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{{Short description|Wine chemistry}} |
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[[File:Shiraz Grapes.jpg|250px|thumb|The phenolic compounds in Syrah grapes contribute to the taste, color and mouthfeel of the wine.]] |
[[File:Shiraz Grapes.jpg|250px|thumb|The phenolic compounds in Syrah grapes contribute to the taste, color and mouthfeel of the wine.]] |
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The '''phenolic content in wine''' refers to the phenolic compounds—[[natural phenol]] and [[polyphenol]]s—in [[wine]], which include a large group of several hundred [[chemical compound]]s that affect the [[taste (wine)|taste]], [[color (wine)|color]] and [[mouthfeel (wine)|mouthfeel]] of wine. These compounds include [[phenolic acid]]s, [[stilbenoid]]s, [[flavonol]]s, [[dihydroflavonol]]s, [[anthocyanin]]s, [[flavanol]] monomers ([[catechin]]s) and [[flavanol]] polymers ([[proanthocyanidin]]s). This large group of natural phenols can be broadly separated into two categories, [[flavonoid]]s and non-flavonoids. Flavonoids include the [[anthocyanin]]s and [[tannin]]s which contribute to the color and mouthfeel of the wine.<ref>{{cite journal |vauthors=Kennedy JA, Matthews MA, Waterhouse AL |title=Effect of Maturity and Vine Water Status on Grape Skin and Wine Flavonoids |journal=Am. J. Enol. Vitic. |volume=53 |issue=4 |pages=268–74 |year=2002 |url=http://www.ajevonline.org/cgi/content/abstract/53/4/268}}</ref> The non-flavonoids include the [[stilbenoid]]s such as [[resveratrol]] and [[phenolic acid]]s such as [[benzoic (acid)|benzoic]], [[caffeic acid|caffeic]] and [[cinnamic acid|cinnamic]] acids. |
The '''phenolic content in wine''' refers to the phenolic compounds—[[natural phenol]] and [[polyphenol]]s—in [[wine]], which include a large group of several hundred [[chemical compound]]s that affect the [[taste (wine)|taste]], [[color (wine)|color]] and [[mouthfeel (wine)|mouthfeel]] of wine. These compounds include [[phenolic acid]]s, [[stilbenoid]]s, [[flavonol]]s, [[dihydroflavonol]]s, [[anthocyanin]]s, [[flavanol]] monomers ([[catechin]]s) and [[flavanol]] polymers ([[proanthocyanidin]]s). This large group of natural phenols can be broadly separated into two categories, [[flavonoid]]s and non-flavonoids. Flavonoids include the [[anthocyanin]]s and [[tannin]]s which contribute to the color and mouthfeel of the wine.<ref>{{cite journal |vauthors=Kennedy JA, Matthews MA, Waterhouse AL |title=Effect of Maturity and Vine Water Status on Grape Skin and Wine Flavonoids |journal=Am. J. Enol. Vitic. |volume=53 |issue=4 |pages=268–74 |year=2002 |doi=10.5344/ajev.2002.53.4.268 |s2cid=10545757 |url=http://www.ajevonline.org/cgi/content/abstract/53/4/268}}</ref> The non-flavonoids include the [[stilbenoid]]s such as [[resveratrol]] and [[phenolic acid]]s such as [[benzoic (acid)|benzoic]], [[caffeic acid|caffeic]] and [[cinnamic acid|cinnamic]] acids. |
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== Origin of the phenolic compounds == |
== Origin of the phenolic compounds == |
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The natural phenols are not evenly distributed within the fruit. Phenolic acids are largely present in the pulp, [[anthocyanin]]s and [[stilbenoid]]s in the skin, and other phenols ([[catechin]]s, [[proanthocyanidin]]s and [[flavonol]]s) in the skin and the seeds.<ref>{{cite journal|doi=10.1021/jf504185s | pmid=25417599 | volume=62 | issue=50 | title=Low Molecular Weight Phenolics of Grape Juice and Winemaking Byproducts: Antioxidant Activities and Inhibition of Oxidation of Human Low-Density Lipoprotein Cholesterol and DNA Strand Breakage | year=2014 | journal=Journal of Agricultural and Food Chemistry | pages=12159–12171 | last1 = Costa de Camargo | first1 = Adriano | last2 = Bismara Regitano-d'Arce | first2 = Marisa Aparecida | last3 = Camarão Telles Biasoto | first3 = Aline | last4 = Shahidi | first4 = Fereidoon}}</ref> During the [[growth cycle of the grapevine]], sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of [[canopy management]]. The proportion of the different phenols in any one wine will therefore vary according to the type of [[vinification]]. [[Red wine]] will be richer in phenols abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols, whereas the phenols in [[white wine]] will essentially originate from the pulp, and these will be the phenolic acids together with lower amounts of catechins and stilbenes. Red wines will also have the phenols found in white wines. |
The natural phenols are not evenly distributed within the fruit. Phenolic acids are largely present in the pulp, [[anthocyanin]]s and [[stilbenoid]]s in the skin, and other phenols ([[catechin]]s, [[proanthocyanidin]]s and [[flavonol]]s) in the skin and the seeds.<ref>{{cite journal|doi=10.1021/jf504185s | pmid=25417599 | volume=62 | issue=50 | title=Low Molecular Weight Phenolics of Grape Juice and Winemaking Byproducts: Antioxidant Activities and Inhibition of Oxidation of Human Low-Density Lipoprotein Cholesterol and DNA Strand Breakage | year=2014 | journal=Journal of Agricultural and Food Chemistry | pages=12159–12171 | last1 = Costa de Camargo | first1 = Adriano | last2 = Bismara Regitano-d'Arce | first2 = Marisa Aparecida | last3 = Camarão Telles Biasoto | first3 = Aline | last4 = Shahidi | first4 = Fereidoon}}</ref> During the [[growth cycle of the grapevine]], sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of [[canopy management]]. The proportion of the different phenols in any one wine will therefore vary according to the type of [[vinification]]. [[Red wine]] will be richer in phenols abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols, whereas the phenols in [[white wine]] will essentially originate from the pulp, and these will be the phenolic acids together with lower amounts of catechins and stilbenes. Red wines will also have the phenols found in white wines. |
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Wine simple phenols are further transformed during [[aging of wine|wine aging]] into complex molecules formed notably by the condensation of proanthocyanidins and anthocyanins, which explains the modification in the color. Anthocyanins react with catechins, proanthocyanidins and other wine components during wine aging to form new polymeric pigments resulting in a modification of the wine color and a lower astringency.<ref>{{cite journal |vauthors=Cheynier V, Duenas-Paton M, Salas E, Maury C, Souquet JM, Sarni-Manchado P, Fulcrand H |title=Structure and properties of wine pigments and tannins |journal=American Journal of Enology and Viticulture |volume=57 |pages=298–305 |year=2006 }}</ref><ref>{{cite journal |vauthors=Fulcrand H, Duenas M, Salas E, Cheynier V |title=Phenolic reactions during winemaking and aging |journal=American Journal of Enology and Viticulture |volume=57 |pages=289–297 |year=2006 }}</ref> Average total polyphenol content measured by the [[Folin-Ciocalteu reagent|Folin]] method is 216 mg/100 ml for red wine and 32 mg/100 ml for white wine. The content of phenols in rosé wine (82 mg/100 ml) is intermediate between that in red and white wines. |
Wine simple phenols are further transformed during [[aging of wine|wine aging]] into complex molecules formed notably by the condensation of proanthocyanidins and anthocyanins, which explains the modification in the color. Anthocyanins react with catechins, proanthocyanidins and other wine components during wine aging to form new polymeric pigments resulting in a modification of the wine color and a lower [[astringency]].<ref>{{cite journal |vauthors=Cheynier V, Duenas-Paton M, Salas E, Maury C, Souquet JM, Sarni-Manchado P, Fulcrand H |title=Structure and properties of wine pigments and tannins |journal=American Journal of Enology and Viticulture |volume=57 |pages=298–305 |year=2006 |issue=3 |doi=10.5344/ajev.2006.57.3.298 |s2cid=84044849 |doi-access=free }}</ref><ref>{{cite journal |vauthors=Fulcrand H, Duenas M, Salas E, Cheynier V |title=Phenolic reactions during winemaking and aging |journal=American Journal of Enology and Viticulture |volume=57 |pages=289–297 |year=2006 |issue=3 |doi=10.5344/ajev.2006.57.3.289 |s2cid=86822376 |doi-access=free }}</ref> Average total polyphenol content measured by the [[Folin-Ciocalteu reagent|Folin]] method is 216 mg/100 ml for red wine and 32 mg/100 ml for white wine. The content of phenols in rosé wine (82 mg/100 ml) is intermediate between that in red and white wines. |
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In [[winemaking]], the process of [[maceration (wine)|maceration]] or "skin contact" is used to increase the concentration of phenols in wine. Phenolic acids are found in the pulp or juice of the wine and can be commonly found in white wines which usually do not go through a maceration period. The process of [[oak (wine)|oak aging]] can also introduce phenolic compounds into wine, most notably [[vanillin]] which adds [[vanilla]] [[aroma (wine)|aroma]] to wines.<ref name="Oxford |
In [[winemaking]], the process of [[maceration (wine)|maceration]] or "skin contact" is used to increase the concentration of phenols in wine. Phenolic acids are found in the pulp or juice of the wine and can be commonly found in white wines which usually do not go through a maceration period. The process of [[oak (wine)|oak aging]] can also introduce phenolic compounds into wine, most notably [[vanillin]] which adds [[vanilla]] [[aroma (wine)|aroma]] to wines.<ref name="Oxford pp 517-518">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, pp 517-518. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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Most wine phenols are classified as [[secondary metabolite]]s and were not thought to be active in the primary [[metabolism]] and function of the grapevine. However, there is evidence that in some plants [[flavonoid]]s play a role as endogenous regulators of [[auxin]] transport.<ref name="pmid11402184">{{cite journal |author=Brown DE |title=Flavonoids act as negative regulators of auxin transport in vivo in arabidopsis |journal=Plant Physiol. |volume=126 |issue=2 |pages=524–35 |date=June 2001 |pmid=11402184 |pmc=111146 |doi= 10.1104/pp.126.2.524 |
