Tannins [3]
Tannins are an excessively generic term for a broad group of phenolic compounds that are secondary metabolites, not directly involved in growth, development, or reproduction of the grape (Johnson, 2016). They are often grouped together because of similar textural contributions to wine, however they are chemically different compounds derived from different sources.

More accurately tannins should be referred to as:

• Hydrolyzable tannins are nonflavonoid-based macromolecules derived from oak.
• Condensed tannins are flavonoid based macromolecules derived from grapes.

Influence on Wine
Zoecklein notes in Red Wine Production Considerations [4] that tannin’s properties include: astringency, bitterness, reaction with ferric chloride, and the traditional identifying factor of protein binding ability. In particular astringency, the characteristic red wine texture that causes drying and puckering in the mouth, is caused by protein binding. In this reaction, both hydrophobic and hydrogen bonding interactions between saliva proteins and wine tannins, causing the proteins to precipitate out of the solution, resulting in a loss of lubrication in the mouth (Johnson, 2016). Additionally tannin size impacts astringency where:

• Smaller polymers have fewer protein binding sites, therefore produce less astringency, provide a greater degree of soft tannins, have more palate depth, and provide a greater reductive strength (Zoecklein, Red Wine Production Considerations).
• Large tannin polymers have a relatively large number of binding sites which interact with proteins, including salivary ones, therefore they may lack softness (be more astringent, “grippy”, possess a dry mouth sensation), and may lack color stability.

​Common Tannin Descriptors
Master of Wine Jacky Blisson's blog post, A Nerdy Little Guide to Tannin Descriptions, provides an extensive list of descriptors and their explanations. It can be found at: jackyblisson.com/wine-tannin-glossary/
​
​Example terms include:

• Light to Medium Tannins: Silky, Rounded, Supple
• Medium to High Tannins: Velvety, Plush
• Very High Tannins: Muscular, Grippy, Chewy
• Negative Descriptors: Astringent, Harsh, Hard

 ​General Reactions of Polyphenols in Wine
In wine, polyphenols often react with each other to form more stable molecules. These reactions are often not instantaneous, however, because they are catalyzed by other compounds.

Reactions that create stable polyphenols are influenced by:
Complexing (binding) with other phenols, yeast byproducts like hydrogen sulfide, mercaptans, and sulfur containing amino acids, and enzymes (Zoecklein, Red Wine Production Considerations).

Aldehyde Bridging occurs between different polyphenols and allows them to covalently bond with each other. This is predominantly acetaldehyde though other aldehydes like furfural, an aldehyde found in new oak, function similarly (Leuck, 2020).

Oxygen exposure. [5] In particular, the formation of acetaldehyde by ethanol oxidation.

Time.

• In young wines they are less stable and more likely to react with other compounds in the wine. They are also less complex and directly derived from the grape or oak (if applicable) as they have a greater percentage of phenols in the monomeric form. For example the wine changes from a purple hue which is influenced by anthocyanins complexing with themselves when young, to a brick red color caused by anthocyanins complexing with tannins and hydroxycinnamates. This also generally corresponds with a reduction in astringency.
• In older wines they are more stable (less reactive), and more complex as they are composed of different types of polyphenols.

Examples of stable color compounds include:

• Polymeric Anthocyanins
  Formed by Anthocyanins + Condensed tannins
• Pyranoanthocyanins
  Formed by Anthocyanin + Hydroxycinnamates

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​Flavonoids

​Flavonoids are found in the skins, seeds, and stems of grapes. In red wines, they typically constitute more than 85% of the phenolic content, and in white wines, they typically constitute less than 20% of the total phenolic content (Jackson, Wine Science). Their concentration typically increases as the berries are exposed to sunlight. Types include:

• Flavonols
• Flavan-3-ols (flavanols)

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Flavonols [6]
What They Are:
Yellow pigments that directly contribute white wine color, though they are masked by anthocyanins in red wines7 (Castillo-Munoz, 2007).

Concentration Is Impacted by:

• Grape UV light exposure. Flavonols function as a grape’s “sunscreen” and are influenced by viticultural practices.
• Elevated growing temperatures may inhibit flavonol biosynthesis.
• Cultivars vary in total flavonols produced, as well as different proportions of the different flavonol compounds.

Influence on Wine:

• In white wine, flavonols directly act as yellow pigments.
• In red wine copigmentation can cause a tenfold increase in color absorbance and a 5-20 nm bathochromic shift in color, which makes the wine appear more purple. Copigmentation occurs when flavonols complex with flavylium ions (the colored form of anthocyanins), thereby promoting the formation of more flavylium ions. As the wine ages, the copigmentation complexes are broken and polymerized pigments (anthocyanin-tannin complexes) form.

Types Include8:
The main flavonols include myricetin, quercetin, kaempferol, and isorhamnetin. They are often bound to a sugar molecule like glucose and hydrolyzed (broken down) during winemaking and aging. [9]

In red grapes:

• The main flavonol is quercetin, followed by myricetin, kaempferol, laricitrin, isorhamnetin, and syringetin.
• Quercetin is not very soluble in wine, and as wine ages, it can form a haze or crystalline sediment, an issue sometimes observed in Sangiovese wines.

In white grapes:

• The main flavonol is quercetin, followed by kaempferol, and then isorhamnetin.
• The other three are absent from white grapes.

Flavan-3-ols (flavanols)
What They Are:
Small polyphenols also known as flavanols (not flavonols).

Concentration is impacted by:
Synthesized primarily in seeds and stems (Jackson, Wine Science) with some synthesis in skins. For this reason, in cool growing regions or cool vintage years, seeds and stems can be used in winemaking to increase the flavan-3-ol content if skin tannins are low.

