Vitis vinifera, the common grape vine, from which European style wines are made the world over, produces many phenolic compounds. There is a varietal effect on the relative composition.
Flavonoids or extended skin contact allows the extraction of phenolic compounds from the skins of the grape into the wine In red wine, up to 90% of the wine's phenolic content falls under the classification of
flavonoids. These phenols, mainly derived from the stems, seeds and skins are often leached out of the grape during the maceration period of winemaking. The amount of phenols leached is known as
extraction. These compounds contribute to the
astringency, color and mouthfeel of the wine. In white wines the number of flavonoids is reduced due to the lesser contact with the skins that they receive during winemaking. There is on-going study into the
health benefits of wine derived from the
antioxidant and
chemopreventive properties of flavonoids.
Flavonols Within the flavonoid category is a subcategory known as
flavonols, which includes the yellow
pigment -
quercetin. Like other flavonoids, the concentration of flavonols in the grape berries increases as they are exposed to sunlight. Wine grapes facing too much sun exposure can see an accelerated ripening period, leading to a lessened ability for the synthesis of flavonols. Some
viticulturalists will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques.
Anthocyanins Anthocyanins are phenolic compounds found throughout the
plantkingdom, being frequently responsible for the blue to red colors found in
flowers,
fruits and
leaves. In wine grapes, they develop during the stage of
veraison, when the skin of red wine grapes changes color from green to red to black. As the
sugars in the grape increase during
ripening so does the concentration of anthocyanins. An issue associated with climate change has been the accumulation of sugars within the grape accelerating rapidly and outpacing the accumulation of anthocyanins, in particular of
enocyanin, There are several types of anthocyanins (as the
glycoside) found in wine grapes which are responsible for the vast range of coloring from ruby red through to dark black found in wine grapes.
Ampelographers can use this observation to assist in the identification of different
grape varieties. The European vine family
Vitis vinifera is characterized by anthocyanins that are composed of only one molecule of
glucose while non-
vinifera vines such as
hybrids and the American
Vitis labrusca will have anthocyanins with two molecules. This phenomenon is due to a double mutation in the
anthocyanin 5-O-glucosyltransferase gene of
V. vinifera. 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. wine has a high pH level which means that there is a higher concentration of blue and colorless
anthocyanin pigments in the wine. The resulting wine's coloring will have more blue hues than bright ruby red hues. The color variation in the finished red wine is partly derived from the
ionization of anthocyanin pigments caused by the
acidity of the wine. In this case, the three types of anthocyanin pigments are red, blue and colorless with the concentration of those various pigments dictating the color of the wine. A wine with low
pH (and such greater acidity) will have a higher occurrence of ionized anthocyanins which will increase the amount of bright red pigments. Wines with a higher pH will have a higher concentration of blue and colorless pigments. As the
wine ages, anthocyanins will react with other acids and compounds in wines such as tannins,
pyruvic acid and
acetaldehyde which will change the color of the wine, causing it to develop more "brick red" hues. These molecules will link up to create
polymers that eventually exceed their
solubility and become sediment at the bottom of wine bottles. or during
controlled oxygenation processes during the
aging of wine.
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 by the
tactile sensation of
astringency and sense of bitterness that they can leave in the mouth. This is due to the tendency of tannins to react with
proteins, such as the ones found in
saliva. The management of tannins in the winemaking process is a key component in the resulting quality. In
food and wine pairing, foods that are high in proteins (such as
red meat) are often paired with tannic wines to minimize the astringency of tannins. However, many wine drinkers find the perception of tannins to be a positive trait, especially as it relates to mouthfeel. Tannins are found in the skin, stems, and seeds of wine grapes but can also be introduced to the wine through the use of oak barrels and chips or with the addition of tannin powder. The natural tannins found in grapes are known as
proanthocyanidins due to their ability to release red anthocyanin pigments when they are heated in an acidic solution. Grape extracts are mainly rich in monomers and small oligomers (mean degree of polymerization Phenols from oak ageing ==