Most wine phenols are classified as [[secondary metabolite]]s and were not thought to be active in the primary [[metabolism]] and function of the grapevine. However, there is evidence that in some plants [[flavonoid]]s play a role as endogenous regulators of [[auxin]] transport.<ref name="pmid11402184">{{cite journal |author=Brown DE |title=Flavonoids act as negative regulators of auxin transport in vivo in arabidopsis |journal=Plant Physiol. |volume=126 |issue=2 |pages=524–35 |date=June 2001 |pmid=11402184 |pmc=111146 |doi= 10.1104/pp.126.2.524|name-list-style=vanc|author2=Rashotte AM |author3=Murphy AS |display-authors=3 |last4=Normanly |first4=J |last5=Tague |first5=BW |last6=Peer |first6=WA |last7=Taiz |first7=L |last8=Muday |first8=GK}}</ref> They are [[water-soluble]] and are usually secreted into the [[vacuole]] of the grapevine as [[glycosides]]. |
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== Grape polyphenols == |
== Grape polyphenols == |
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{{Main|Flavonoids}} |
{{Main|Flavonoids}} |
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[[File:Red wine cap.jpg|left|250px|thumb|The process of [[maceration (wine)|maceration]] or extended skin contact allows the extraction of phenolic compounds (including those that form a wine's color) from the skins of the grape into the wine.]] |
[[File:Red wine cap.jpg|left|250px|thumb|The process of [[maceration (wine)|maceration]] or extended skin contact allows the extraction of phenolic compounds (including those that form a wine's color) from the skins of the grape into the wine.]] |
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In red wine, up to 90% of the wine's phenolic content falls under the classification of flavonoids. These phenols, mainly derived from the stems, seeds and skins are often leached out of the grape during the maceration period of winemaking. The amount of phenols leached is known as [[extraction ( |
In red wine, up to 90% of the wine's phenolic content falls under the classification of flavonoids. These phenols, mainly derived from the stems, seeds and skins are often leached out of the grape during the maceration period of winemaking. The amount of phenols leached is known as [[extraction (chemistry)|extraction]]. These compounds contribute to the [[astringency]], color and mouthfeel of the wine. In white wines the number of flavonoids is reduced due to the lesser contact with the skins that they receive during winemaking. There is on-going study into the [[health benefits of wine]] derived from the [[antioxidant]] and [[chemopreventive]] properties of flavonoids.<ref name="Oxford pp 273-274">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, pp. 273-274. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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==== Flavonols ==== |
==== Flavonols ==== |
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{{Main|Flavonols}} |
{{Main|Flavonols}} |
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Within the flavonoid category is a subcategory known as [[flavonol]]s, which includes the yellow [[pigment]] - [[quercetin]]. Like other flavonoids, the concentration of flavonols in the grape berries increases as they are exposed to sunlight. Some [[viticulturalist]]s will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques. |
Within the flavonoid category is a subcategory known as [[flavonol]]s, which includes the yellow [[pigment]] - [[quercetin]]. Like other flavonoids, the concentration of flavonols in the grape berries increases as they are exposed to sunlight. Wine grapes facing too much sun exposure can see an accelerated ripening period, leading to a lessened ability for the synthesis of flavonols.<ref name="Gutiérrez-Gamboa 109946">{{Cite journal |last1=Gutiérrez-Gamboa |first1=Gastón |last2=Zheng |first2=Wei |last3=Martínez de Toda |first3=Fernando |date=January 2021 |title=Current viticultural techniques to mitigate the effects of global warming on grape and wine quality: A comprehensive review |url=http://dx.doi.org/10.1016/j.foodres.2020.109946 |journal=Food Research International |volume=139 |pages=109946 |doi=10.1016/j.foodres.2020.109946 |pmid=33509499 |hdl=10261/229725 |s2cid=230556619 |issn=0963-9969|hdl-access=free }}</ref> Some [[viticulturalist]]s will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques. |
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==== Anthocyanins ==== |
==== Anthocyanins ==== |
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{{Main|Anthocyanin}} |
{{Main|Anthocyanin}} |
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Anthocyanins are phenolic compounds found throughout the [[plant kingdom]], being frequently responsible for the blue to red colors found in [[flower]]s, [[fruit]]s and [[leaf|leaves]]. In wine grapes, they develop during the stage of ''[[veraison]]'' when the skin of red wine grapes changes color from green to red to black. As the [[sugar in wine|sugars in the grape]] increase during [[ripening (wine)|ripening]] so does the concentration of anthocyanins. In most grapes anthocyanins are found only in the outer cell layers of the skin, leaving the grape juice inside virtually colorless. Therefore, to get color pigmentation in the wine, the [[fermentation (wine)|fermenting]] [[must]] needs to be in contact with the grape skins in order for the anthocyanins to be extracted. Hence, white wine can be made from red wine grapes in the same way that many white [[sparkling wine]]s are made from the red wine grapes of [[Pinot noir]] and [[Pinot Meunier]]. The exception to this is the small class of grapes known as [[teinturier]]s, such as [[Alicante Bouschet]], which have a small amount of anthocyanins in the pulp that produces pigmented juice.<ref name="Oxford |
Anthocyanins are phenolic compounds found throughout the [[plant kingdom]], being frequently responsible for the blue to red colors found in [[flower]]s, [[fruit]]s and [[leaf|leaves]]. In wine grapes, they develop during the stage of ''[[veraison]],'' when the skin of red wine grapes changes color from green to red to black. As the [[sugar in wine|sugars in the grape]] increase during [[ripening (wine)|ripening]] so does the concentration of anthocyanins. An issue associated with climate change has been the accumulation of sugars within the grape accelerating rapidly and outpacing the accumulation of anthocyanins.<ref name="Gutiérrez-Gamboa 109946"/> This leaves viticulturists with the choice of harvesting grapes with too high sugar content or with too low anthocyanin content. In most grapes anthocyanins are found only in the outer cell layers of the skin, leaving the grape juice inside virtually colorless. Therefore, to get color pigmentation in the wine, the [[fermentation (wine)|fermenting]] [[must]] needs to be in contact with the grape skins in order for the anthocyanins to be extracted. Hence, white wine can be made from red wine grapes in the same way that many white [[sparkling wine]]s are made from the red wine grapes of [[Pinot noir]] and [[Pinot Meunier]]. The exception to this is the small class of grapes known as [[teinturier]]s, such as [[Alicante Bouschet]], which have a small amount of anthocyanins in the pulp that produces pigmented juice.<ref name="Oxford p 24">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p.24. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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There are several types of anthocyanins (as the [[glycoside]]) found in wine grapes which are responsible for the vast range of coloring from ruby red through to dark black found in wine grapes. [[Ampelographer]]s can use this observation to assist in the identification of different [[grape varieties]]. The European vine family ''[[Vitis vinifera]]'' is characterized by anthocyanins that are composed of only one molecule of [[glucose]] while non-''vinifera'' vines such as [[hybrids (grape)|hybrids]] and the American ''[[Vitis labrusca]]'' will have anthocyanins with two molecules. This phenomenon is due to a double mutation in the [[anthocyanin 5-O-glucosyltransferase]] gene of ''V. vinifera''.<ref>{{Cite journal|pmid=19338353|doi=10.1021/jf900146a|title=A Double Mutation in the Anthocyanin 5-O-Glucosyltransferase Gene Disrupts Enzymatic Activity in Vitis vinifera L|year=2009|last1=JáNváRy|first1=LáSzló|last2=Hoffmann|first2=Thomas|last3=Pfeiffer|first3=Judith|last4=Hausmann|first4=Ludger|last5=TöPfer|first5=Reinhard|last6=Fischer|first6=Thilo C.|last7=Schwab|first7=Wilfried|journal=Journal of Agricultural and Food Chemistry|volume=57|issue=9|pages=3512–8}}</ref> In the mid-20th century, French ampelographers used this knowledge to test the various vine varieties throughout France to identify which vineyards still contained non-''vinifera'' plantings.<ref name="Oxford |
There are several types of anthocyanins (as the [[glycoside]]) found in wine grapes which are responsible for the vast range of coloring from ruby red through to dark black found in wine grapes. [[Ampelographer]]s can use this observation to assist in the identification of different [[grape varieties]]. The European vine family ''[[Vitis vinifera]]'' is characterized by anthocyanins that are composed of only one molecule of [[glucose]] while non-''vinifera'' vines such as [[hybrids (grape)|hybrids]] and the American ''[[Vitis labrusca]]'' will have anthocyanins with two molecules. This phenomenon is due to a double mutation in the [[anthocyanin 5-O-glucosyltransferase]] gene of ''V. vinifera''.<ref>{{Cite journal|pmid=19338353|doi=10.1021/jf900146a|title=A Double Mutation in the Anthocyanin 5-O-Glucosyltransferase Gene Disrupts Enzymatic Activity in Vitis vinifera L|year=2009|last1=JáNváRy|first1=LáSzló|last2=Hoffmann|first2=Thomas|last3=Pfeiffer|first3=Judith|last4=Hausmann|first4=Ludger|last5=TöPfer|first5=Reinhard|last6=Fischer|first6=Thilo C.|last7=Schwab|first7=Wilfried|journal=Journal of Agricultural and Food Chemistry|volume=57|issue=9|pages=3512–8}}</ref> In the mid-20th century, French ampelographers used this knowledge to test the various vine varieties throughout France to identify which vineyards still contained non-''vinifera'' plantings.<ref name="Oxford p 24"/> |