Influence on Wine:
See the section: “Proanthocyanidins”

Types Include:
Angelosante (2020) in GuildSomm notes several analogues may impart different sensory characteristics, and can consist of:
​​
Catechins and Epicatechin
(Isomers of each other)

• Primarily found in: Grape seeds
• Concentration is influenced by:
  • Seed maturity as catechins become less extractable as the seed (and grape) mature. This occurs through an oxidation of the tannins and the development of a waxy coating on seed. In the vineyard, this maturity can be tested by tasting the seed for nuttiness (which is less bitter).
• Influence on wine
  • Described as rough, coarse, unripe (Angleosante, 2020)
  • The Catechin to Tannin Ratio is an indicator of seed maturity. As during grape ripening, catechin becomes less extractable and skin tannins become more extractable therefore the ratio of catechin to tannin decreases. This lower ratio means lower tannic qualities. For example Pinot Noir is lighter and has a lower Catechin: tannin ratio than Syrah. [10]

Gallocatechins and Epigallocatechin

• Primarily found in: Grape skins
• Influence on Wine: Described as velvety, viscous, ripe (Angelosante, 2020)

Color enhancement of Red Wine
Mega Purple or Mega Red from Vie-Del Co. are concentrates derived from high anthocyanin content grapes including French-American hybrids which contain maldovin diglucoside version of anthocyanins. Used similarly to caramel color in whiskey and rum, a little provides color uniformity without impacting flavor, while using a lot will impact both. For example, these concentrates can cover up pyrazines and mask elements of brettanomyces. Its usage in wine is debated and can be secretive. A discussion on usage can be found at: winesvinesanalytics.com/features/article/51033/Mega-Purple

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Anthocyanins and Anthocyadins [9]

• What they Are
• Concentration Is Impacted
• Influence on Wine
• Types Include

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Anthocyanins and Anthocyadins [9]

What They Are:

• A class of flavonoids with different molecular structures.
• Anthocyanins are composed of anthocyanidins that have a glucose molecule attached.
• Anthocyanidins refer to a simple flavonoid ring system, the core of which is flavylium.
• Acylated anthocyanins have an acetic acid attached to the sugar molecule. These are more color-stable and soluble than the non-acylated analogue, and they can confer deeper color intensity to the wine (Angelosante, 2020).
  
  

Concentration Is Impacted by [11]

Grape varietal

• For example, Pinot Noir does not synthesize para-coumaroylated or acetylated anthocyanins, whereas other varieties do.
• Acylated anthocyanin concentration in a wine is influenced by grape variety and growing conditions. For example, light-colored grape varieties, including Gamay, Sangiovese, Nebbiolo, and Grenache, contain only a small proportion (Angelosante, 2020).
• In some cultivars like Tempranillo and Cabernet Sauvignon, “high-quality” grapes had higher anthocyanin content than “low-quality” grapes. However, in cultivars like Grenache, the opposite is true. [11]

Growing conditions

• Water stress during ripening influences biosynthesis of flavonoids like anthocyanin through an increase in production of the phytohormone abscisic acid, and berry dehydration, which concentrates the anthocyanins.
• Growing climate temperature. Typically the lowest concentration of anthocyanins in the berries is obtained in the warmest year, whereas higher concentrations are produced in cooler years:12
• Low temperatures of ~25 °C favor anthocyanin biosynthesis.
• High temperatures of ~35 °C are associated with anthocyanin degradation and inhibition of anthocyanin accumulation.
• Treatments of harvested grapes. Low storage temperatures increase the accumulation of anthocyanins, whereas simultaneous high CO2 treatment lessens the gene expression and anthocyanin accumulation.

Viticultural practices

• Cluster thinning subsequent to fruit setting may help to regulate yield and advance fruit maturity, increase bunch and berry weights, enhance the anthocyanin accumulation, and improve fruit quality.13 The study by Petrie and Clingeleffer (2008) did not include leaf area to fruit ratio, however. Cluster thinning at veraison minimally impacts ripening time and the weight of grape skins, and it can result in a lower total acidity, slightly higher pH, and a higher concentration in berry skin. [14]
• Conventionally-grown grapes may produce higher levels of anthocyanins than organic or biodynamic vineyards.
• Soil acidity can influence anthocyanin accumulation, depending on the cultivar. Yokotsuka et al (1989) found that in alkaline soil there was a higher accumulation of total phenols, total red pigments, and total anthocyanins. [15]

Influence on Wine:
Anthocyanins and anthocyanidins influence wine color. Beyond concentration, color is also influenced by secondary reactions, which include:

Direct pigmentation, where anthocyanins vary by hue with some being more red and others more purple. The color of wine is influenced by:

• The proportion of each type of anthocyanin.
• The total amount of anthocyanins.
• The grape cultivar and growing conditions which dictate the anthocyanin accumulation.

Complexing with other phenols during vinification, and aging into polymeric structures to form stable pigments, as the “free” anthocyanins in “young wine” are relatively unstable (Angelosante, 2020), (Zoecklein, 2001). This includes both short-term mechanisms and relatively long-term reactions to form polymeric pigments, including:

• Anthocyanin self-association or with other flavonoids in short term reactions (Formaker, 2015).
• Complex with tannins of grapes and oak in long-term reactions to form pigmented tannins like pyranoanthocyanins (Formaker, 2015). For more see section on “Pyranoanthocyanins”.
• Traditionally, the cofermentation of red and white grapes has been used to enhance color stability, possibly the result of enhanced copigmentation. Classic examples of this include Syrah and Viognier, Sangiovese with Trebbiano and Malvasia (Angelosante, 2020).

