Structural Stability

Anthocyanins are almost always stored as glycosides (see glycoside section for further information) since the glycoside-lacking anthocyanidins are very unstable and can rapidly convert into other colourless forms, reversibly and irreversibly. Together with a range of different sugars and various acyl-groups (fancy name for acids) attached to different positions in a myriad of combinations, several hundred different anthocyanin forms are produced by plants. The structure of anthocyanins, the presence of various other compounds (particularly co-pigments, fancy name for compounds that can interact physically with anthocyanins) and the pH of the solution that they are in, all have an impact on colour absorption and hence colour perception. For example, wines with a pH closer to 3 than 4 have a bright red colour whilst wines with a pH close to or above 4 have an apparent colour that more closely resembles purple or even blue! (Late harvest monster Shirazes for example….).