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Red-berried [[Pinot (grape)|Pinot grape]] varieties are also known to not synthesize [[para-coumaroylated anthocyanin|para-coumaroylated]] or [[acetylated anthocyanin]]s as other varieties do.<ref>{{Cite journal|doi=10.3390/molecules15129057|title=Biosynthesis of Anthocyanins and Their Regulation in Colored Grapes|year=2010|last1=He|first1=Fei|last2=Mu|first2=Lin|last3=Yan|first3=Guo-Liang|last4=Liang|first4=Na-Na|last5=Pan|first5=Qiu-Hong|last6=Wang|first6=Jun|last7=Reeves|first7=Malcolm J.|last8=Duan|first8=Chang-Qing|journal=Molecules|volume=15|issue=12|pages=9057–91|pmid=21150825|pmc=6259108}}</ref> |
Red-berried [[Pinot (grape)|Pinot grape]] varieties are also known to not synthesize [[para-coumaroylated anthocyanin|para-coumaroylated]] or [[acetylated anthocyanin]]s as other varieties do.<ref>{{Cite journal|doi=10.3390/molecules15129057|title=Biosynthesis of Anthocyanins and Their Regulation in Colored Grapes|year=2010|last1=He|first1=Fei|last2=Mu|first2=Lin|last3=Yan|first3=Guo-Liang|last4=Liang|first4=Na-Na|last5=Pan|first5=Qiu-Hong|last6=Wang|first6=Jun|last7=Reeves|first7=Malcolm J.|last8=Duan|first8=Chang-Qing|journal=Molecules|volume=15|issue=12|pages=9057–91|pmid=21150825|pmc=6259108|doi-access=free }}</ref> |
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[[File:Tempranillowine.jpg|right|thumb|[[Tempranillo]] has a high pH level which means that there is a higher concentration of blue and colorless anthocyanin pigments in the wine. The resulting wine's coloring will have more blue hues than bright ruby red hues.]] |
[[File:Tempranillowine.jpg|right|thumb|[[Tempranillo]] has a high pH level which means that there is a higher concentration of blue and colorless anthocyanin pigments in the wine. The resulting wine's coloring will have more blue hues than bright ruby red hues.]] |
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The color variation in the finished red wine is partly derived from the [[ionization]] of anthocyanin pigments caused by the [[acidity (wine)|acidity]] of the wine. In this case, the three types of anthocyanin pigments are red, blue and colorless with the concentration of those various pigments dictating the color of the wine. A wine with low [[pH]] (and such greater acidity) will have a higher occurrence of ionized anthocyanins which will increase the amount of bright red pigments. Wines with a higher pH will have a higher concentration of blue and colorless pigments. As the [[Aging of wine|wine ages]], anthocyanins will react with other acids and compounds in wines such as tannins, [[pyruvic acid]] and [[acetaldehyde]] which will change the color of the wine, causing it to develop more "brick red" hues. These molecules will link up to create [[polymer]]s that eventually exceed their [[solubility]] and become sediment at the bottom of wine bottles.<ref name="Oxford |
The color variation in the finished red wine is partly derived from the [[ionization]] of anthocyanin pigments caused by the [[acidity (wine)|acidity]] of the wine. In this case, the three types of anthocyanin pigments are red, blue and colorless with the concentration of those various pigments dictating the color of the wine. A wine with low [[pH]] (and such greater acidity) will have a higher occurrence of ionized anthocyanins which will increase the amount of bright red pigments. Wines with a higher pH will have a higher concentration of blue and colorless pigments. As the [[Aging of wine|wine ages]], anthocyanins will react with other acids and compounds in wines such as tannins, [[pyruvic acid]] and [[acetaldehyde]] which will change the color of the wine, causing it to develop more "brick red" hues. These molecules will link up to create [[polymer]]s that eventually exceed their [[solubility]] and become sediment at the bottom of wine bottles.<ref name="Oxford p 24"/> [[Pyranoanthocyanins]] are chemical compounds formed in red [[wine]]s by [[yeast (wine)|yeast]] during [[Fermentation (wine)|fermentation]] processes<ref>{{cite journal | doi = 10.1016/j.chroma.2006.09.011 | volume=1134 | title=Isolation and quantification of oligomeric pyranoanthocyanin-flavanol pigments from red wines by combination of column chromatographic techniques | year=2006 | journal=Journal of Chromatography A | pages=215–225 | last1 = He | first1 = Jingren | issue=1–2 | pmid=16997314}}</ref> or during [[Microoxygenation|controlled oxygenation]] processes<ref>{{cite journal | doi = 10.1016/S0003-2670(01)01617-8 | volume=458 | title=Effect of oxygenation on polyphenol changes occurring in the course of wine-making | year=2002 | journal=Analytica Chimica Acta | pages=15–27 | last1 = Atanasova | first1 = Vessela}}</ref> during the [[aging of wine]].<ref>{{cite journal | doi = 10.1016/S0031-9422(03)00518-1 | volume=64 | title=Why are grape/fresh wine anthocyanins so simple and why is it that red wine color lasts so long? | year=2003 | journal=Phytochemistry | pages=1179–1186 | last1 = Brouillard | first1 = R. | issue=7 | pmid=14599515}}</ref> |
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==== Tannins ==== |
==== Tannins ==== |
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{{main|Tannin}} |
{{main|Tannin}} |
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Tannins refer to the diverse group of chemical compounds in wine that can affect the color, aging ability and texture of the wine. While tannins cannot be smelled or tasted, they can be perceived during [[wine tasting]] by the [[Touch|tactile]] |
Tannins refer to the diverse group of chemical compounds in wine that can affect the color, aging ability and texture of the wine. While tannins cannot be smelled or tasted, they can be perceived during [[wine tasting]] by the [[Touch|tactile]] sensation of [[astringency]] and sense of bitterness that they can leave in the mouth. This is due to the tendency of tannins to react with [[protein]]s, such as the ones found in [[saliva]].<ref>{{Cite journal|doi=10.1021/jf9805146|title=Interactions of Grape Seed Tannins with Salivary Proteins|year=1999|last1=Sarni-Manchado|first1=Pascale|last2=Cheynier|first2=Véronique|last3=Moutounet|first3=Michel|journal=Journal of Agricultural and Food Chemistry|volume=47|pages=42–7|pmid=10563846|issue=1}}</ref> In [[food and wine pairing]], foods that are high in proteins (such as [[red meat]]) are often paired with tannic wines to minimize the astringency of tannins. However, many wine drinkers find the perception of tannins to be a positive trait—especially as it relates to mouthfeel. The management of tannins in the winemaking process is a key component in the resulting quality.<ref name="Oxford p 680">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 680. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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Tannins are found in the skin, stems, and seeds of wine grapes but can also be introduced to the wine through the use of oak barrels and chips or with the addition of tannin powder. The natural tannins found in grapes are known as [[proanthocyanidin]]s due to their ability to release red anthocyanin pigments when they are heated in an acidic solution. Grape extracts are mainly rich in monomers and small oligomers (mean degree of polymerization <8). Grape seed extracts contain three monomers (catechin, epicatechin and epicatechin gallate) and procyanidin oligomers. Grape skin extracts contain four monomers (catechin, epicatechin, gallocatechin and epigallocatechin), as well as [[procyanidin]]s and [[prodelphinidin]]s oligomers.<ref name="M2009">{{cite journal |author1=Mattivi F. |author2=Vrhovsek U. |author3=Masuero D. |author4=Trainotti D. |title=Differences in the amount and structure of extractable skin and seed tannins amongst red grape cultivars |journal=Australian Journal of Grape and Wine Research |volume=15 |pages=27–35 |year=2009 |doi=10.1111/j.1755-0238.2008.00027.x}}</ref> The tannins are formed by [[enzymes]] during metabolic processes of the grapevine. The amount of tannins found naturally in grapes varies depending on the variety with [[Cabernet Sauvignon]], [[Nebbiolo]], [[Syrah]] and [[Tannat]] being 4 of the most tannic grape varieties. The reaction of tannins and anthocyanins with the phenolic compound [[catechin]]s creates another class of tannins known as '''pigmented tannins''' which influence the color of red wine.<ref name="cat.inist.fr">Compositional investigation of pigmented tannin. Kennedy James A. and Hayasaka Yoji, A.C.S. symposium series, 2004, vol. 886, pp. 247-264, {{INIST|16184447}}</ref> Commercial preparations of tannins, known as ''enological tannins'', made from [[oak wood]], [[grape]] seed and skin, plant [[gall]], [[chestnut]], [[quebracho tannin|quebracho]], [[Uncaria gambir|gambier]]<ref name="Luz Sanz M. 2008, pp. 778-783">Identification of the origin of commercial enological tannins by the analysis of monosaccharides and polyalcohols. Luz Sanz M., Martinez-Castro Isabel and Moreno-Arribas M. Victoria, Food chemistry, 2008, vol. 111, no3, pp. 778-783, {{INIST|20520307}}</ref> and [[myrobalan]] fruits,<ref name="ajevonline.org">{{cite journal | last1 = Marie-hélène | first1 = Salagoity-Auguste | last2 = Tricard | first2 = Christian | last3 = Marsal | first3 = Frédéric | last4 = Sudraud | first4 = Pierre | year = 1986 | title = Preliminary Investigation for the Differentiation of Enological Tannins According to Botanical Origin: Determination of Gallic Acid and Its Derivatives | url = http://www.ajevonline.org/cgi/content/abstract/37/4/301 | journal = Am. J. Enol. Vitic | volume = 37 | issue = 4| pages = 301–303 }}</ref> can be added at different stages of the wine production to improve color durability. The tannins derived from oak influence are known as "hydrolysable tannins" being created from the [[ellagic (acid)|ellagic]] and [[gallic acid]] found in the wood.<ref name="Oxford |
