Phenols (polyphenols) are a group of water-soluble plant dyes with over 6,500 different species. They are found in fruits, flowers and leaves of plants. The flavonoids were discovered in the 1930s by the Nobel Prize winner Albert von Szent-Györgyi Nagyrapolt (1893-1986) and were initially called vitamin P. The name is derived from Latin Flavus (yellow), because flavonoids often, but not always, have a yellow colour. Most flavonoids are bound to the sugar types glucose or rhamnose, which are then called glycosides. The flavonoids are divided into seven groups: anthocyanidins (anthocyans), flavones, flavonols, flavanols, flavanonols and isoflavones.
Types found in grapes include the group of anthocyanidins(cyanidin, dolphinidin, malvidin, peonidin, petunidin), catechin and fisetin in dark (blue to black) grapes, and quercetin in light (white) grapes. Many flavonoids have a positive effect because a large part is not absorbed and reaches the large intestine. Due to their antioxidant properties, they have various health-promoting effects on inflammations, histamine allergies and cramps, as well as inhibiting cancer cells and viruses. The second large group of plant dyes found in grapes are the carotenoids (for yellow, green, pink, red).