The phenolic content in wine refers to the phenolic compounds— natural phenol and

polyphenol Polyphenols () are a large family of naturally occurring organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include flavonoids, tannic acid, and ellagitannin, some of ...

s—in

wine Wine is an alcoholic drink typically made from fermented grapes. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide, releasing heat in the process. Different varieties of grapes and strains of yeasts are m ...

, which include a large group of several hundred

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

s that affect the

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

and

mouthfeel Mouthfeel refers to the physical sensations in the mouth caused by food or drink, making it distinct from taste. It is a fundamental sensory attribute which, along with taste and smell, determines the overall flavor of a food item. Mouthfeel ...

of wine. These compounds include

phenolic acid Phenolic acids or phenolcarboxylic acids are types of aromatic acid compounds. Included in that class are substances containing a phenolic ring and an organic carboxylic acid function (C6-C1 skeleton). Two important naturally occurring types of ...

stilbenoid Stilbenoids are hydroxylated derivatives of stilbene. They have a C6–C2–C6 structure. In biochemical terms, they belong to the family of phenylpropanoids and share most of their biosynthesis pathway with chalcones. Most stilbenoids are prod ...

flavonol Flavonols are a class of flavonoids that have the 3-hydroxyflavone backbone (IUPAC name : 3-hydroxy-2-phenylchromen-4-one). Their diversity stems from the different positions of the phenolic -OH groups. They are distinct from flavanols (with " ...

dihydroflavonol The flavanonols (with two "o"s a.k.a. 3-hydroxyflavanone or 2,3-dihydroflavonol) are a class of flavonoids that use the 3-hydroxy-2,3-dihydro-2-phenylchromen-4-one (IUPAC name) backbone. Some examples include: * Taxifolin (or Dihydroquercetin) * ...

anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...

flavanol Flavan-3-ols (sometimes referred to as flavanols) are a subgroup of flavonoids. They are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2''H''-chromen-3-ol skeleton. Flavan-3-ols are structurally diverse and include a range of com ...

monomers (

catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tannic ...

s) and

polymers (

proanthocyanidin Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More compl ...

s). This large group of natural phenols can be broadly separated into two categories,

flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s and non-flavonoids. Flavonoids include the

s and

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'', ...

s which contribute to the color and mouthfeel of the wine. The non-flavonoids include the

s such as resveratrol and

s such as benzoic, caffeic and cinnamic acids.

Origin of the phenolic compounds

The natural phenols are not evenly distributed within the fruit. Phenolic acids are largely present in the pulp,

s and

s in the skin, and other phenols (

s and

s) in the skin and the seeds. During the

growth cycle of the grapevine The annual growth cycle of grapevines is the process that takes place in the vineyard each year, beginning with bud break in the spring and culminating in leaf fall in autumn followed by winter dormancy. From a winemaking perspective, each step ...

, sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of

canopy management In viticulture, the canopy of a grapevine includes the parts of the vine visible aboveground - the trunk, cordon, stems, leaves, flowers, and fruit. The canopy plays a key role in light energy capture via photosynthesis, water use as regulated ...

. The proportion of the different phenols in any one wine will therefore vary according to the type of

vinification Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and w ...

Red wine Red wine is a type of wine made from dark-colored grape varieties. The color of the wine can range from intense violet, typical of young wines, through to brick red for mature wines and brown for older red wines. The juice from most purple grap ...

will be richer in phenols abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols, whereas the phenols in

white wine White wine is a wine that is Fermentation in winemaking, fermented without skin contact. The wine color, colour can be straw-yellow, yellow-green, or yellow-gold. It is produced by the alcoholic fermentation of the non-coloured Juice vesicles, ...

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 The aging of wine is potentially able to improve the quality of wine. This distinguishes wine from most other consumable goods. While wine is perishable and capable of deteriorating, complex chemical reactions involving a wine's sugars, acids and ...