Tannins are found in the skin, stems, and seeds of wine grapes but can also be introduced to the wine through the use of oak barrels and chips or with the addition of tannin powder. The natural tannins found in grapes are known as [[proanthocyanidin]]s due to their ability to release red anthocyanin pigments when they are heated in an acidic solution. Grape extracts are mainly rich in monomers and small oligomers (mean degree of polymerization <8). Grape seed extracts contain three monomers (catechin, epicatechin and epicatechin gallate) and procyanidin oligomers. Grape skin extracts contain four monomers (catechin, epicatechin, gallocatechin and epigallocatechin), as well as [[procyanidin]]s and [[prodelphinidin]]s oligomers.<ref name="M2009">{{cite journal |author1=Mattivi F. |author2=Vrhovsek U. |author3=Masuero D. |author4=Trainotti D. |title=Differences in the amount and structure of extractable skin and seed tannins amongst red grape cultivars |journal=Australian Journal of Grape and Wine Research |volume=15 |pages=27–35 |year=2009 |doi=10.1111/j.1755-0238.2008.00027.x}}</ref> The tannins are formed by [[enzymes]] during metabolic processes of the grapevine. The amount of tannins found naturally in grapes varies depending on the variety with [[Cabernet Sauvignon]], [[Nebbiolo]], [[Syrah]] and [[Tannat]] being 4 of the most tannic grape varieties. The reaction of tannins and anthocyanins with the phenolic compound [[catechin]]s creates another class of tannins known as '''pigmented tannins''' which influence the color of red wine.<ref name="cat.inist.fr">Compositional investigation of pigmented tannin. Kennedy James A. and Hayasaka Yoji, A.C.S. symposium series, 2004, vol. 886, pp. 247-264, {{INIST|16184447}}</ref> Commercial preparations of tannins, known as ''enological tannins'', made from [[oak wood]], [[grape]] seed and skin, plant [[gall]], [[chestnut]], [[quebracho tannin|quebracho]], [[Uncaria gambir|gambier]]<ref name="Luz Sanz M. 2008, pp. 778-783">Identification of the origin of commercial enological tannins by the analysis of monosaccharides and polyalcohols. Luz Sanz M., Martinez-Castro Isabel and Moreno-Arribas M. Victoria, ''Food chemistry'', 2008, vol. 111, no3, pp. 778-783, {{INIST|20520307}}</ref> and [[myrobalan]] fruits,<ref name="ajevonline.org">{{cite journal | last1 = Marie-hélène | first1 = Salagoity-Auguste | last2 = Tricard | first2 = Christian | last3 = Marsal | first3 = Frédéric | last4 = Sudraud | first4 = Pierre | year = 1986 | title = Preliminary Investigation for the Differentiation of Enological Tannins According to Botanical Origin: Determination of Gallic Acid and Its Derivatives | url = http://www.ajevonline.org/cgi/content/abstract/37/4/301 | journal = Am. J. Enol. Vitic | volume = 37 | issue = 4| pages = 301–303 | doi = 10.5344/ajev.1986.37.4.301 | s2cid = 88027174 }}</ref> can be added at different stages of the wine production to improve color durability. The tannins derived from oak influence are known as "hydrolysable tannins" being created from the [[ellagic (acid)|ellagic]] and [[gallic acid]] found in the wood.<ref name="Oxford p 680"/> |
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[[File:Mthomebrew maceration.JPG|left|thumb|250px|Fermenting with the stem, seeds and skin will increase the tannin content of the wine.]] |
[[File:Mthomebrew maceration.JPG|left|thumb|250px|Fermenting with the stem, seeds and skin will increase the tannin content of the wine.]] |
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In the vineyards, there is also a growing distinction being made between "ripe" and "unripe" tannins present in the grape. This "[[physiological ripeness]]", which is roughly determined by tasting the grapes off the vines, is being used along with sugar levels as a determination of when to [[harvest (wine)|harvest]]. The idea is that "riper" tannins will taste softer but still impart some of the texture components found favorable in wine. In winemaking, the amount of the time that the must spends in contact with the grape skins, stems and seeds will influence the amount of tannins that are present in the wine with wines subjected to longer maceration period having more tannin extract. Following harvest, stems are normally picked out and discarded prior to fermentation but some winemakers may intentionally leave in a few stems for varieties low in tannins (like Pinot noir) in order to increase the tannic extract in the wine. If there is an excess in the amount of tannins in the wine, winemakers can use various [[fining (wine)|fining]] agents like [[albumin]], [[casein]] and [[gelatin]] that can bind to tannins molecule and [[precipitate]] them out as sediments. As a wine ages, tannins will form long polymerized chains which come across to a taster as "softer" and less tannic. This process can be accelerated by exposing the wine to [[oxygen]], which oxidize tannins to quinone-like compounds that are polymerization-prone. The winemaking technique of [[micro-oxygenation]] and [[decanting wine]] use oxygen to partially mimic the effect of aging on tannins.<ref name="Oxford |
In the vineyards, there is also a growing distinction being made between "ripe" and "unripe" tannins present in the grape. This "[[physiological ripeness]]", which is roughly determined by tasting the grapes off the vines, is being used along with sugar levels as a determination of when to [[harvest (wine)|harvest]]. The idea is that "riper" tannins will taste softer but still impart some of the texture components found favorable in wine. In winemaking, the amount of the time that the must spends in contact with the grape skins, stems and seeds will influence the amount of tannins that are present in the wine with wines subjected to longer maceration period having more tannin extract. Following harvest, stems are normally picked out and discarded prior to fermentation but some winemakers may intentionally leave in a few stems for varieties low in tannins (like Pinot noir) in order to increase the tannic extract in the wine. If there is an excess in the amount of tannins in the wine, winemakers can use various [[fining (wine)|fining]] agents like [[albumin]], [[casein]] and [[gelatin]] that can bind to tannins molecule and [[precipitate]] them out as sediments. As a wine ages, tannins will form long polymerized chains which come across to a taster as "softer" and less tannic. This process can be accelerated by exposing the wine to [[oxygen]], which oxidize tannins to quinone-like compounds that are polymerization-prone. The winemaking technique of [[micro-oxygenation]] and [[decanting wine]] use oxygen to partially mimic the effect of aging on tannins.<ref name="Oxford p 680"/> |
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A study in wine production and consumption has shown that tannins, in the form of [[proanthocyanidin]]s, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in proanthocyanidins, and that these regions also produce populations with longer life spans.<ref>{{cite journal |author=Corder R |title=Oenology: red wine procyanidins and vascular health |journal=Nature |volume=444 |issue=7119 |pages=566 |date=November 2006 |pmid=17136085 |doi=10.1038/444566a |name-list- |
A study in wine production and consumption has shown that tannins, in the form of [[proanthocyanidin]]s, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in proanthocyanidins, and that these regions also produce populations with longer life spans.<ref>{{cite journal |author=Corder R |title=Oenology: red wine procyanidins and vascular health |journal=Nature |volume=444 |issue=7119 |pages=566 |date=November 2006 |pmid=17136085 |doi=10.1038/444566a |name-list-style=vanc|author2=Mullen W |author3=Khan NQ |display-authors=3 |last4=Marks |first4=S. C. |last5=Wood |first5=E. G. |last6=Carrier |first6=M. J. |last7=Crozier |first7=A.|bibcode=2006Natur.444..566C |s2cid=4303406 |doi-access=free }}</ref> |
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Reactions of tannins with the phenolic compound [[anthocyanidin]]s creates another class of tannins known as ''pigmented tannins'' which influences the color of red wine.<ref name="cat.inist.fr"/> |
Reactions of tannins with the phenolic compound [[anthocyanidin]]s creates another class of tannins known as ''pigmented tannins'' which influences the color of red wine.<ref name="cat.inist.fr"/> |
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Tannins are a natural preservative in wine. Un-aged wines with high tannin content can be less palatable than wines with a lower level of tannins. Tannins can be described as leaving a dry and puckered feeling with a "furriness" in the mouth that can be compared to a stewed tea, which is also very tannic. This effect is particularly profound when drinking tannic wines without the benefit of food. |
Tannins are a natural preservative in wine. Un-aged wines with high tannin content can be less palatable than wines with a lower level of tannins. Tannins can be described as leaving a dry and puckered feeling with a "furriness" in the mouth that can be compared to a stewed tea, which is also very tannic. This effect is particularly profound when drinking tannic wines without the benefit of food. |
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Many [[Oenophile|wine lovers]] see natural tannins (found particularly in varietals such as [[Cabernet Sauvignon]] and often accentuated by heavy [[oak]] barrel aging) as a sign of potential longevity and [[ageability (wine)|ageability]]. Tannins impart a mouth-puckering astringency when the wine is young but "resolve" (through a chemical process called [[polymerization]]) into delicious and complex elements of "bottle [[bouquet (wine)|bouquet]]" when the wine is cellared under appropriate temperature conditions, preferably in the range of a constant {{convert|55|to|60|F|C}}.<ref> |