Wine pH. Formaker (2015) notes that anthocyanins and anthocyanidins express color differently based upon pH. This, in turn, along with anthocyanin and anthocyanidin concentration, impacts the color of the wine:

Anthocyanins
The form factors which depend on pH and influence color are:

• As a flavylium ion at pH >2, they are intensely red or orange.
• As a quinoidal-base in alkaline conditions, they appear blue.
• If in the chalcone or carbinol pseudobase at neutral pH they are colorless.

Anthocyanidins

• Are colored in low pH (acidic) conditions.
• Are colorless in higher pH (alkaline) conditions.

Sulfur dioxide (SO2) slows or inhibits the formation of the tannin-anthocyanin complex by binding to acetaldehyde, which ties up the bridge needed in the formation of the complex.

Controlled aeration post-fermentation increases the rate of reaction of coloring matter with tannins, resulting in condensation, polymerization and enhanced suppleness (Zoecklein, 2001).

Types Include

Malvidin
The most populous in red grape varieties represents ~40% of the anthocyanins, and makes up the majority of the red pigments that are acylated (He et al., 2010).

• Color: More blue (an example is Anagallis monelli, or blue pimpernel) at alkaline pH, and the reddest individual anthocyanidin at the wine pH (He et al. 2010).

Cyanidin

• Color: Red at pH <3, violet at pH 7-8, and blue at pH >11.

Delphinidin

• Color: Purplish like Delphinium. [16]

Peonidin

• O-methylated anthocyanidin derived from cyanidin.
• Color17: Purplish-red hues like the peony, from which it takes its name.

Petunidin

• Derived from Delphinidin, it is an o-methylated anthocyanidin of the 3-hydroxy type.
• Color: Dark-red or purple E163 of the www.safefood.net/food-colour-index.
• Pelargonidin is a rare anthocyanin in grapes.

For more more technical insight
He, F., Liang, N. N., Mu, L., Pan, Q. H., Wang, J., Reeves, M. J., & Duan, C. Q. 2012. Anthocyanins and their variation in red wines I. Monomeric anthocyanins and their color expression. Molecules, 17(2), 1571-1601. www.mdpi.com/1420-3049/17/2/1571

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Proanthocyanidins: Condensed Tannins/ Non-Hydrolysable Tannins [18]

• What They Are
• Concentration is impacted by
• Influence on Wine

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What They Are:

• 2 to 80+ flavan-3-ol units that are held together by covalent bonds (Johnson, 2016). This helps stabilize them under acidic conditions.
• A condensed tannin’s length can be measured in mean degrees of polymerization (mDP).
• The term “tannin” often refers to condensed tannins. Their unpleasant flavor functions as a deterrent to animals and insects that try to eat foliage or unripe fruit (Angelosante, 2020 GuildSomm).

Concentration is impacted by
Synthesized primarily in seeds, stems and flesh. They account for about 25-50% of the phenols in wine and constitute approximately 0.3 to 2.0 grams per liter in red wine.

Grape type
Pinot noir for example does not appear to produce skin tannins and have a low proportion of seed tannins, which might explain their poor color intensity, and why stems may need to be added to the ferment (Jackson, Wine Science).

The growing climate at both macro (region) and micro (vineyard) level impacts composition and accumulation of condensed tannins during berry development.
For more on this: www.hawaiibevguide.com/viticulture

Production technique
Winemaking practices that increase phenolic extraction increase condensed tannin concentration. Alternatively, if skin contact is minimized like in white wine, they contain very little tannins. Similar to this concept, orange wines made from the maceration of white grapes on their skins contain elevated levels of tannins. For more on skin extraction read:
www.hawaiibevguide.com/wine-making-pre-permentation-process

Tissue type
Johnson, 2016 noted:

• Skin tannins are composed of polymeric chains ranging from 3 to 83 subunits of epigallocatechin-derived subunits, as well as trace amounts of gallocatechin and epigallocatechin 3-O-gallate lengths linked by interflavan bonds. For more on seed tannins see “Flavan-3-ols” section.
• Seed tannins consist of catechin and epicatechin polymers of 2 to 16 subunits. For more on seed tannins see “Flavan-3-ols” section.
• Grape pulp tannins are non-extractable, due to a strong association with pulp cell wall constituents.
  
  

Oxygenation during aging oxidizes ethanol to form acetaldehyde.

Aging

• During wine aging, procyanidins slowly combine with monomeric flavonoids to generate tannin polymers of 8-14 units in length.
• Condensed tannin chains can grow to the point where they precipitate out of solution. This can be seen as sediment at the bottom of the bottle.

Influence on Wine:

• Influences perceived as astringency by binding to salivary and other proteins.
• Capable of acting as an antiatherosclerotic, immunologic, antimicrobial, and antiviral agent, as well as a potent antioxidant.
• Stabilizes wine color by an acetaldehyde “bridge” that forms covalent bonds between condensed tannins and anthocyanins.
• See the above section: “Influence on Wine” of “Flavan-3-ols” for the differences in texture between seed tannins and skin tannins.

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Pigmented Tannins /Polymeric Pigments or Anthocyanins:
Anthocyanin + Condensed Tannins

• What They Are
• Concentration is Impacted By
• Influence on Wine
• Types Include

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What They Are:
Formed by the complexing of anthocyanins with flavan-3-ols like catechins, or epicatechin, with proanthocyanidins, or with ellagitannins.20 This process begins at maturation and continues throughout the aging process.

Concentration is Impacted By:

• Temperature, oxygen, and yeast metabolites, and cofactors like metal ions.
• Time, as the concentration of tannin decreases as some settles out of the wine. Excessively tannic wine will not be corrected by extended aging, however.
• Zoecklein, 2001 notes that the rate and extent of oxidation is impacted by adjusting the quantity and timing of dissolved oxygen, sulfur dioxide, and pH. In particular, aeration immediately following fermentation is the most effective time to influence the complexing of tannins with anthocyanins to form stabilized pigments.

