wine has an impact on the roundness and amplitude of the red wine.

Quantification of glutathione, catechin and caffeic acid in grape juice and wine by a novel ultra-performance liquid chromatography method

This research aimed at the development and validation of an ultra-performance liquid chromatography (UPLC) method for the quantification of glutathione (GSH) in grape juice and in white wine after derivatisation with para-benzoquinone. The phenolic compounds catechin and caffeic acid that occur in white wine and have antioxidant effects, are also quantified in the same analysis. Catechin is the basic monomeric unit of grape and wine tannins and caffeic acid, when esterified with tartaric acid, plays a relevant role in Grape Reaction Product (GRP) formation.The analytical method proposed showed good linearity, repeatability and intermediate repeatability, as well as high recovery (>85%). It was applied for the quantification of GSH, catechin and caffeic acid in South African juices (12) and white wines (43).This novel method will have a large impact on the time and costs of the analyses for the wine industry through enabling rapid routine quantification of GSH, catechin and caffeic acid.

Effect of protein-tannin ratio and tannin concentration on the bovine serum albumin (BSA)-based precipitation method for red wine tannin concentration

<p style="text-align: justify;"><strong>Aims</strong>: The main objective of the study was to ascertain whether an existing protein precipitation assay could be simply modified to determine tannin at low concentration in wines. This was achieved by mixing a greater volume of wine to a smaller, but more concentrated, volume of bovine serum albumin (BSA) to maintain the same wine-to-BSA ratio (although both the final pH and ethanol concentration varied). In addition, dilution series of each of these mixtures were prepared to investigate the effect of wine-to-BSA ratio on tannin precipitation.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Seven New Zealand red wines were assayed according to the BSA method using a range of protein (BSA) and wine concentrations achieved by varying wine dilutions and the volume of the model wine solution. Maximum precipitation was observed at lower wine/protein ratios in diluted wines and tannin precipitation increased as protein concentration increased. It was observed that the estimation of tannin concentration in red wine is a product of tannin/protein ratio and BSA concentration. Consequently, the methylcellulose precipitation (MCP) assay was performed to independently determine tannin concentration in red wines. Results indicate that tannin/protein ratio, BSA concentration and possibly tannin composition affect BSA-tannin precipitation.</p><p style="text-align: justify;"><strong>Conclusion</strong>: For the BSA assay there appears to be a region of low tannin/protein ratio within which lower wine tannin concentrations can be determined. Overall it is suggested that tannin precipitation is linearly related to tannin concentration.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: Results showed the limits of the BSA method for low tannin wines and the difficulty in using the method for wines with unknown tannin concentrations.</p>

Wine and Grape Tannin Interactions with Salivary Proteins and Their Impact on Astringency: A Review of Current Research

Astringency is an important characteristic of red wine quality. The sensation is generally thought to be produced by the interaction of wine tannins with salivary proteins and the subsequent aggregation and precipitation of protein-tannin complexes. The importance of wine astringency for marketability has led to a wealth of research on the causes of astringency and how tannins impact the quality of the sensation, particularly with respect to tannin structure. Ultimately, the understanding of how tannin structure impacts astringency will allow the controlled manipulation of tannins via such methods as micro-oxygenation or fining to improve the quality of wines.

Thermodynamics of Grape and Wine Tannin Interaction with Polyproline: Implications for Red Wine Astringency

The astringency of red wine is largely due to the interaction between wine tannins and salivary proline-rich proteins and is known to change as wine ages. To further understand the mechanisms behind wine astringency change over time, thermodynamics of the interactions between poly(l-proline) (PLP) and grape seed and skin tannins (preveraison (PV) and commercially ripe) or Shiraz wine tannins (2 years old and 9-10 years old) was analyzed using isothermal titration calorimetry (ITC). The nature of these interactions varied with changes to the tannin structure that are associated with maturation. The change in enthalpy associated with hydrophobic interaction and hydrogen bonding decreased with tannin age and the stoichiometry of binding indicated that grape tannins associated with more proline residues than wine tannins, irrespective of molecular size. These results could provide an explanation for the observed change in wine astringency quality with age.

Flavonoids and C13-norisoprenoids in Vitis vinifera L. cv. Shiraz: relationships between grape and wine composition, wine colour and wine sensory properties

Background and Aims: This study investigated flavonoid composition and C13-norisoprenoids (β-damascenone and β-ionone) in Shiraz grapes and wines, their relationships and links to wine sensory properties. Methods and Results: Differences in the grape berry flavonoid profile were created by exposing bunches to varying levels of sunlight intensity through canopy manipulation. Grapes were harvested at similar maturity and three replicate wines were made for each treatment in both vintages. Grapes produced under shaded canopy conditions had reduced anthocyanins and skin tannins, but little effect on seed tannins was observed. Pigmented polymers and tannins in wines were related to berry flavonoid composition (anthocyanins, skin and seed tannins, and their ratios). In grapes and wines, no significant effects were observed in response to canopy manipulation for two hydrolytically released C13-norisoprenoids, β-damascenone and β-ionone. Relationships were established for wine flavonoid composition, wine colour density, sensory perception of the astringency-related mouth-feel attributes and a quality scale. A positive relationship between wine quality score and hydrolytically released β-damascenone in both berries and wines was found, but not for free β-damascenone or any quantified forms of β-ionone. Conclusion: Higher concentrations of anthocyanins and skin tannins in berries, coupled with a lower concentration of seed tannins were associated with higher wine quality. The ratio anthocyanins*skin tannins/seed tannins is proposed as an indicator of wine flavonoid composition, wine colour and wine quality. Excessive canopy shade was detrimental to berry and wine composition and intensified sensory detection of ‘straw’ and ‘herbaceous’ characters in the wines. Significance of the Study: This study increases the understanding of the balance and composition of flavonoid compounds and C13-norisoprenoids in berries and their relationship with wine composition and wine sensory properties, but also highlights the importance of a canopy microclimate assessment.