Many [[Oenophile|wine lovers]] see natural tannins (found particularly in varietals such as [[Cabernet Sauvignon]] and often accentuated by heavy [[oak]] barrel aging) as a sign of potential longevity and [[ageability (wine)|ageability]]. Tannins impart a mouth-puckering astringency when the wine is young but "resolve" (through a chemical process called [[polymerization]]) into delicious and complex elements of "bottle [[bouquet (wine)|bouquet]]" when the wine is cellared under appropriate temperature conditions, preferably in the range of a constant {{convert|55|to|60|F|C}}.<ref>{{Cite web|url=http://www.wine-lovers-page.com/cgi-bin/lexicon/gd.cgi?w=415|archiveurl=https://web.archive.org/web/20110718062228/http://www.wine-lovers-page.com/cgi-bin/lexicon/gd.cgi?w=415|url-status=dead|title=Wine Lovers Page - Wine Lexicon: Tannic, tannis|archivedate=July 18, 2011}}</ref> Such wines mellow and improve with age with the tannic "backbone" helping the wine survive for as long as 40 years or more.<ref>{{cite news |url=https://www.vinology.com/what-are-tannins/ |title=What are Tannins in Wine? |first = Keith S|last = Wallace|date = 2005|website = Wine School}}</ref> In many regions (such as in [[Bordeaux]]), tannic grapes such as [[Cabernet Sauvignon]] are blended with lower-tannin grapes such as [[Merlot]] or [[Cabernet Franc]], diluting the tannic characteristics. White wines and wines that are vinified to be drunk young (for examples, see [[nouveau wine]]s) typically have lower tannin levels. |
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=== Other flavonoids === |
=== Other flavonoids === |
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'''[[Flavan-3-ol]]s (catechins)''' are flavonoids that contribute to the construction of various tannins and contribute to the perception of bitterness in wine. They are found in highest concentrations in grape seeds but are also in the skin and stems. Catechins play a role in the [[microbial]] defense of the grape berry, being produced in higher concentrations by the grape vines when it is being attacked by [[grape disease]]s such as [[downy mildew]]. Because of that grape vines in cool, damp climates produce catechins at high levels than vines in dry, hot climates. Together with anthocyanins and tannins they increase the stability of a wines color-meaning that a wine will be able to maintain its coloring for a longer period of time. The amount of catechins present varies among grape varieties with varietals like Pinot noir having high concentrations while [[Merlot]] and especially Syrah have very low levels.<ref name="M2009"/> |
'''[[Flavan-3-ol]]s (catechins)''' are flavonoids that contribute to the construction of various tannins and contribute to the perception of bitterness in wine. They are found in highest concentrations in grape seeds but are also in the skin and stems. Catechins play a role in the [[microbial]] defense of the grape berry, being produced in higher concentrations by the grape vines when it is being attacked by [[grape disease]]s such as [[downy mildew]]. Because of that grape vines in cool, damp climates produce catechins at high levels than vines in dry, hot climates. Together with anthocyanins and tannins they increase the stability of a wines color-meaning that a wine will be able to maintain its coloring for a longer period of time. The amount of catechins present varies among grape varieties with varietals like Pinot noir having high concentrations while [[Merlot]] and especially Syrah have very low levels.<ref name="M2009"/> |
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As an antioxidant, there are some studies into the health benefits of moderate consumption of wines high in catechins.<ref name="Oxford |
As an antioxidant, there are some studies into the health benefits of moderate consumption of wines high in catechins.<ref name="Oxford p 144">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 144. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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In red grapes, the main flavonol is on average [[quercetin]], followed by [[myricetin]], [[kaempferol]], [[laricitrin]], [[isorhamnetin]], and [[syringetin]].<ref name="M2006">{{cite journal |author1=Mattivi F. |author2=Guzzon R. |author3=Vrhovsek U. |author4=Stefanini M. |author5=Velasco R. |title=Metabolite Profiling of Grape: Flavonols and Anthocyanins |journal=J Agric Food Chem |volume=54 |pages=7692–7702 |year=2006 |pmid=17002441 |doi=10.1021/jf061538c |issue=20}}</ref> In white grapes, the main flavonol is quercetin, followed by kaempferol and isorhamnetin. The delphinidin-like flavonols myricetin, laricitrin, and syringetin are missing in all white varieties, indicating that the enzyme flavonoid 3',5'-hydroxylase is not expressed in white grape varieties.<ref name="M2006"/> |
In red grapes, the main flavonol is on average [[quercetin]], followed by [[myricetin]], [[kaempferol]], [[laricitrin]], [[isorhamnetin]], and [[syringetin]].<ref name="M2006">{{cite journal |author1=Mattivi F. |author2=Guzzon R. |author3=Vrhovsek U. |author4=Stefanini M. |author5=Velasco R. |title=Metabolite Profiling of Grape: Flavonols and Anthocyanins |journal=J Agric Food Chem |volume=54 |pages=7692–7702 |year=2006 |pmid=17002441 |doi=10.1021/jf061538c |issue=20}}</ref> In white grapes, the main flavonol is quercetin, followed by kaempferol and isorhamnetin. The delphinidin-like flavonols myricetin, laricitrin, and syringetin are missing in all white varieties, indicating that the enzyme flavonoid 3',5'-hydroxylase is not expressed in white grape varieties.<ref name="M2006"/> |
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[[Myricetin]], [[laricitrin]]<ref>Flavonol profiles of Vitis vinifera red grapes and their single-cultivar wines. Castillo-Munoz Noelia, Gomez-Alonso Sergio, Garcia-Romero Esteban and Hermosin-Gutierrez Isidro, Journal of agricultural and food chemistry, 2007, vol. 55, no3, pp. 992-1002? {{INIST|18502213}}</ref> and [[syringetin]],<ref>{{cite journal | doi = 10.1002/mnfr.200800483 | volume=53 | title=Syringetin, a flavonoid derivative in grape and wine, induces human osteoblast differentiation through bone morphogenetic protein-2/extracellular signal-regulated kinase 1/2 pathway | year=2009 | journal=Molecular Nutrition & Food Research | pages=1452–1461 | last1 = Hsu | first1 = Ya-Ling | last2 = Liang | first2 = Hsin-Lin | last3 = Hung | first3 = Chih-Hsing | last4 = Kuo | first4 = Po-Lin| issue=11 | pmid=19784998 }}</ref> flavonols which are present in red grape varieties only, can be found in red wine.<ref name = act>{{cite journal |last1= Maggiolini |first1= M |last2= Recchia |first2= A G |title=The red wine phenolics piceatannol and myricetin act as agonists for estrogen receptor in human breast cancer cells |url=http://jme.endocrinology-journals.org/content/35/2/269.full |journal=[[Journal of Molecular Endocrinology]] |volume=35 |issue= 2 |pages=269–281 |doi=10.1677/jme.1.01783 |access-date=3 March 2015 |pmid=16216908 |date=October 2005|doi-access=free }}</ref> |
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=== Non-flavonoids === |
=== Non-flavonoids === |
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{{See also|Wine and health}} |
{{See also|Wine and health}} |
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==== Hydroxycinnamic acids ==== |
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[[Hydroxycinnamic acid]]s are the most important group of nonflavonoid phenols in wine. The four most |
[[Hydroxycinnamic acid]]s are the most important group of nonflavonoid phenols in wine. The four most |
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abundant ones are the [[tartaric acid]] esters [[caftaric acid|''trans''-caftaric]], ''cis''- and ''trans''-[[coutaric acid|coutaric]], and ''trans''-[[fertaric acid]]s. In wine they are present also in the free form (''trans''-[[caffeic acid|caffeic]], ''trans''-[[p-coumaric acid|p-coumaric]], and ''trans''-[[ferulic acid]]s).<ref>{{cite journal |author=Vrhovsek U. |title=Extraction of Hydroxycinnamoyltartaric Acids from Berries of Different Grape Varieties |journal=J Agric Food Chem |volume=46 |pages=4203–8 |year=1998 |doi=10.1021/jf980461s |issue=10}}</ref> |
abundant ones are the [[tartaric acid]] esters [[caftaric acid|''trans''-caftaric]], ''cis''- and ''trans''-[[coutaric acid|coutaric]], and ''trans''-[[fertaric acid]]s. In wine they are present also in the free form (''trans''-[[caffeic acid|caffeic]], ''trans''-[[p-coumaric acid|p-coumaric]], and ''trans''-[[ferulic acid]]s).<ref>{{cite journal |author=Vrhovsek U. |title=Extraction of Hydroxycinnamoyltartaric Acids from Berries of Different Grape Varieties |journal=J Agric Food Chem |volume=46 |pages=4203–8 |year=1998 |doi=10.1021/jf980461s |issue=10}}</ref> |
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''V. vinifera'' also produces [[stilbenoid]]s. |
''V. vinifera'' also produces [[stilbenoid]]s. |
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[[Resveratrol]] is found in highest concentration in the skins of wine grapes. The accumulation in ripe berries of different concentrations of both bound and free resveratrols depends on the maturity level and is highly variable according to the genotype.<ref>{{cite journal |author1=Gatto P. |author2=Vrhovsek U. |author3=Muth J. |author4=Segala C. |author5=Romualdi C. |author6=Fontana P. |author7=Pruefer D. |author8=Stefanini M. |author9=Moser C. |author10=Mattivi F. |author11=Velasco R. |title=Ripening and genotype control stilbene accumulation in healthy grapes |journal=J Agric Food Chem |volume=56 |issue=24 |pages=11773–85 |year=2008 |pmid=19032022 |doi=10.1021/jf8017707}}</ref> Both red and white wine grape varieties contain resveratrol, but more frequent skin contact and maceration leads to red wines normally having ten times more resveratrol than white wines.<ref>{{cite journal |author=Mattivi F. |title=Solid phase extraction of trans-resveratrol from wines for HPLC analysis |journal=Zeitschrift für Lebensmittel-Untersuchung und -Forschung |volume=196 |pages=522–5 |year=1993 |pmid=8328217 |doi=10.1007/BF01201331 |issue=6}}</ref> Resveratrol produced by grape vines provides defense against microbes, and production can be further artificially stimulated by [[ultraviolet radiation]]. Grapevines in cool, damp regions with higher risk of grape diseases, such as [[Bordeaux (wine)|Bordeaux]] and [[Burgundy (wine)|Burgundy]], tend to produce grapes with higher levels of resveratrol than warmer, drier wine regions such as [[California (wine)|California]] and [[Australia (wine)|Australia]]. Different grape varieties tend to have differing levels, with [[Muscadine]]s and the Pinot family having high levels while the [[Cabernet Sauvignon|Cabernet]] family has lower levels of resveratrol. In the late 20th century interest in the possible health benefits of resveratrol in wine was spurred by discussion of the [[French paradox]] involving the health of wine drinkers in France.<ref name="Oxford |