Influence on Wine

​Color [21]

• Color changes from purple to red-brown during wine aging, but colors can range from orange to blue (in alkaline solutions).
• Reactions under oxidative conditions also lead to brown-orange pigments that do not derive from anthocyanins.

Impacts mouthfeel, especially astringency, as it is dependent on the size of the polymer chain.

• Smaller polymers (shorter chains) lead to smaller colloids, which have a softer mouthfeel (Johnson, 2016).
• Angelosante (2020) notes that short chains form when there is a higher concentration of anthocyanins to tannins, because as anthocyanin binds to tannin, it essentially forms a cap on one end of the chain that prevents further polymerization. This also reduces the concentration of purple pigments.

Ageability is influenced by the amount of tannin and anthocyanin—and perhaps more importantly, the amount of anthocyanin-rich polymeric pigment (Angelosante, 2020).

Polymeric Anthocyanin to Tannin Index is the ratio of stabilized color compared to overall tannins in the wine. Leuck (2020) notes:

• Low index wine is light in color high in tannin structure. Nebbiolo, Barolo, Barbaresco for example.
• A high index wine is dark in color and high in tannin structure. Barossa Shiraz for example.

Types Include: [21]
Given the diversity of the category, there is a difference between:

• Small polymeric pigment: Color is primarily contributed by the berry.
• Large polymeric pigments are formed during fermentation.

For additional insight read:
Cheynier, V., Duenas-Paton, M., Salas, E., Maury, C., Souquet, J. M., Sarni-Manchado, P., & Fulcrand, H. (2006). Structure and properties of wine pigments and tannins. American Journal of Enology and Viticulture, 57(3), 298-305. www.ajevonline.org/content/57/3/298

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Pyranoanthocyanins:

​Formed when anthocyanins complex with hydroxycinnamates or the yeast-created fermentation byproducts of acetaldehyde, pyruvate and vinylflavanols.

• Concentration Is Impacted by
• Influence on Wine
• Influence on Wine
• Types Include

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Concentration Is Impacted by:
Presence of anthocyanin.

Presence of a partner for the anthocyanins.
In general, pyranoanthocyanin formation occurs when respective precursors appear, either during fermentation, or later during aging, and coincides with the disappearance of anthocyanins, which is most significant over the first couple years of wine aging. Additionally the winemaking processes that increase the concentration of pyranoanthocyanin precursors include:

• Yeast strains that produce more acetaldehyde and pyruvate increase vitisins, which are created when anthocyanin malvidin binds to pyruvate to make vitisin A (malvidin-3-O-glucoside-pyruvate acid) or acetaldehyde to make vitisin B (malvidin-3-O-glucoside-4 vinyl). [23]
• Delayed malolactic fermentation increases vitisins, as the microbes deplete acetaldehyde and pyruvate concentration.[24]
• Maceration techniques that increase the concentration of flavanols and anthocyanins.

Malolactic fermentation. This removes acetaldehyde and pyruvate, so delaying this process is a way to encourage these stable color compounds to form (Angelosante, 2020).

Bottle aging duration:

• Polymers which exceed the solubility of the wine and drop out of solution as sediment in the bottle may also form.
• During aging, free anthocyanins diminish, and copigmentation complexes break down and after a year or two, they contributes little to a wine’s color. This results in redder and less intensely colored wine, (Angelosante, 2020).
• During wine aging, procyanidins slowly combine with monomeric flavonoids to generate polymers (tannins) between 8 to 14 units in length, with a molecular weight of 2000-5000 daltons (Jackson, Wine Science).

Unlike anthocyanins, pyranoanthocyanin color is not bleached by bisulfite or by high wine pH.


Types Include [25]:
Vitisins
They are a class of pyranoanthocyanins formed through binding with fermentation byproducts.
Concentration is generally impacted by26:

• The concentration of anthocyanins extracted from the skins of grape berries prior to or during fermentation.
• Pyruvic acid and acetaldehyde's availability for anthocyanins to complex with is influenced by:
• Microbial metabolism.
• Malolactic fermentation. This process entails the consumption of pyruvic acid and acetaldehyde by lactic acid bacteria, so delaying or forgoing the process can increase vitisin synthesis.
• Oxidative processes like barrel aging and micro-oxygenation.

Influence on Wine:
Contributes stable wine color relative to anthocyanins (Rentzsch et al. 2007a).

• Most compounds exhibit a red-orange color that is believed to contribute to the brick-red hue observed in aged wine; however, one class (portisins) is blue in color.
• Pyranoanthocyanins are not subject to bleaching, and range in color from red-orange to yellow to blue (Angelosante, 2020).

Influence on Wine:

• Contributes 11-14 times more color than unmodified anthocyanins, and exhibits a hypsochromic shift towards an orange-red hue.
• Due to the pyran ring structure, its stable against discoloration by changes in pH or bleaching by sulfur dioxide.

Vitisin Types Include:

Vitisin A Carboxypyranoanthocyanins (Malvidin-3-O-glucoside-pyruvate acid)

• Formed by:
  • The reaction between pyruvic acid and the anthocyanins. This is especially high during the first days of alcoholic fermentation, when about 50% of must sugar has been fermented due to the elevated concentration of pyruvate, then it drops when the yeast starts to reuse part of the excreted pyruvate.
  • Vitisin A concentration is higher than Vitisin B, due to the malvidin-3-O-glucoside prevalent anthocyanin.
  • Temperature impacts formation, as the maximum production of vitisin A is reached at 10-15 °C, whereas higher temperatures (32 °C) favor the formation of polymeric pigments.
• Impact on Wine:
  • Due to its low rate of degradation and potential to be formed during aging, more than half of the initial content of Vitisin A remains in wines after 15 years.