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. 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. In

winemaking Winemaking or vinification is the production of wine, starting with the selection of the fruit, its fermentation into alcohol, and the bottling of the finished liquid. The history of wine-making stretches over millennia. The science of wine and ...

, 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 Oak is used in winemaking to vary the color, flavor, tannin profile and texture of wine. It can be introduced in the form of a barrel during the fermentation or aging periods, or as free-floating chips or staves added to wine fermented in a v ...

can also introduce phenolic compounds into wine, most notably

vanillin Vanillin is an organic compound with the molecular formula . It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now used ...

which adds

vanilla Vanilla is a spice derived from orchids of the genus ''Vanilla (genus), Vanilla'', primarily obtained from pods of the Mexican species, flat-leaved vanilla (''Vanilla planifolia, V. planifolia''). Pollination is required to make the p ...

aroma An odor (American English) or odour ( Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their se ...

to wines.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, pp 517-518. Oxford University Press 2006 . Most wine phenols are classified as

secondary metabolite Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the norm ...

s and were not thought to be active in the primary

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

and function of the grapevine. However, there is evidence that in some plants

s play a role as endogenous regulators of auxin transport. They are

water-soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

and are usually secreted into the

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

of the grapevine as glycosides.

Grape polyphenols

Vitis vinifera ''Vitis vinifera'', the common grape vine, is a species of flowering plant, native to the Mediterranean region, Central Europe, and southwestern Asia, from Morocco and Portugal north to southern Germany and east to northern Iran. There are curre ...

'' produces many phenolic compounds. There is a varietal effect on the relative composition.

Flavonoids

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 Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...

and

chemopreventive Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemotherap ...

properties of flavonoids.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, pp. 273-274. Oxford University Press 2006 .

Flavonols

Within the flavonoid category is a subcategory known as

s, which includes the yellow

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

quercetin Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds, and grains; capers, red onions, and kale are common foods containing appreciable amounts of it. It has a bitter flavor ...

. 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. Some

viticulturalist Viticulture (from the Latin word for ''vine'') or winegrowing (wine growing) is the cultivation and harvesting of grapes. It is a branch of the science of horticulture. While the native territory of ''Vitis vinifera'', the common grape vine, ran ...

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.

Anthocyanins

Anthocyanins are phenolic compounds found throughout the

plant kingdom Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...

, being frequently responsible for the blue to red colors found in

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...

s and

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

. In wine grapes, they develop during the stage of ''

veraison In viticulture, veraison (french: véraison, ) is the onset of the ripening of the grapes. The official definition of ''veraison'' is "change of color of the grape berries". Veraison represents the transition from berry growth to berry ripening, ...

,'' when the skin of red wine grapes changes color from green to red to black. As the sugars in the grape increase during

ripening Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green, and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity level does not make th ...

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. 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 Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

must Must (from the Latin ''vinum mustum'', "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of t ...

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 Sparkling wine is a wine with significant levels of carbon dioxide in it, making it fizzy. While the phrase commonly refers to champagne, European Union countries legally reserve that term for products exclusively produced in the Champagne regi ...

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 Teinturier grapes are grapes whose flesh and juice is red in colour due to anthocyanin pigments accumulating within the pulp of the grape berry itself. In most cases, anthocyanin pigments are confined to the outer skin tissue only, and the squee ...

s, such as

Alicante Bouschet Alicante Bouschet or Alicante Henri Bouschet is a wine grape variety that has been widely cultivated since 1866. It is a cross of Petit Bouschet (itself a cross of the very old variety Teinturier du Cher and Aramon) and Grenache.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 24. Oxford University Press 2006 . There are several types of anthocyanins (as the

glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...

) 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 Ampelography ( ἄμπελος, "vine" + γράφος, "writing") is the field of botany concerned with the identification and classification of grapevines, ''Vitis'' spp. Traditionally this has been done by comparing the shape and colour of the ...

s can use this observation to assist in the identification of different

grape varieties This list of grape varieties includes cultivated grapes, whether used for wine, or eating as a table grape, fresh or dried (raisin, currant, sultana). For a complete list of all grape species including those unimportant to agriculture, see Viti ...