[[Resveratrol]] is found in highest concentration in the skins of wine grapes. The accumulation in ripe berries of different concentrations of both bound and free resveratrols depends on the maturity level and is highly variable according to the genotype.<ref>{{cite journal |author1=Gatto P. |author2=Vrhovsek U. |author3=Muth J. |author4=Segala C. |author5=Romualdi C. |author6=Fontana P. |author7=Pruefer D. |author8=Stefanini M. |author9=Moser C. |author10=Mattivi F. |author11=Velasco R. |title=Ripening and genotype control stilbene accumulation in healthy grapes |journal=J Agric Food Chem |volume=56 |issue=24 |pages=11773–85 |year=2008 |pmid=19032022 |doi=10.1021/jf8017707}}</ref> Both red and white wine grape varieties contain resveratrol, but more frequent skin contact and maceration leads to red wines normally having ten times more resveratrol than white wines.<ref>{{cite journal |author=Mattivi F. |title=Solid phase extraction of trans-resveratrol from wines for HPLC analysis |journal=Zeitschrift für Lebensmittel-Untersuchung und -Forschung |volume=196 |pages=522–5 |year=1993 |pmid=8328217 |doi=10.1007/BF01201331 |issue=6|s2cid=46152576 }}</ref> Resveratrol produced by grape vines provides defense against microbes, and production can be further artificially stimulated by [[ultraviolet radiation]]. Grapevines in cool, damp regions with higher risk of grape diseases, such as [[Bordeaux (wine)|Bordeaux]] and [[Burgundy (wine)|Burgundy]], tend to produce grapes with higher levels of resveratrol than warmer, drier wine regions such as [[California (wine)|California]] and [[Australia (wine)|Australia]]. Different grape varieties tend to have differing levels, with [[Muscadine]]s and the Pinot family having high levels while the [[Cabernet Sauvignon|Cabernet]] family has lower levels of resveratrol. In the late 20th century interest in the possible health benefits of resveratrol in wine was spurred by discussion of the [[French paradox]] involving the health of wine drinkers in France.<ref name="Oxford p 569">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 569. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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[[Piceatannol]] is also present in grape <ref name="B2002">{{cite journal |author1=Bavaresco L. |author2=Fregoni M. |author3=Trevisan M. |author4=Mattivi F. |author5=Vrhovsek U |author6=Falchetti R. |title=The occurrence of piceatannol in grape |journal=Vitis |volume=41 |issue=3 |pages=133–6 |year=2002}}</ref> from where it can be extracted and found in red wine.<ref name |
[[Piceatannol]] is also present in grape <ref name="B2002">{{cite journal |author1=Bavaresco L. |author2=Fregoni M. |author3=Trevisan M. |author4=Mattivi F. |author5=Vrhovsek U |author6=Falchetti R. |title=The occurrence of piceatannol in grape |journal=Vitis |volume=41 |issue=3 |pages=133–6 |year=2002}}</ref> from where it can be extracted and found in red wine.<ref name = act/> |
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==== Phenolic acids ==== |
==== Phenolic acids ==== |
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[[Vanillin]] is a phenolic [[aldehyde]] most commonly associated with the vanilla notes in wines that have been aged in oak. Trace amounts of vanillin are found naturally in grapes, but they are most prominent in the [[lignin]] structure of oak barrels. Newer barrels will impart more vanillin, with the concentration present decreasing with each subsequent usage.<ref name="Oxford |
[[Vanillin]] is a phenolic [[aldehyde]] most commonly associated with the vanilla notes in wines that have been aged in oak. Trace amounts of vanillin are found naturally in grapes, but they are most prominent in the [[lignin]] structure of oak barrels. Newer barrels will impart more vanillin, with the concentration present decreasing with each subsequent usage.<ref name="Oxford p 727">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 727. Oxford University Press 2006 {{ISBN|0-19-860990-6}}.</ref> |
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== Phenols from oak ageing == |
== Phenols from oak ageing == |
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[[File:WineBarrels 2005 SeanMcClean.jpg|right|thumb|250px|Phenolic compounds like tannins and vanillin can be extracted from aging in [[oak (wine)|oak wine barrels]].]] |
[[File:WineBarrels 2005 SeanMcClean.jpg|right|thumb|250px|Phenolic compounds like tannins and vanillin can be extracted from aging in [[oak (wine)|oak wine barrels]].]] |
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Oak barrel will add compounds such as [[vanillin]] and hydrolysable tannins ([[ellagitannin]]s). The [[hydrolyzable tannin]]s present in oak are derived from [[lignin]] structures in the wood. They help protect the wine from oxidation and [[redox|reduction]].<ref name="Oxford |
Oak barrel will add compounds such as [[vanillin]] and hydrolysable tannins ([[ellagitannin]]s). The [[hydrolyzable tannin]]s present in oak are derived from [[lignin]] structures in the wood. They help protect the wine from oxidation and [[redox|reduction]].<ref name="Oxford p 492">J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 492, Oxford University Press 2006, {{ISBN|0-19-860990-6}}.</ref> |
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[[4-Ethylphenol]] and [[4-ethylguaiacol]] are produced during ageing of red wine in oak barrels that are infected by [[brettanomyces]] .<ref>{{Cite journal|doi=10.1016/S0021-9673(00)00086-8|title=Quantitative analysis of 4-ethylphenol and 4-ethylguaiacol in red wine|year=2000|last1=Pollnitz|first1=Alan P|last2=Pardon|first2=Kevin H|last3=Sefton|first3=Mark A|journal=Journal of Chromatography A|volume=874|pages=101–9|pmid=10768504|issue=1}}</ref> |
[[4-Ethylphenol]] and [[4-ethylguaiacol]] are produced during ageing of red wine in oak barrels that are infected by [[brettanomyces]] .<ref>{{Cite journal|doi=10.1016/S0021-9673(00)00086-8|title=Quantitative analysis of 4-ethylphenol and 4-ethylguaiacol in red wine|year=2000|last1=Pollnitz|first1=Alan P|last2=Pardon|first2=Kevin H|last3=Sefton|first3=Mark A|journal=Journal of Chromatography A|volume=874|pages=101–9|pmid=10768504|issue=1}}</ref> |
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== Natural phenols and polyphenols from cork stoppers == |
== Natural phenols and polyphenols from cork stoppers == |
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[[File:EmbotelladoDeOrigen.jpg|thumb|left|Extracted cork closure inscribed with "Bottled at origin" in Spanish]] |
[[File:EmbotelladoDeOrigen.jpg|thumb|left|Extracted cork closure inscribed with "Bottled at origin" in Spanish]] |
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Low molecular weight polyphenols, as well as ellagitannins, are susceptible to be extracted from [[Cork (material)|cork stopper]]s into the wine.<ref>{{cite journal|doi=10.1007/s002170100327|title=Polyphenols susceptible to migrate from cork stoppers to wine|year=2001| |
Low molecular weight polyphenols, as well as ellagitannins, are susceptible to be extracted from [[Cork (material)|cork stopper]]s into the wine.<ref>{{cite journal|doi=10.1007/s002170100327|title=Polyphenols susceptible to migrate from cork stoppers to wine|year=2001|first1=S. |last1=Varea|first2=M.|last2=García-Vallejo|first3=E.|last3=Cadahía|last4=de Simón |first4=Fernández|journal=European Food Research and Technology |volume=213|pages=56–61|s2cid=85419949}}, {{INIST|1144008}}</ref> The identified polyphenols are gallic, [[protocatechuic acid|protocatechuic]], [[vanillic acid|vanillic]], caffeic, [[ferulic acid|ferulic]], and ellagic acids; [[protocatechuic aldehyde|protocatechuic]], [[vanillic acid|vanillic]], [[coniferyl aldehyde|coniferyl]], and [[sinapic aldehyde|sinapic]] aldehydes; the coumarins [[aesculetin]] and [[scopoletin]]; the ellagitannins are roburins [[roburin A|A]] and [[roburin E|E]], [[grandinin]], [[vescalagin]] and [[castalagin]].<ref>{{cite journal|doi=10.1021/jf970863k|title=Polyphenolic Composition of ''Quercus suber'' Cork from Different Spanish Provenances|year=1998|last1=Conde|first1=Elvira|last2=Cadahía|first2=Estrella|last3=García-Vallejo|first3=María Concepción|last4=Fernández de Simón|first4=Brígida|journal=Journal of Agricultural and Food Chemistry|volume=46|issue=8|pages=3166–3171}}</ref> |
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[[Guaiacol]] is one of the molecules responsible for the [[cork taint]] wine fault.<ref>{{cite journal|doi=10.1016/S0378-1097(03)00053-3|title=Degradation of vanillic acid and production of guaiacol by microorganisms isolated from cork samples|year=2003|last1=Alvarez- |
[[Guaiacol]] is one of the molecules responsible for the [[cork taint]] wine fault.<ref>{{cite journal |doi=10.1016/S0378-1097(03)00053-3|title=Degradation of vanillic acid and production of guaiacol by microorganisms isolated from cork samples|year=2003|last1=Alvarez-Rodríguez|first1=María Luisa|last2=Belloch|first2=Carmela|last3=Villa|first3= Mercedes|last4=Uruburu |first4=Federico|last5=Larriba|first5=Germán|last6=Coque|first6=Juan-José R|journal=FEMS Microbiology Letters|volume=220|pages= 49–55|pmid=12644227|issue=1|doi-access=free}}</ref> |