Vitisin B: Malvidin-3-O-glucoside-4 vinyl
Differs from carboxypyranoanthocyanins lacking the carboxyl group in the C10 position of ring D.
Formed by:

• The reaction between acetaldehyde and anthocyanin, preferentially of the acetylated anthocyanins type, and less preferentially, coumaroylated anthocyanins.
• The synthesis of type B vitisins begins towards the end of alcohol fermentation, as acetaldehyde production is proportional to the amount of the fermented sugar.

Methylpyranoanthocyanins
Formed by the reaction between anthocyanins and yeast metabolites like acetone.
In wine, these derivatives show a yellow-orangish color (maximum wavelength of 478 nm) at wine pH.
​
Pinotins

• Formed by: Complexing of malvidin 3-glucoside (an anthocyanin) and hydroxycinnamic acids (including p-coumaric, caffeic, ferulic, sinapic acid or their decarboxylation product of 4-vinylphenols) via covalent bonding.27
• Impact on Wine:
  • At the wine pH, these pigments are reddish-orange (505–508 nm).
  • Because concentration of Pinotin A can be 10 times higher in wines aged for 5 or 6 years than in young wines (possibly because these compounds are formed whenever there are free anthocyanins and hydroxycinnamic acids), they can be used as markers for the aging time in wines.

Flavanyl-Pyranoanthocyanins

• Formed by: A pyranoanthocyanin molecule directly joined to a favanol.
• Wine Impact: These pigments create a hypsochromic shift (of 490–511 nm) towards a more orangish color than the starting anthocyanins.

Non-flavonoid phenols are found in the grape berry and are commonly esterified to sugars, organic acids or alcohols. Types include:

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Non-flavonoids

Phenolic Acids: Hydroxycinnamates/ Hydroxycinnamic acids [29]

• What they Are
• Concentration is impacted by
• Influence on Wine
• Types Include

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What They Are:

• A group containing only one aromatic ring and one carboxylic acid group, with its simplest form being cinnamic acid.
• In grapes, they are found in the skins and pulp, and can be esterified with ethanol. They are mostly found as esters of tartrates.
• These are the most abundant non-flavonoids in wine (Angelosante, 2020 GuildSomm).

​Concentration is impacted by:
Produced by phenylalanine precursors through the shikimate metabolic pathway by non-animal organisms during fermentation from the hydrolysis of hydroxycinnamic tartaric esters. [30]

Influence on Wine:

• If tartrates are hydrolyzed during fermentation, it frees cinnamates, which in turn can be decarboxylated by yeasts, including Brettanomyces, into volatile phenols, including 4-vinylphenol from coumaric acid, 4-ethylphenol (4-EP), from caffeic acid, and 4-ethylguaiacol (4-EG), from ferulic acid (Angelosante, 2020), (Angulo, 2016).  These give wine a barnyard smell, which can be unwanted.
• Can be an oxidation substrate (a white wine browning precursor), and give bitter flavor (Merkyte et al 2020).
• Can act as cofactors in copigmentation, and are the most important phenolic compounds in white wines (Angelosante, 2020 Guild-Somm).

Types Include:

• Cinnamic acids: coumaric acid and its ester form Coutaric acid, ferulic acid and its ester form fertaric acid, chlorogenic acid (Jackson, Wine Science), (Angelosante, 2020).
• Caffeic acid is prone to enzymatic oxidation by phenol oxidases and oxygen (Angulo, 2016), and acts as a copigment in red wine. [31]

Stilbenoids [32]

• What they Are
• Concentration is impacted by
• Influence on Wine
• Types Include

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A class of compounds which are synthesized by grapes and other plants as phytoalexins, a substance produced by
plant tissues in response to biotic and abiotic stresses.

​Vine stress.

Research suggests that stilbenoids’ im- portance in the winemaking process is limited to their role as a phytoalexin in grapevines. That is, they influence vine health in the sense that they are a response to microbial or abiotic stress, namely fungal infection and exposure to UV radiation. Otherwise, their activ- ity in wine is relatively static, and does not significantly contribute to the re- duction of oxidative compounds.

Resveratrol, which was popularized by a 1992 study which reported that resveratrol seemed to inhibit tumor growth in certain animal models. However, subsequent research has shown that the quantities for this to occur is the equivalent of 266 bottles of wine.

​For a more in-depth look at stilben- oids in grapes: Pawlus, A. D., Waffo-Téguo, P., Shaver, J., & Mérillon, J.-M. (2012). Stilbenoid chemistry from wine and the ge- nus Vitis, a review. OENO One, 46(2), 57–111. https://doi.org/10.20870/oeno- one.2012.46.2.1512

Hydrolysable Tannins (Oak Tannins) [33]

• What They Are
• Concentration is impacted by
• Influence on Wine
• Types Include

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What They Are:

Hydrolyzable tannins are polymers of hydroxybenzoic acid.

Hydroxybenzoic acid is composed of a complex mixture of oligomers of gallic acid or egallic
acid which are bonded by oxidative-coupled and ester linkages to glucose.

The two types are based upon the hydroxybenzoic acid composition where:

• Gallotannin is composed of gallic acid
• Egallatannin is composed of egallic acid.

These tannins are chemically different from condensed tannins. In wine’s acidic conditions, the low pH weakens the bonding between hydrogen and oxygen atoms of the associated moieties, causing the ellagitannin to hydrolyze into gallic acid and its dilactone, ellagic acid (Jackson, Wine Science).

