Sources and roles of phenolic compounds found in wine

Phenols are highly reactive chemical compounds of primary importance in the quality of red wines. Phenol, the basic building block, is an aromatic organic compound (formula C6H5OH) where the phenyl group (C6H5, where six bonded carbon atoms with alternating double bonds are connected to five hydrogen atoms) is bonded to a hydroxyl group (OH, where the oxygen atom is covalently bonded to an hydrogen atom). A graphical representation of a phenol is provided below.

Phenolic compounds are:

• Responsible for the color of red grapes and wine
• Involved in the oxidative browning of white wines
• Contributors to taste and astringency through interactions with salivary proteins
• Another measure of wine quality.

The two major classes of wine phenolic compounds are flavonoids (defined by a C6-C3-C6 skeleton consisting of two phenolic rings joined by a central, oxygen-containing ring -- Jackson) and nonflavonoids (possessing a C6-C1 or C6-C3 skeleton; all numbers following "C" are subscripts). The sources and roles of the phenolic compounds falling into these two classes are illustrated in the figure below and the relative concentrations of selected classes are provided in the table following.

Table 1. Generalized concentration of various phenolic compounds
present in wine

Phenolic	White Wine (mg/L)	Light Red Wine (mg/L)	Full Red Wine (mg/L)
Volatile	Trace	10	40
Hydroxycinnamic acids	150	200	200
Other nonflavonoids	25	40	60
Anthocyanins	0	200	400
Catechins	25	150	200
Polymeric catechins	0	600	900
Totals	200	1200	1800

Source: Kennedy, et al., Grape and wine phenolics: History and perspective,
AJEV, 57(3), September 2006.


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