. The European vine family ''

'' is characterized by anthocyanins that are composed of only one molecule of

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

while non-''vinifera'' vines such as hybrids and the American ''

Vitis labrusca ''Vitis labrusca'', the fox grape, is a species of grapevines belonging to the ''Vitis'' genus in the flowering plant family Vitaceae. The vines are native to eastern North America and are the source of many grape cultivars, including Catawba, C ...

'' will have anthocyanins with two molecules. This phenomenon is due to a double mutation in the anthocyanin 5-O-glucosyltransferase gene of ''V. vinifera''. 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. Red-berried Pinot grape varieties are also known to not synthesize para-coumaroylated or

acetylated anthocyanin : In organic chemistry, acetylation is an organic esterification reaction with acetic acid. It introduces an acetyl group into a chemical compound. Such compounds are termed ''acetate esters'' or simply '' acetates''. Deacetylation is the oppo ...

s as other varieties do. Tempranillowine

The color variation in the finished red wine is partly derived from the

ionization Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...

of anthocyanin pigments caused by the

acidity In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

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

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

s that eventually exceed their

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

and become sediment at the bottom of wine bottles. Pyranoanthocyanins are chemical compounds formed in red

s by

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitut ...

during

fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

processes or during controlled oxygenation processes during the

aging of wine The aging of wine is potentially able to improve the quality of wine. This distinguishes wine from most other consumable goods. While wine is perishable and capable of deteriorating, complex chemical reactions involving a wine's sugars, acids an ...

Tannins

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 Wine tasting is the sensory examination and evaluation of wine. While the practice of wine tasting is as ancient as its production, a more formalized methodology has slowly become established from the 14th century onward. Modern, professional w ...

by the

tactile Tactile may refer to: * Tactile, related to the sense of touch * Haptics (disambiguation) * Tactile (device), a text-to-braille translation device See also * Tangibility, in law * Somatosensory system, where sensations are processed * CD96 CD ...

drying sensation and sense of bitterness that they can leave in the mouth. This is due to the tendency of tannins to react with

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s, such as the ones found in

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...

. In

food and wine pairing Wine and food matching is the process of pairing food dishes with wine to enhance the dining experience. In many cultures, wine has had a long history of being a staple at the dinner table and in some ways both the winemaking and culinary traditi ...

, foods that are high in proteins (such as

red meat In gastronomy, red meat is commonly red when raw and a dark color after it is cooked, in contrast to white meat, which is pale in color before and after cooking. In culinary terms, only flesh from mammals or fowl (not fish) is classified as ...

) 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.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 680. Oxford University Press 2006 . 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

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 Procyanidins are members of the proanthocyanidin (or condensed tannins) class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions. See the ...

s and

prodelphinidin Prodelphinidin is a name for the polymeric tannins composed of gallocatechin. It yields delphinidin during depolymerisation under oxidative conditions. Natural occurrences Prodelphinidins are one of the two sorts of tannins in grape (the other ...

s oligomers. The tannins are formed by

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

during metabolic processes of the grapevine. The amount of tannins found naturally in grapes varies depending on the variety with

Cabernet Sauvignon Cabernet Sauvignon () is one of the world's most widely recognized red wine grape varieties. It is grown in nearly every major wine producing country among a diverse spectrum of climates from Australia and British Columbia, Canada to Lebanon' ...

Nebbiolo Nebbiolo (, ; pms, nebieul ) is an Italian red wine grape variety predominantly associated with its native Piedmont region, where it makes the '' Denominazione di Origine Controllata e Garantita'' (DOCG) wines of Barolo, Barbaresco, Roero ...