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== Phenolic content in relation with wine making techniques == |
== Phenolic content in relation with wine making techniques == |
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* [[Castavinol C3]] |
* [[Castavinol C3]] |
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* [[Castavinol C4]] |
* [[Castavinol C4]] |
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* [[Catechin]]<ref name=":0">{{Cite journal| |
* [[Catechin]]<ref name=":0">{{Cite journal|last1=Aizpurua-Olaizola|first1=Oier|last2=Ormazabal|first2=Markel|last3=Vallejo|first3=Asier|last4=Olivares|first4=Maitane|last5=Navarro|first5=Patricia|last6=Etxebarria|first6=Nestor|last7=Usobiaga|first7=Aresatz|date=2015-01-01|title=Optimization of Supercritical Fluid Consecutive Extractions of Fatty Acids and Polyphenols from Vitis Vinifera Grape Wastes|journal=Journal of Food Science|language=en|volume=80|issue=1|pages=E101–E107|doi=10.1111/1750-3841.12715|pmid=25471637|issn=1750-3841}}</ref> |
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* [[Catechin-(4,8)-malvidin-3-O-glucoside]]<ref>{{cite journal | doi = 10.1021/jp104749f | volume=114 | title=Thermodynamic and Kinetic Properties of a Red Wine Pigment: Catechin-(4,8)-malvidin-3- O -glucoside | year=2010 | journal=The Journal of Physical Chemistry B | pages=13487–13496 | last1 = Nave | first1 = Frederico}}</ref> |
* [[Catechin-(4,8)-malvidin-3-O-glucoside]]<ref>{{cite journal | doi = 10.1021/jp104749f | volume=114 | title=Thermodynamic and Kinetic Properties of a Red Wine Pigment: Catechin-(4,8)-malvidin-3- O -glucoside | year=2010 | journal=The Journal of Physical Chemistry B | pages=13487–13496 | last1 = Nave | first1 = Frederico| issue=42 | pmid=20925351 }}</ref> |
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* [[Compound NJ2]] |
* [[Compound NJ2]] |
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* [[Coniferyl aldehyde]] |
* [[Coniferyl aldehyde]] |
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** [[procyanidin C1]] (epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin) |
** [[procyanidin C1]] (epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin) |
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** [[Procyanidin C2]] (catechin-(4α→8)-catechin-(4α→8)-catechin) |
** [[Procyanidin C2]] (catechin-(4α→8)-catechin-(4α→8)-catechin) |
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** [[procyanidin T2]] (trimer)<ref>Degradation of oligomeric procyanidins and anthocyanins in a Tinta Roriz red wine during maturation |
** [[procyanidin T2]] (trimer)<ref>{{cite journal|title = Degradation of oligomeric procyanidins and anthocyanins in a Tinta Roriz red wine during maturation|first1= C.|last1 = Dallas|first2= J.M.|last2= Ricardo-Da-Silva |first3= Olga|last3= Laureano|journal = Vitis|date= 1995| volume=34| issue=1| pages= 51–56|doi = 10.5073/vitis.1995.34.51-56 |url = https://www.researchgate.net/publication/258844471}}</ref> |
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* [[Protocatechuic acid]] |
* [[Protocatechuic acid]] |
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* [[protocatechuic aldehyde]] |
* [[protocatechuic aldehyde]] |
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== Effects == |
== Effects == |
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Polyphenol compounds may interact with [[Volatile organic compounds|volatiles]] and contribute to the aromas in wine.<ref>{{cite journal|pmid=10563952|year=1999| |
Polyphenol compounds may interact with [[Volatile organic compounds|volatiles]] and contribute to the aromas in wine.<ref>{{cite journal|pmid=10563952|year=1999|last1=Dufour|first1=C|title=Interactions between wine polyphenols and aroma substances. An insight at the molecular level|journal=Journal of Agricultural and Food Chemistry|volume=47|issue= 2|pages=678–84|last2=Bayonove|first2=C. L.|doi=10.1021/jf980314u}}</ref> Although wine polyphenols are speculated to provide [[antioxidant]] or other benefits, there is little evidence that wine polyphenols actually have any effect in humans.<ref name="Haseeb">{{cite journal | last1=Haseeb | first1=Sohaib | last2=Alexander | first2=Bryce | last3=Baranchuk | first3=Adrian | title=Wine and cardiovascular health | journal=Circulation | volume=136 | issue=15 | date=10 October 2017 | issn=0009-7322 | pmid=28993373 | doi=10.1161/circulationaha.117.030387 | pages=1434–1448| s2cid=26520546 | doi-access=free }}</ref><ref name="lpi">{{cite web|url=http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids|title=Flavonoids|publisher=Linus Pauling Institute, Micronutrient Information Center, Oregon State University|date=2015|access-date=11 June 2017}}</ref><ref name="EFSA">{{cite journal|author=EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)|title= Scientific Opinion on the substantiation of health claims related to various food(s)/food constituent(s) and protection of cells from premature aging, antioxidant activity, antioxidant content and antioxidant properties, and protection of DNA, proteins and lipids from oxidative damage pursuant to Article 13(1) of Regulation (EC) No 1924/20061|journal= EFSA Journal|year= 2010|volume= 8|issue=2|page=1489|doi=10.2903/j.efsa.2010.1489|doi-access=free}}</ref><ref>{{cite journal | author=Halliwell B | title=Dietary polyphenols: Good, bad, or indifferent for your health? |journal= Cardiovasc Res | volume=73 | issue=2 | pages=341–347 | year=2007 | doi=10.1016/j.cardiores.2006.10.004 | pmid=17141749| doi-access=free }}</ref> Limited preliminary research indicates that wine polyphenols may decrease [[platelet aggregation]], enhance [[fibrinolysis]], and increase [[HDL cholesterol]], but high-quality [[clinical trial]]s have not confirmed such effects, as of 2017.<ref name=Haseeb/> |
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== See also == |
== See also == |
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* [[Clarification and stabilization of wine]] |
* [[Clarification and stabilization of wine]] |
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* [[Grape seed extract]] |
* [[Grape seed extract]] |
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*[[Phenolic content in tea]] |
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* [[Wine chemistry]] |
* [[Wine chemistry]] |
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* [[Wine preservatives]] |
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== References == |
== References == |
The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine.[1] The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
The natural phenols are not evenly distributed within the fruit. Phenolic acids are largely present in the pulp, anthocyanins and stilbenoids in the skin, and other phenols (catechins, proanthocyanidins and flavonols) in the skin and the seeds.[2] During the growth cycle of the grapevine, sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of canopy management. The proportion of the different phenols in any one wine will therefore vary according to the type of vinification. Red wine will be richer in phenols abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols, whereas the phenols in white wine will essentially originate from the pulp, and these will be the phenolic acids together with lower amounts of catechins and stilbenes. Red wines will also have the phenols found in white wines.
Wine simple phenols are further transformed during wine aging into complex molecules formed notably by the condensation of proanthocyanidins and anthocyanins, which explains the modification in the color. Anthocyanins react with catechins, proanthocyanidins and other wine components during wine aging to form new polymeric pigments resulting in a modification of the wine color and a lower astringency.[3][4] Average total polyphenol content measured by the Folin method is 216 mg/100 ml for red wine and 32 mg/100 ml for white wine. The content of phenols in rosé wine (82 mg/100 ml) is intermediate between that in red and white wines.
Inwinemaking, the process of maceration or "skin contact" is used to increase the concentration of phenols in wine. Phenolic acids are found in the pulp or juice of the wine and can be commonly found in white wines which usually do not go through a maceration period. The process of oak aging can also introduce phenolic compounds into wine, most notably vanillin which adds vanilla aroma to wines.[5]
Most wine phenols are classified as secondary metabolites and were not thought to be active in the primary metabolism and function of the grapevine. However, there is evidence that in some plants flavonoids play a role as endogenous regulators of auxin transport.[6] They are water-soluble and are usually secreted into the vacuole of the grapevine as glycosides.
Vitis vinifera produces many phenolic compounds. There is a varietal effect on the relative composition.
In red wine, up to 90% of the wine's phenolic content falls under the classification of flavonoids. These phenols, mainly derived from the stems, seeds and skins are often leached out of the grape during the maceration period of winemaking. The amount of phenols leached is known as extraction. These compounds contribute to the astringency, color and mouthfeel of the wine. In white wines the number of flavonoids is reduced due to the lesser contact with the skins that they receive during winemaking. There is on-going study into the health benefits of wine derived from the antioxidant and chemopreventive properties of flavonoids.[7]
Within the flavonoid category is a subcategory known as flavonols, which includes the yellow pigment - quercetin. Like other flavonoids, the concentration of flavonols in the grape berries increases as they are exposed to sunlight. Wine grapes facing too much sun exposure can see an accelerated ripening period, leading to a lessened ability for the synthesis of flavonols.[8] Some viticulturalists will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques.
