The polyphenols in wine refers to the phenolic compounds - natural phenol and polyphenols found in wine, which include a group of over a hundred chemical compounds which affect; colour, taste and texture of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins).
This large group of natural phenols can be separated into two broad categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the colour and texture of wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
Phenolic compounds comprise a diverse group of metabolites (small molecules) which are present in both grapes and wine. The phenolic content and composition of wine is greatly influenced by the vinification practice used on the grapes. During the handling and maturation of wine grapes several chemical changes may occur with the appearance of new compounds and possible disappearance of others.
There are four main groups of flavonoids: catechins, flavonols, anthocyanins, and tannins. Natural phenols are not evenly distributed within wine grapes. Phenolic acids are largely present in the pulp, anthocyanins and stilbenoids in the skin, and other phenols (catechins, proanthocyanidins and flavonols) in the skins and seeds. During the growth cycle of the grape, sunlight will increase the concentration of phenolics in the berries, along with appropriate canopy management. The proportion of the different phenols in bottled wine will therefore vary according to the different types of vinification. There are over 150 phenolic compounds found in wine.
Red wine will be richer in phenols, which are abundant in the skin and seeds, such as anthocyanin, proanthocyanidins and flavonols (along with phenols from the grape pulp). Whereas the phenols in white wine will essentially originate from the pulp in the grape, and these will be the phenolic acids together with lower amounts of catechins and stilbenes.
Wine phenols develop further during aging, transformed into complex molecules formed notably by the condensation of proanthocyanidins and anthocyanins, which explains the change in a wines colour. Anthocyanins react with catechins, proanthocyanidins and other wine components during wine aging to form new polymers resulting in a change of lower astringency on the palate. The ‘average’ total polyphenol content in wine - measured by the Folin-Ciocalteau method is 210 mg/100 ml for red wine and 30 mg/100 ml for white wine. The average content of phenols in a Rosé will fall in-between that found in red and white wines, depending upon varietal used and colour.
During the winemaking process - maceration or ‘skin contact’ is used to increase the concentration of phenols in wine. The use of oak aging can also introduce phenolic compounds, most notably vanillin which adds vanilla aromas. Flavonoids are the most abundant polyphenols in one’s diet. Tannins in red wine contain some flavonoid polyphenols, and in the first years as a red wine ages, research has shown that some of these polyphenols can help prevent cardiovascular diseases and some cancers, among other health benefits. But please consult your health professional before changing your diet.