Syrah Syrah (), also known as Shiraz, is a dark-skinned grape variety grown throughout the world and used primarily to produce red wine. In 1999, Syrah was found to be the offspring of two obscure grapes from southeastern France, Dureza and Mondeuse B ...

and

Tannat Tannat is a red wine grape, historically grown in South West France in the Madiran AOC, and is now one of the most prominent grapes in Uruguay, where it is considered the "national grape". Tannat is also grown in Argentina, Australia, Brazi ...

being 4 of the most tannic grape varieties. The reaction of tannins and anthocyanins with the phenolic compound

s creates another class of tannins known as pigmented tannins which influence the color of red wine.Compositional investigation of pigmented tannin. Kennedy James A. and Hayasaka Yoji, A.C.S. symposium series, 2004, vol. 886, pp. 247-264, Commercial preparations of tannins, known as ''enological tannins'', made from

oak wood An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began perhaps 8,000 years ago, ...

seed and skin, plant gall,

chestnut The chestnuts are the deciduous trees and shrubs in the genus ''Castanea'', in the beech family Fagaceae. They are native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce. The unrelat ...

, quebracho, gambierIdentification 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, and myrobalan fruits, 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 Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. I ...

found in the wood. Mthomebrew maceration

In the vineyards, there is also a growing distinction being made between "ripe" and "unripe" tannins present in the grape. This "

physiological ripeness In viticulture, ripeness is the completion of the ripening process of wine grapes on the vine which signals the beginning of harvest. What exactly constitutes ripeness will vary depending on what style of wine is being produced ( sparkling, still, ...

", 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 Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ...

casein Casein ( , from Latin ''caseus'' "cheese") is a family of related phosphoproteins ( αS1, aS2, β, κ) that are commonly found in mammalian milk, comprising about 80% of the proteins in cow's milk and between 20% and 60% of the proteins in hum ...

and gelatin that can bind to tannins molecule and

precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...

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 Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

, which oxidize tannins to quinone-like compounds that are polymerization-prone. The winemaking technique of

micro-oxygenation Micro-oxygenation is a process used in winemaking to introduce oxygen into wine in a controlled manner. Developed in 1991 by Patrick DuCournau, working with the exceptionally tannic grape Tannat in Madiran, the process gained usage in modern win ...

and decanting wine use oxygen to partially mimic the effect of aging on tannins. A study in wine production and consumption has shown that tannins, in the form of

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. Reactions of tannins with the phenolic compound

anthocyanidin Anthocyanidins are common plant pigments, the sugar-free counterparts of anthocyanins. They are based on the flavylium cation, an oxonium ion, with various groups substituted for its hydrogen atoms. They generally change color from red through ...

s creates another class of tannins known as ''pigmented tannins'' which influences the color of red wine.

= Addition of enological tannins

= Commercial preparations of tannins, known as ''enological tannins'', made from

seed and skin, plant gall,

, quebracho, gambier and myrobalan fruits, can be added at different stages of the wine production to improve color durability.

= Effects of tannins on the drinkability and aging potential of wine

= 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

and often accentuated by heavy

oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

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 In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

) into delicious and complex elements of "bottle bouquet" when the wine is cellared under appropriate temperature conditions, preferably in the range of a constant . Such wines mellow and improve with age with the tannic "backbone" helping the wine survive for as long as 40 years or more. In many regions (such as in

Bordeaux Bordeaux ( , ; Gascon oc, Bordèu ; eu, Bordele; it, Bordò; es, Burdeos) is a port city on the river Garonne in the Gironde department, Southwestern France. It is the capital of the Nouvelle-Aquitaine region, as well as the prefectur ...

), tannic grapes such as

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 wines) typically have lower tannin levels.

Other flavonoids

Flavan-3-ol Flavan-3-ols (sometimes referred to as flavanols) are a subgroup of flavonoids. They are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2''H''-chromen-3-ol skeleton. Flavan-3-ols are structurally diverse and include a range of comp ...

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 A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

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 Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to the Peronosporaceae family. In commercial agriculture, they are a particular problem for growers of cruc ...