Concentration is impacted by:

• The quantity extracted from oak. This quantity is influenced by the type of oak, duration of contact, the surface area of the vessel it was aged in, the oak barrel production process, and other winemaking techniques. For more on oak extraction, read: www.hawaiibevguide.com/a-guide-to-oak-barrel-aging.
• Barrel toast in particular is influential, as untoasted oak is rich in hydrolyzable tannins, whereas toasting converts hydrolyzable tannins to products that can form larger polymers that do not help increase color.
• Malolactic fermentation is believed to increase the release and solubility of oak aroma compounds.
• Barrel Type: Wines aged in chestnut cooperage extract slightly different, but related, hydrolyzable tannins and non-flavonoids (Jackson, Wine Science).
• Grape stems can also contribute hydroxybenzoic acids. [34]

Influence on Wine

Zoecklein, in Barrels, Barrel Adjuncts, And Alternatives Part 3, notes the following influences of oak tannins on wine:

• They have been recently revealed in studies to potentially increase the perception of astringency, bitterness, and roundness in wine (Angelosante, 2020).
• Untoasted oak may help to limit the negative influences of some sulfur-like off odor compounds, facilitating the perception of fruit.
• Green untoasted oak contains trans-2-nonenal, which provides sawdust and planky-type aromas that can persist in wines for a long time. For this reason, oak requires curing or seasoning (12 to 24 months) to help leach harsh tannins.
• Moderate to heavy toasting can provide clove, spice, vanilla, caramelized, and espresso aroma that can frame the fruit and also add a richness to the palate, as a result of the enhanced wood sugars. It can also impart barbecue aromas, which can be amplified by yeast and converted to Worcestershire aromas.

Copigmentation between gallic acid or ellagic acid and anthocyanins increases the spectral color of red wines (Jackson, Wine Science).

Enhances ageability of low-phenol reds like Pinot Noir because of gallic acid’s antioxidant properties (reductive strength).

Help to precipitate out wine proteins and deactivate enzymes which may destroy color during fermentation.

Can minimize the impact of botrytis produced lacasse through its antioxidant properties (Leuck, n2020). For example:

• European oak aging is used because it is high in ellagic tannins.
• Gallic acid can be isolated from oak and made into a commercially available product like Laffort Tannin Galalcool (laffort.com/en/products/tanin-galalcool).

Types Include

Castalagin and vescalagin, which are the most frequently extracted ellagitannins (Jackson, Wine Science).

Laboratory Phenolic Analysis
A lab like ETS Labs can conduct a phenolic panel for wineries. The panel measures: Catechin, Catechin/tannin ratio, Polymeric Anthocyanins, Polymeric Anthocyanins/Tannin Ratio, Tannins, Total
Anthocyanins

For more insight: www.etslabs.com/analyses/%23JGEXTB

​Enological Tannins/ Alternative Oak Products

• What They Are
• Process
• Types Include

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Enological tannins can be used to provide oak aromas and additional tannins without the influence of microoxygenation from barrel aging. Oak can also bind to and remove polar compounds like organosulfur compounds and pyrazines, thereby reducing herbaceous notes in the wine. [35]

According to Zoecklein (2005), the timing of tannin addition in wine-
making is important under certain usage cases, where:

• Earlier addition has less negative impacts than later addition, as it allows for integration with the other structural elements, and can allow some tannins to precipitate out of the solution. The degree of precipitation is dependent upon a multitude of factors, including the grape variety and the season, and is why some winemakers use multiple additions during fermentation.
• If used early, oak alternatives can help to manage red wine color and tannins, but provide only limited aromatics.
• Oak alternatives used during white wine fermentation may not be optimal for some varieties, such as Sauvignon Blanc, with rather oxygen-labile aroma compounds.

Types Include [36]
*Dosage rates are references from www.stavin.com/dosage-rates

Oak extract

• Made by soaking oak chunks or chips in high-proof alcohol.
• Addition: Added to the finished wine at a rate of 1-2L per ton of grapes to improve midpalate structure, add nostalgic aromas, and develop an extended finish. [37]

Oak powder

• During fermentation, powder is added in loose form after destemming the grapes. Full extraction occurs by the finish of fermentation and the powder is removed when the must is pressed. Add at a rate of 0.5-2 lbs per ton.
• Post-fermentation, a portion of the wine may be infused with oak powder. Then, after the oak has been extracted, it is blended with the unoaked wine, thereby providing greater control.

Oak chips

• During fermentation, chips are added loose after the grapes have been destemmed. Fairly complete extraction occurs during fermentation. Add at a rate of 2-8 lbs per ton.
• Post-fermentation chips are added in a food grade bag made of nylon or another inert material. This bag containing the oak chips is steeped in the wine, with a minimum contact time of one week.

Oak cubes/beans/stave segments

• During fermentation, beans are added in bags and held under the cap, and can be kept in the wine in the press tank for malolactic fermentation and aging. Addition is at 4-8 lbs per ton.
• Post fermentation, a food grade bag made of nylon or another inert material containing the oak chips is steeped in the wine. Minimum contact time of two months.

Staves and sticks
Post-fermentation, staves are suspended in the wine. The mechanism of suspension varies depending on the container. Minimum contact time of three months.

