Phenolic content in wine
These include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine.
[2] During the growth cycle of the grapevine, sunlight will increase the concentration of phenolics in the grape berries, their development being an important component of canopy management.
[5] Most wine phenols are classified as secondary metabolites and were not thought to be active in the primary metabolism and function of the grapevine.
Vitis vinifera, the common grape vine, from which European style wines are made the world over, produces many phenolic compounds.
These phenols, mainly derived from the stems, seeds and skins are often leached out of the grape during the maceration period of winemaking.
In white wines the number of flavonoids is reduced due to the lesser contact with the skins that they receive during winemaking.
Wine grapes facing too much sun exposure can see an accelerated ripening period, leading to a lessened ability for the synthesis of flavonols.
[8] Some viticulturalists will use measurement of flavonols such as quercetin as an indication of a vineyard's sun exposure and the effectiveness of canopy management techniques.
[10] In the mid-20th century, French ampelographers used this knowledge to test the various vine varieties throughout France to identify which vineyards still contained non-vinifera plantings.
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.
These molecules will link up to create polymers that eventually exceed their solubility and become sediment at the bottom of wine bottles.
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 skin extracts contain four monomers (catechin, epicatechin, gallocatechin and epigallocatechin), as well as procyanidins and prodelphinidins oligomers.
[18] Commercial preparations of tannins, known as enological tannins, made from oak wood, grape seed and skin, plant gall, chestnut, quebracho, gambier[19] and myrobalan fruits,[20] can be added at different stages of the wine production to improve color durability.
The idea is that "riper" tannins will taste softer but still impart some of the texture components found favorable in wine.
This process can be accelerated by exposing the wine to oxygen, which oxidize tannins to quinone-like compounds that are polymerization-prone.
The winemaking technique of micro-oxygenation and decanting wine use oxygen to partially mimic the effect of aging on tannins.
[16] A study in wine production and consumption has shown that tannins, in the form of proanthocyanidins, have a beneficial effect on vascular health.
[18] Commercial preparations of tannins, known as enological tannins, made from oak wood, grape seed and skin, plant gall, chestnut, quebracho, gambier[19] and myrobalan fruits,[20] can be added at different stages of the wine production to improve color durability.
Tannins 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.
Many wine lovers see natural tannins (found particularly in varietals such as Cabernet Sauvignon and often accentuated by heavy oak barrel aging) as a sign of potential longevity and ageability.
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.
[24] In red grapes, the main flavonol is on average quercetin, followed by myricetin, kaempferol, laricitrin, isorhamnetin, and syringetin.
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.
[31] Resveratrol produced by grape vines provides defense against microbes, and production can be further artificially stimulated by ultraviolet radiation.
Trace amounts of vanillin are found naturally in grapes, but they are most prominent in the lignin structure of oak barrels.
[50][51][52][53] Limited preliminary research indicates that wine polyphenols may decrease platelet aggregation, enhance fibrinolysis, and increase HDL cholesterol, but high-quality clinical trials have not confirmed such effects, as of 2017.