. 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. As an antioxidant, there are some studies into the health benefits of moderate consumption of wines high in catechins.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 144. Oxford University Press 2006 . In red grapes, the main flavonol is on average

, followed by

myricetin Myricetin is a member of the flavonoid class of polyphenolic compounds, with antioxidant properties. Common dietary sources include vegetables (including tomatoes), fruits (including oranges), nuts, berries, tea, and red wine. Myricetin is struc ...

kaempferol Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods including kale, beans, tea, spinach, and broccoli. Kaempferol is a yellow crystalline solid with a meltin ...

, laricitrin,

isorhamnetin Isorhamnetin is an O-methylated flavon-ol from the class of flavonoids. A common food source of this 3'-methoxylated derivative of quercetin and its glucoside conjugates are pungent yellow or red onions, in which it is a minor pigment, quercetin ...

, and syringetin. 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.

Myricetin Myricetin is a member of the flavonoid class of polyphenolic compounds, with antioxidant properties. Common dietary sources include vegetables (including tomatoes), fruits (including oranges), nuts, berries, tea, and red wine. Myricetin is struc ...

, laricitrin and syringetin, flavonols which are present in red grape varieties only, can be found in red wine.

Non-flavonoids

Hydroxycinnamic acids

Hydroxycinnamic acid Hydroxycinnamic acids (hydroxycinnamates) are a class of aromatic acids or phenylpropanoids having a C6–C3 skeleton. These compounds are hydroxy derivatives of cinnamic acid. In the category of phytochemicals that can be found in food, there ...

s are the most important group of nonflavonoid phenols in wine. The four most abundant ones are the

tartaric acid Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally ...

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 acid Ferulic acid is a hydroxycinnamic acid, an organic compound with the formula (CH3O)HOC6H3CH=CHCO2H. The name is derived from the genus ''Ferula'', referring to the giant fennel ('' Ferula communis''). Classified as a phenolic phytochemical, ferul ...

s).

Stilbenoids

''V. vinifera'' also produces

s. 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. 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. 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 Muscadines 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.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 569. Oxford University Press 2006 . Piceatannol is also present in grape from where it can be extracted and found in red wine.

Phenolic acids

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.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 727. Oxford University Press 2006 .

Phenols from oak ageing

Oak barrel will add compounds such as

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 redox, reduction.J. Robinson (ed), ''"The Oxford Companion to Wine"''. Third Edition, p. 492, Oxford University Press 2006, . 4-Ethylphenol and 4-ethylguaiacol are produced during ageing of red wine in oak barrels that are infected by brettanomyces .

Natural phenols and polyphenols from cork stoppers

Low molecular weight polyphenols, as well as ellagitannins, are susceptible to be extracted from Cork (material), cork stoppers into the wine. 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. Guaiacol is one of the molecules responsible for the cork taint wine fault.

Phenolic content in relation with wine making techniques

Extraction levels in relation with grape pressing techniques

Flash release (oenology), Flash release is a technique used in wine pressing (wine), pressing. The technique allows for a better extraction of phenolic compounds.

Microoxygeneation

The exposure of wine to microoxygenation, oxygen in limited quantities affects phenolic content.