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Resources and Suggested Reading

1. Jackson, R. S. (2008). Wine science: principles and applications. Academic press.

2. Angelosante, J. (2020, March 27). A Guide to Wine Phenolics. GuildSomm. Retrieved
June 23, 2022, from www.guildsomm.com/public_content/features/articles/b/jennifer-angelosante/posts/phenolics

3. Johnson, C. (2016). Tannin: Key factors in red wine taste and mouthfeel. Waterhouse
Lab. Retrieved June 23, 2022, from https://waterhouse.ucdavis.edu/whats-in-wine/tannin

4. Zoecklein, B. (2001, November 9). Enology Notes #33. Enology-Grape Chemistry at Virginia Tech. Retrieved June 23, 2022, from www.apps.fst.vt.edu/extension/enology/EN/33.html

5. Zoecklein, B. W. (n.d.). Red Wine Production Considerations: Section 1. Enology-Grape
Chemistry at Virginia Tech. Retrieved June 23, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Red%20Wine%20Production/Red%20Wine%20
Production%20-%20Section%201.pdf

6. Garrison, M. (2015). Flavanols are "sunscreen" for grapes. They have an effect on co-pigmentation. Waterhouse Lab. Retrieved June 23, 2022, from https://waterhouse.ucdavis.edu/whats-in-wine/flavonols

7. Castillo-Muñoz N, Gómez-Alonso S, García-Romero E, Hermosín-Gutiérrez I. Flavonol profiles of Vitis vinifera red grapes and their single-cultivar wines. J Agric Food Chem. 2007 Feb 7;55(3):992-1002. doi: 10.1021/jf062800k. PMID: 17263504.
Retrieved from: www.academia.edu/3552836/Flavonol_Profiles_of_Vitis_vinifera_Red_Grapes_and_Their_Single_Cultivar_Wines

8. Mattivi, F., Guzzon, R., Vrhovsek, U., Stefanini, M., & Velasco, R. (2006). Metabolite profiling of grape: flavonols and anthocyanins. Journal of agricultural and food chemistry, 54(20), 7692-7702. Retrieved from: https://www.academia.edu/15392966/Metabolite_Profiling_of_Grape_Flavonols_and_Anthocyanins

9. Castillo-Muñoz, N., Gómez-Alonso, S., García- Romero, E., & Hermosín-Gutiérrez, I. (2007). Flavonol profiles of Vitis vinifera red grapes and their single-cultivar wines. Journal of agricultural and food chemistry, 55(3), 992-1002.
https://www.academia.edu/3552836/Flavonol_Profiles_of_Vitis_vinifera_Red_Grapes_and_Their_Single_Cultivar_Wines?from=cov

11. He, F., Mu, L., Yan, G. L., Liang, N. N., Pan, Q. H., Wang, J., & Duan, C. Q. 2010. Biosynthesis of anthocyanins and their regulation in colored grapes. Molecules, 15(12), 9057-9091. 
www.mdpi.com/1420-3049/15/12/9057/htm

12. Arozarena, I., Ayestarán, B., Cantalejo, M., Navarro, M., Vera, M., Abril, I., & Casp, A. (2002). Anthocyanin composition of Tempranillo, Garnacha and Cabernet Sauvignon grapes from high-and low-quality vineyards over two years. European Food Research and Technology, 214(4), 303-309. Retrieved from: https://www.researchgate.net/publication/225778385_Anthocyanin_composition_of_Tempranillo_Garnacha_and_Cabernet_Sauvignon_grapes_from_high-_And_low-quality_vineyards_over_two_years

13. Tarara, J. M., Lee, J., Spayd, S. E., & Scagel, C. F. (2008). Berry temperature and solar radiation alter acylation, proportion, and concentration of anthocyanin in Merlot grapes. American journal of enology and viticulture, 59(3), 235-247. Retrieved from:  https://pubag.nal.usda.gov/download/22298/pdf 

14. Petrie, P.R. and Clingeleffer, P.R. (2006), Crop thinning (hand versus mechanical), grape maturity and anthocyanin concentration: outcomes from irrigated Cabernet Sauvignon (Vitis vinifera L.) in a warm climate. Australian Journal of Grape and Wine Research, 12: 21-29. https://doi.org/10.1111/j.1755-0238.2006.tb00040. Retrieved from: https://wineserver.ucdavis.edu/sites/g/files/dgvnsk2676/files/research-summaries/10mechanical%20thin%20.pdf

15. Neira, Alvaro & Cáceres-Mella, Alejandro & Pastenes, Claudio. (2007). Low Molecular Weight Phenolic and Anthocyanin Composition of Grape Skins from cv. Syrah (Vitis vinifera L.) in the Maipo Valley (Chile): Effect of Clusters Thinning and Vineyard Yield. Food Sci. Tech. Int. 13. 10.1177/1082013207077920. https://www.researchgate.net/publication/40882871_Low_Molecular_Weight_Phenolic_and_Anthocyanin_Composition_of_Grape_Skins_from_cv_Syrah_Vitis_vinifera_L_in_the_Maipo_Valley_Chile_Effect_of_Clusters_Thinning_and_Vineyard_Yield 

16. Yokotsuka, K., Nagao, A., Nakazawa, K., & Sato, M. (1999). Changes in anthocyanins in berry skins of Merlot and Cabernet Sauvignon grapes grown in two soils modified with limestone or oyster shell versus a native soil over two years. American journal of enology and viticulture, 50(1), 1-12. https://www.ajevonline.org/content/50/1/1.short

17. Wikipedia contributors. (2022, May 1). Delphinidin. In Wikipedia, The Free Encyclopedia. Retrieved 11:18, June 23, 2022, from https://en.wikipedia.org/w/index.php?title=Delphinidin&oldid=1085662299

18. Wikipedia contributors. (2022, January 7). Peonidin. In Wikipedia, The Free Encyclopedia. Retrieved 11:20, June 23, 2022, from https://en.wikipedia.org/w/index.php?title=Peonidin&oldid=1064223782

19. Harvey, C. (2015). Proanthocyanidins: Polymers of flavan-3-ols; the larger structures are condensed tannins. Waterhouse Lab. Retrieved June 23, 2022, from https://waterhouse.ucdavis.edu/whats-in-wine/proanthocyanidins