NMR and molecular modeling of wine tannins binding to saliva proteins: revisiting astringency from molecular and colloidal prospects

In organoleptic science, the association of tannins to saliva proteins leads to the poorly understood phenomenon of astringency. To decipher this interaction at molecular and colloidal levels, the binding of 4 procyanidin dimers (B1-4) and 1 trimer (C2) to a human saliva proline-rich peptide, IB7(14), was studied. Interactions have been characterized by measuring dissociation constants, sizes of complexes, number, and nature of binding sites using NMR (chemical shift variations, diffusion-ordered spectroscopy, and saturation transfer diffusion). The binding sites were identified using molecular mechanics, and the hydrophilic/hydrophobic nature of the interactions was resolved by calculating the molecular lipophilicity potential within the complexes. The following comprehensive scheme can be proposed: 1) below the tannin critical micelle concentration (CMC), interaction is specific, and the procyanidin anchorage always occurs on the same three IB7(14) sites. The tannin 3-dimensional structure plays a key role in the binding force and in the tannin's ability to act as a bidentate ligand: tannins adopting an extended conformation exhibit higher affinity toward protein and initiate the formation of a network. 2) Above the CMC, after the first specific hydrophilic interaction has taken place, a random hydrophobic stacking occurs between tannins and proteins. The whole process is discussed in the general frame of wine tannins eliciting astringency.

Colloidal behavior of wine galloylated tannins

Tannins are one of the four key components determining wine organoleptic quality. First, they play an important gustative role since they are responsible for wine astringency and/or bitterness. Second, they act as a structuring compound directly linked to red wine turbidity and stability. This second role is the consequence of their colloidal behavior. In the present work, we demonstrate that wine tannins exhibit different colloidal behaviour whether they are or not galloylated. Procyanidins, when galloylated, are more inclined to form micelles than their non-galloylated form, letting us suggest that they could act as structuring agent in wine. However, the size of the formed micelles is of the nanometer range suggesting that procyanidins, up to trimers, are not involved alone in wine turbidity. Les tannins sont l’un des quatre composants déterminant la qualité organoleptique des vins rouges. Ils y joueraient deux rôles clefs ; l’un gustatif, en apportant au vin astringence et amertume et l’autre structurant du fait de leur capacité à s’auto-associer pour former des micelles. Ces micelles, si elles atteignent la taille micrométrique, peuvent également jouer un rôle dans la turbidité des vins. Dans le présent travail, nous avons suivi le comportement colloïdal de tannins catéchiques galloylés par RMN DOSY, mesuré leur constante d’association Ka ainsi que leur concentration micellaire critique (CMC) et enfin, estimé la taille des micelles formées. Nous avons pu montrer à travers ces expériences que les tannins galloylés sont plus enclins que leurs homologues non galloylés à former des micelles aux concentrations trouvées dans le vin. En revanche, la taille des micelles formées reste faible (rayon de l’ordre de 2 nm), ce qui laisse penser que les tannins, même s’ils sont capables de structurer le vin en s’auto-associant, ne jouent pas, seuls, un rôle dans la turbidité des vins.

Heating and reduction affect the reaction with tannins of wine protein fractions differing in hydrophobicity

During the storage, bottled white wines can manifest haziness due to the insolubilisation of the grape proteins that may ‘survive’ in the fermentation process. Although the exact mechanism of this occurrence is not fully understood, proteins and tannins are considered two of the key factors involved in wine hazing, since their aggregation leads to the formation of insoluble particles. To better understand this complex interaction, proteins and tannins from the same unfined Pinot grigio wine were separated. Wine proteins were then fractionated by hydrophobic interaction chromatography (HIC). A significant correlation between hydrophobicity of the wine protein fractions and the haze formed after reacting with wine tannins was found, with the most reactive fractions revealing (by SDS-PAGE and RP-HPLC analyses) the predominant presence of thaumatin-like proteins. Moreover, the effects of both protein heating and disulfide bonds reduction (with dithiotreithol) on haze formation in the presence of tannins were assessed. These treatments generally resulted in an improved reactivity with tannins, and this phenomenon was related to both the surface hydrophobicity and composition of the protein fractions. Therefore, haze formation in wines seems to be related to hydrophobic interactions occurring among proteins and tannins. These interactions should occur on hydrophobic tannin-binding sites, whose exposition on the proteins can depend on both protein heating and reduction.