🍷 Anthocyanins

Anthocyanins are the highly coloured compounds responsible for the colour of red grapes, according to the Australian Wine Research Institute (AWRI). In wine they are called free anthocyanins and are found in grape must, ferments and young wines.

Free anthocyanins are not very stable under wine conditions, so their contribution to wine colour decreases quite rapidly as the wine ages. They are bleachable by sulfur dioxide (SO2). During fermentation and storage they react with tannins to form pigmented tannins. These are stable coloured compounds that are not bleached by SO2 and have been shown to contribute up to 90% of the colour of red wine after two years' storage.

Anthocyanins are extracted from the grapes during fermentation. An AWRI review notes that extraction occurs rapidly up to day four or five, with little further increase after day 10. In extended post-fermentation maceration, in which skins, seeds and any stalks stay in contact with the wine, the anthocyanin concentration in the wine decreases, mainly because anthocyanins are incorporated into pigmented tannins.

This explains the change of colour with age: young red wines are purple because of monomeric anthocyanins, while aged wines show orange and brick red tones caused by anthocyanin-derived polymeric pigments forming over time.