20. Adams, D. O. (2017, October 18). Chemical Characterization of Small Polymeric Pigments in Wines and Red Grape – American Vineyard Foundation. American Vineyard Foundation. Retrieved June 23, 2022, from www.avf.org/research-summary/chemical-characterization-of-small-polymeric-pigments-in-wines-and-red-grape/

21. Robinson, J., & Harding, J. (Eds.). The Oxford Companion to Wine. (2015). United Kingdom: Oxford University Press.

22. Harbertson, J. F., Picciotto, E. A., & Adams, D. O. (2003). Measurement of polymeric pigments in grape berry extract sand wines using a protein precipitation assay combined with bisulfite bleaching. American Journal of Enology and Viticulture, 54(4), 301-306. 
 www.ajevonline.org/content/54/4/301.short

23. Angelosante, J. (2015). Pyranoanthocyanins: Derived wine pigments created from grape anthocyanins and reactions with fermentation and oxidation products. Waterhouse Lab. Retrieved June 23, 2022, from waterhouse.ucdavis.edu/whats-in-wine/pyranoanthocyanins 

24. Morata, A., Gómez-Cordovés, M. C., Colomo, B., & Suárez, J. A. (2003). Pyruvic acid and acetaldehyde production by different strains of Saccharomyces cerevisiae: relationship with vitisin A and B formation in red wines. Journal of Agricultural and Food Chemistry, 51(25), 7402-7409.  pubs.acs.org/doi/abs/10.1021/jf0304167

25. Burns, T. R., & Osborne, J. P. (2015). Loss of Pinot noir wine color and polymeric pigment after malolactic fermentation and potential causes. American Journal of Enology and Viticulture, 66(2), 130-137.  https://www.ajevonline.org/content/66/2/130.short

26. Marquez, A., Serratosa, M. P., & Merida, J. (2013). Pyranoanthocyanin derived pigments in wine: structure and formation during winemaking. Journal of Chemistry, 2013.
https://pdfs.semanticscholar.org/cd57/2
500e84efc56796a06cd4e01bd92daf334d0.pdf?_ga=2.178481440.544994986.1655538324-2028704915.1655538324 

27. Nguyen, T. (2016). Vitisins: Pyranoanthocyanins resulting from the addition of pyruvic acid or acetaldehyde to anthocyanins, contributing to wine color and color stability. Waterhouse Lab. Retrieved June 23, 2022, from waterhouse.ucdavis.edu/whats-in-wine/vitisins

28. Rentzsch, M., Schwarz, M., Winterhalter, P., & Hermosín-Gutiérrez, I. (2007). Formation of hydroxyphenyl-pyranoanthocyanins in Grenache wines: Precursor levels and evolution during aging. Journal of Agricultural and Food Chemistry, 55(12), 4883-4888.  Retrieved from: www.academia.edu/3552827/Formation_of_Hydroxyphenyl_pyranoanthocyanins_in_Grenache_Wines_Precursor_Levels_and_Evolution_during_Aging

29. Angulo, M. (2016). Hydroxycinnamates: Nonflavonoids important in juice and white wine. Waterhouse Lab. Retrieved June 23, 2022, from https://waterhouse.ucdavis.edu/whats-in-wine/hydroxycinnamates

30. Merkytė, V.; Longo, E.; Windisch, G.; Boselli, E. Phenolic Compounds as Markers of Wine Quality and Authenticity. Foods 2020, 9, 1785. 
https://doi.org/10.3390/foods9121785|

31. Darias-Martin, J., Martin-Luis, B., Carrillo-Lopez, M., . Lamuela -Raventos, R., Diaz-Romero, C., & Boulton, R. (2002). Summary 50: Effect of caffeic acid on the color of red wine. University of California Davis Viticulture and Enology. Retrieved June 23, 2022, from https://wineserver.ucdavis.edu/sites/g/files/dgvnsk2676/files/research-summaries/50%20caffeic%20acid%20and%20color.pdf

32. Beaver, J. (2016). Stilbenoids: Non-flavonids important as phytoalexins. Includes resveratrol. Waterhouse Lab. Retrieved June 23, 2022, from waterhouse.ucdavis.edu/whats-in-wine/stilbenoids

33. Zoecklein, B. W. (n.d.). Barrels, Barrel Adjuncts, And Alternatives Section 3. Retrieved June 23, 2022, from www.apps.fst.vt.edu/extension/enology/downloads/wm_issues/Barrels/Barrels%20-%20Section%203.pdf

34. Esparza I, Moler JA, Arteta M, Jiménez-Moreno N, Ancín-Azpilicueta C. Phenolic Composition of Grape Stems from Different Spanish Varieties and Vintages. Biomolecules. 2021 Aug 16;11(8):1221. doi: 10.3390/biom11081221. PMID: 34439886; PMCID: PMC8392641.

35. Oak Solutions Group. (2004). Oak Powder and Application Rates. Oak Solutions Group. Retrieved June 23, 2022, from https://oaksolutionsgroup.com/oak-powder-and-application-rates/ 

36. StaVin. (2005). Oak Oxygenation. StaVin.  www.stavin.com/stavin_oak_oxygenation.pdf 

37. StaVin. (n.d.). Liquid Tannins. StaVin. Retrieved June 23, 2022, from www.stavin.com/liquid-tannins/

38. ETS Laboratories. (n.d.). Wine Analysis. ETS Laboratories - Wine Analysis. Retrieved June 5, 2022, from www.etslabs.com/analyses/%23JGEXTB

39. Lueck, S. (2020). Introduction to Wine Phenolics [Film]. Institute for Enology & Viticulture at Walla Walla Community College. www.youtube.com/watch?v=uIJUh8nma-E