Phenolic compounds found in wine

Comp LC pinot vs rose vs white wine 280 nm

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. * Acutissimin A * aesculetin * Anthocyanidin-caftaric acid adducts * Astilbin * Astringin * B type proanthocyanidin dimers * B type proanthocyanidin trimers * Caffeic acid * Caftaric acid * Castalagin * Castavinol C1 * Castavinol C2 * Castavinol C3 * Castavinol C4 * Catechin * Catechin-(4,8)-malvidin-3-O-glucoside * Compound NJ2 * Coniferyl aldehyde * Coumaric acid * Coutaric acid * Cyanidin * Cyanin (anthocyanin), Cyanin (Cyanidin-3,5-O-diglucoside) * Cyanidin 3O-glucoside * Cyanidin acetyl 3O glucoside * Cyanidin coumaroyl 3O glucoside * Cyanidin-3-O-glucoside-pyruvic acid * Cyanidin-3-O-acetylglucoside-pyruvic acid * Cyanidin-coumaroylglucoside-pyruvic acid * Delphinidin * Delphinidin 3O glucoside * Delphinidin acetyl-3O glucoside * Delphinidin coumaroyl 3O glucoside * Delphinidin-3-O-glucoside-pyruvic acid * Delphinidin-3-O-acetylglucoside-pyruvic acid * Delphinidin-3-O-coumaroylglucoside-pyruvic acid * Delphinidin-3-O-glucoside-4-vinylcatechol * Delphinidin-3-O-acetylglucoside-4-vinylcatechol * Delphinidin-3-O-coumaroylglucoside-4-vinylcatechol * Delphinidin-3-O-glucoside-4-vinylphenol * Delphinidin-3-O-acetylglucoside-4-vinylphenol * Delphinidin-3-O-coumaroylglucoside-4-vinylphenol * Delphinidin-3-O-glucoside-4-vinylguaiacol * Delphinidin-3-O-glucoside-4-vinyl(epi)catechin * Delphinidin-3-O-acetylglucoside-4-vinyl(epi)catechin * Delta-viniferin * Dihydro-resveratrol * Ellagic acid * Engeletin * Epicatechin gallate * Epigallocatechin * Epsilon-viniferin * Ethyl caffeate * Ethyl gallate * Ethyl protocatechuate * 4-Ethylguaiacol * 4-Ethylphenol * Fertaric acid * Ferulic acid * Gallic acid * Gentisic acid * Grandinin * Grape reaction product (GRP) * Guaiacol * Hopeaphenol * p-Hydroxybenzoic acid * Isorhamnetol 3-glucoside * Kaempferol * Kaempferol glucoside (astragalin) * Kaempferol glucuronide * Malvidin * Malvidin 3O-glucoside (oenin) * Malvidin acetyl-3O-glucoside * Malvidin cafeoyl-3O-glucoside * Malvidin coumaroyl-3Oglucoside * Malvidin glucoside-ethyl-catechin * Malvidin-3-O-glucoside-pyruvic acid * Malvidin-3-O-acetylglucoside-pyruvic acid * Malvidin-3-O-coumaroylglucoside-pyruvic acid * Malvidin-3-O-glucoside-acetaldehyde * Malvidin-3-O-acetylglucoside-acetaldehyde * Malvidin-3-O-coumaroylglucoside-acetaldehyde * Malvidin-3-O-glucoside-4-vinylcatechol * Malvidin-3-O-acetylglucoside-4-vinylcatechol * Malvidin-3-O-coumaroylglucoside-4-vinylcatechol * Malvidin-3-O-glucoside-4-vinylphenol * Malvidin-3-O-acetylglucoside-4-vinylphenol * Malvidin-3-O-coumaroylglucoside-4-vinylphenol * Malvidin-3-O-caffeoylglucoside-4-vinylphenol * Malvidin-3-O-glucoside-4-vinylguaiacol * Malvidin-3-O-acetylglucoside-4-vinylguaiacol * Malvidin-3-O-coumaroylglucoside-vinylguaiacol * Malvidin-3-O-glucoside-4-vinyl(epi)catechin * Malvidin-3-O-acetylglucoside-4-vinyl(epi)catechin * Malvidin-3-O-coumaroylglucoside-4-vinyl(epi)catechin * Methyl gallate * Myricetol * Myricetol 3-glucoside * Myricetol 3-glucuronide * Oxovitisin A * Pallidol * Pelargonin (Pelargonidin 3,5-O-diglucoside) * Peonidin 3O-glucoside * Peonidin acetyl-3O-glucoside * Peonidin-3-(6-p-caffeoyl)-glucoside * Peonidin coumaroyl 3O-glucoside * Peonidin-3-O-glucoside-pyruvic acid * Peonidin-3-O-acetylglucoside-pyruvic acid * Peonidin-3-O-coumaroylglucoside-pyruvic acid * Peonidin-3-O-glucoside-4-vinylcatechol * Peonidin-3-O-acetylglucoside-4-vinylcatechol * Peonidin-3-O-coumaroylglucoside-4-vinylcatechol * Peonidin-3-O-glucoside-4-vinylphenol * Peonidin-3-O-acetylglucoside-4-vinylphenol * Peonidin-3-O-coumaroylglucoside-4-vinylphenol * Peonidin-3-O-glucoside-4-vinylguaiacol * Peonidin-3-O-glucoside-4-vinyl(epi)catechin * Peonidin-3-O-acetylglucoside-4-vinyl(epi)catechin * Petunidin * Petunidin 3O glucoside * Petunidin acetyl-3O-glucoside * Petunidin coumaroyl-3O glucoside * Petunidin-3-O-glucoside-pyruvic acid * Petunidin-3-O-acetylglucoside-pyruvic acid * Petunidin-3-O-coumaroylglucoside-pyruvic acid * Petunidin-3-O-glucoside-4-vinylcatechol * Petunidin-3-O-acetylglucoside-4-vinylcatechol * Petunidin-3-O-coumaroylglucoside-4-vinylcatechol * Petunidin-3-O-glucoside-4-vinylphenol * Petunidin-3-O-acetylglucoside-4-vinylphenol * Petunidin-3-O-coumaroylglucoside-4-vinylphenol * Petunidin-3-O-glucoside-4-vinylguaiacol * Petunidin-3-O-glucoside-4-vinyl(epi)catechin * Petunidin-3-O-acetylglucoside-4-vinyl(epi)catechin * Phloroglucinol carboxylic acid * Piceatannol * Piceids * Pinotin A * Oligomeric procyanidins : ** Procyanidin B1 ** Procyanidin B2 ** Procyanidin B3 ** Procyanidin B4 ** B1-3-O-gallate ** B2-3-O-gallate ** B2-3'-O-gallate ** procyanidin C1 (epicatechin-(4β→8)-epicatechin-(4β→8)-epicatechin) ** Procyanidin C2 (catechin-(4α→8)-catechin-(4α→8)-catechin) ** procyanidin T2 (trimer) * Protocatechuic acid * protocatechuic aldehyde * Quercetin * Quercetol glucoside * Quercetin 3-O-glucuronide, Quercetol glucuronide * Resveratrol * Roburin A * Roburin E * Scopoletin * Sinapic aldehyde * Sinapinic acid * Syringic acid * Tyrosol * Vanillic acid *

* Vescalagin * 4-Vinylphenol * Vitisin A (pyranoanthocyanin), Vitisin A * Vitisin B (pyranoanthocyanin), Vitisin B * Vinylpyranomalvidin-3O-glucoside-procyanidin dimer * VinylpyranoMv-3-coumaroylglucoside-procyanidin dimer * Vinylpyranomalvidin-3O-glucoside-catechin * Vinylpyranomalvidin-3O-coumaroylglucoside-catechin * Vinylpyranomalvidin-3O-phenol * Vinylpyranopetunidin-3O-glucoside-catechin * Vinylpyranopeonidin-3O-glucoside-catechin * Vinylpyranomalvidin-3O-acetylglucoside-catechin

Effects

Polyphenol compounds may interact with Volatile organic compounds, volatiles and contribute to the aromas in wine. Although wine polyphenols are speculated to provide

or other benefits, there is little evidence that wine polyphenols actually have any effect in humans. 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.

References

External links

Wine polyphenols vary with age and variety (Polyphenols on www.guideduvin.com)
{{in lang, fr
Polyphenol concentrations in red, white and rosé wines at www.phenol-explorer.eu
Natural phenols Polyphenols Wine chemistry