Anthocyanins are phenolic compounds found throughout the plant kingdom, being frequently responsible for the blue to red colors found in flowers, fruits and leaves. In wine grapes, they develop during the stage of veraison, when the skin of red wine grapes changes color from green to red to black. As the sugars in the grape increase during ripening so does the concentration of anthocyanins. An issue associated with climate change has been the accumulation of sugars within the grape accelerating rapidly and outpacing the accumulation of anthocyanins.[8] This leaves viticulturists with the choice of harvesting grapes with too high sugar content or with too low anthocyanin content. In most grapes anthocyanins are found only in the outer cell layers of the skin, leaving the grape juice inside virtually colorless. Therefore, to get color pigmentation in the wine, the fermenting must needs to be in contact with the grape skins in order for the anthocyanins to be extracted. Hence, white wine can be made from red wine grapes in the same way that many white sparkling wines are made from the red wine grapes of Pinot noir and Pinot Meunier. The exception to this is the small class of grapes known as teinturiers, such as Alicante Bouschet, which have a small amount of anthocyanins in the pulp that produces pigmented juice.[9]
There are several types of anthocyanins (as the glycoside) found in wine grapes which are responsible for the vast range of coloring from ruby red through to dark black found in wine grapes. Ampelographers can use this observation to assist in the identification of different grape varieties. The European vine family Vitis vinifera is characterized by anthocyanins that are composed of only one molecule of glucose while non-vinifera vines such as hybrids and the American Vitis labrusca will have anthocyanins with two molecules. This phenomenon is due to a double mutation in the anthocyanin 5-O-glucosyltransferase gene of V. vinifera.[10] In the mid-20th century, French ampelographers used this knowledge to test the various vine varieties throughout France to identify which vineyards still contained non-vinifera plantings.[9]
Red-berried Pinot grape varieties are also known to not synthesize para-coumaroylatedoracetylated anthocyanins as other varieties do.[11]
The color variation in the finished red wine is partly derived from the ionization of anthocyanin pigments caused by the acidity of the wine. In this case, the three types of anthocyanin pigments are red, blue and colorless with the concentration of those various pigments dictating the color of the wine. A wine with low pH (and such greater acidity) will have a higher occurrence of ionized anthocyanins which will increase the amount of bright red pigments. Wines with a higher pH will have a higher concentration of blue and colorless pigments. As the wine ages, anthocyanins will react with other acids and compounds in wines such as tannins, pyruvic acid and acetaldehyde which will change the color of the wine, causing it to develop more "brick red" hues. These molecules will link up to create polymers that eventually exceed their solubility and become sediment at the bottom of wine bottles.[9] Pyranoanthocyanins are chemical compounds formed in red winesbyyeast during fermentation processes[12] or during controlled oxygenation processes[13] during the aging of wine.[14]
Tannins refer to the diverse group of chemical compounds in wine that can affect the color, aging ability and texture of the wine. While tannins cannot be smelled or tasted, they can be perceived during wine tasting by the tactile sensation of astringency and sense of bitterness that they can leave in the mouth. This is due to the tendency of tannins to react with proteins, such as the ones found in saliva.[15]Infood and wine pairing, foods that are high in proteins (such as red meat) are often paired with tannic wines to minimize the astringency of tannins. However, many wine drinkers find the perception of tannins to be a positive trait—especially as it relates to mouthfeel. The management of tannins in the winemaking process is a key component in the resulting quality.[16]
Tannins are found in the skin, stems, and seeds of wine grapes but can also be introduced to the wine through the use of oak barrels and chips or with the addition of tannin powder. The natural tannins found in grapes are known as proanthocyanidins due to their ability to release red anthocyanin pigments when they are heated in an acidic solution. Grape extracts are mainly rich in monomers and small oligomers (mean degree of polymerization <8). Grape seed extracts contain three monomers (catechin, epicatechin and epicatechin gallate) and procyanidin oligomers. Grape skin extracts contain four monomers (catechin, epicatechin, gallocatechin and epigallocatechin), as well as procyanidins and prodelphinidins oligomers.[17] The tannins are formed by enzymes during metabolic processes of the grapevine. The amount of tannins found naturally in grapes varies depending on the variety with Cabernet Sauvignon, Nebbiolo, Syrah and Tannat being 4 of the most tannic grape varieties. The reaction of tannins and anthocyanins with the phenolic compound catechins creates another class of tannins known as pigmented tannins which influence the color of red wine.[18] Commercial preparations of tannins, known as enological tannins, made from oak wood, grape seed and skin, plant gall, chestnut, quebracho, gambier[19] and myrobalan fruits,[20] can be added at different stages of the wine production to improve color durability. The tannins derived from oak influence are known as "hydrolysable tannins" being created from the ellagic and gallic acid found in the wood.[16]
In the vineyards, there is also a growing distinction being made between "ripe" and "unripe" tannins present in the grape. This "physiological ripeness", which is roughly determined by tasting the grapes off the vines, is being used along with sugar levels as a determination of when to harvest. The idea is that "riper" tannins will taste softer but still impart some of the texture components found favorable in wine. In winemaking, the amount of the time that the must spends in contact with the grape skins, stems and seeds will influence the amount of tannins that are present in the wine with wines subjected to longer maceration period having more tannin extract. Following harvest, stems are normally picked out and discarded prior to fermentation but some winemakers may intentionally leave in a few stems for varieties low in tannins (like Pinot noir) in order to increase the tannic extract in the wine. If there is an excess in the amount of tannins in the wine, winemakers can use various fining agents like albumin, casein and gelatin that can bind to tannins molecule and precipitate them out as sediments. As a wine ages, tannins will form long polymerized chains which come across to a taster as "softer" and less tannic. This process can be accelerated by exposing the wine to oxygen, which oxidize tannins to quinone-like compounds that are polymerization-prone. The winemaking technique of micro-oxygenation and decanting wine use oxygen to partially mimic the effect of aging on tannins.[16]
A study in wine production and consumption has shown that tannins, in the form of proanthocyanidins, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in proanthocyanidins, and that these regions also produce populations with longer life spans.[21]
Reactions of tannins with the phenolic compound anthocyanidins creates another class of tannins known as pigmented tannins which influences the color of red wine.[18]
Commercial preparations of tannins, known as enological tannins, made from oak wood, grape seed and skin, plant gall, chestnut, quebracho, gambier[19] and myrobalan fruits,[20] can be added at different stages of the wine production to improve color durability.
Tannins are a natural preservative in wine. Un-aged wines with high tannin content can be less palatable than wines with a lower level of tannins. Tannins can be described as leaving a dry and puckered feeling with a "furriness" in the mouth that can be compared to a stewed tea, which is also very tannic. This effect is particularly profound when drinking tannic wines without the benefit of food.
Many wine lovers see natural tannins (found particularly in varietals such as Cabernet Sauvignon and often accentuated by heavy oak barrel aging) as a sign of potential longevity and ageability. Tannins impart a mouth-puckering astringency when the wine is young but "resolve" (through a chemical process called polymerization) into delicious and complex elements of "bottle bouquet" when the wine is cellared under appropriate temperature conditions, preferably in the range of a constant 55 to 60 °F (13 to 16 °C).[22] Such wines mellow and improve with age with the tannic "backbone" helping the wine survive for as long as 40 years or more.[23] In many regions (such as in Bordeaux), tannic grapes such as Cabernet Sauvignon are blended with lower-tannin grapes such as MerlotorCabernet Franc, diluting the tannic characteristics. White wines and wines that are vinified to be drunk young (for examples, see nouveau wines) typically have lower tannin levels.
Flavan-3-ols (catechins) are flavonoids that contribute to the construction of various tannins and contribute to the perception of bitterness in wine. They are found in highest concentrations in grape seeds but are also in the skin and stems. Catechins play a role in the microbial defense of the grape berry, being produced in higher concentrations by the grape vines when it is being attacked by grape diseases such as downy mildew. Because of that grape vines in cool, damp climates produce catechins at high levels than vines in dry, hot climates. Together with anthocyanins and tannins they increase the stability of a wines color-meaning that a wine will be able to maintain its coloring for a longer period of time. The amount of catechins present varies among grape varieties with varietals like Pinot noir having high concentrations while Merlot and especially Syrah have very low levels.[17] As an antioxidant, there are some studies into the health benefits of moderate consumption of wines high in catechins.[24]
In red grapes, the main flavonol is on average quercetin, followed by myricetin, kaempferol, laricitrin, isorhamnetin, and syringetin.[25] In white grapes, the main flavonol is quercetin, followed by kaempferol and isorhamnetin. The delphinidin-like flavonols myricetin, laricitrin, and syringetin are missing in all white varieties, indicating that the enzyme flavonoid 3',5'-hydroxylase is not expressed in white grape varieties.[25]
Myricetin, laricitrin[26] and syringetin,[27] flavonols which are present in red grape varieties only, can be found in red wine.[28]
Hydroxycinnamic acids are the most important group of nonflavonoid phenols in wine. The four most abundant ones are the tartaric acid esters trans-caftaric, cis- and trans-coutaric, and trans-fertaric acids. In wine they are present also in the free form (trans-caffeic, trans-p-coumaric, and trans-ferulic acids).[29]
V. vinifera also produces stilbenoids.
Resveratrol is found in highest concentration in the skins of wine grapes. The accumulation in ripe berries of different concentrations of both bound and free resveratrols depends on the maturity level and is highly variable according to the genotype.[30] Both red and white wine grape varieties contain resveratrol, but more frequent skin contact and maceration leads to red wines normally having ten times more resveratrol than white wines.[31] Resveratrol produced by grape vines provides defense against microbes, and production can be further artificially stimulated by ultraviolet radiation. Grapevines in cool, damp regions with higher risk of grape diseases, such as Bordeaux and Burgundy, tend to produce grapes with higher levels of resveratrol than warmer, drier wine regions such as California and Australia. Different grape varieties tend to have differing levels, with Muscadines and the Pinot family having high levels while the Cabernet family has lower levels of resveratrol. In the late 20th century interest in the possible health benefits of resveratrol in wine was spurred by discussion of the French paradox involving the health of wine drinkers in France.[32]
Piceatannol is also present in grape [33] from where it can be extracted and found in red wine.[28]
Vanillin is a phenolic aldehyde most commonly associated with the vanilla notes in wines that have been aged in oak. Trace amounts of vanillin are found naturally in grapes, but they are most prominent in the lignin structure of oak barrels. Newer barrels will impart more vanillin, with the concentration present decreasing with each subsequent usage.[34]
Oak barrel will add compounds such as vanillin and hydrolysable tannins (ellagitannins). The hydrolyzable tannins present in oak are derived from lignin structures in the wood. They help protect the wine from oxidation and reduction.[35]
4-Ethylphenol and 4-ethylguaiacol are produced during ageing of red wine in oak barrels that are infected by brettanomyces .[36]
Low molecular weight polyphenols, as well as ellagitannins, are susceptible to be extracted from cork stoppers into the wine.[37] The identified polyphenols are gallic, protocatechuic, vanillic, caffeic, ferulic, and ellagic acids; protocatechuic, vanillic, coniferyl, and sinapic aldehydes; the coumarins aesculetin and scopoletin; the ellagitannins are roburins A and E, grandinin, vescalagin and castalagin.[38]
Guaiacol is one of the molecules responsible for the cork taint wine fault.[39]
Flash release is a technique used in wine pressing.[40] The technique allows for a better extraction of phenolic compounds.[41]
The exposure of wine to oxygen in limited quantities affects phenolic content.[42]
Depending on the methods of production, wine type, grape varieties, ageing processes, the following phenolics can be found in wine. The list, sorted in alphabetical order of common names, is not exhaustive.
Polyphenol compounds may interact with volatiles and contribute to the aromas in wine.[49] Although wine polyphenols are speculated to provide antioxidant or other benefits, there is little evidence that wine polyphenols actually have any effect in humans.[50][51][52][53] Limited preliminary research indicates that wine polyphenols may decrease platelet aggregation, enhance fibrinolysis, and increase HDL cholesterol, but high-quality clinical trials have not confirmed such effects, as of 2017.[50]