Water-soluble plant dyes, which are found in almost all higher plants and give the flowers and fruits their red, violet, blue or blue-black colour. They belong to the group of phenols (polyphenols), as well as to the large group of flavonoids, which comprises more than 6,500 species. The name is derived from the Greek terms anthos (flower) and kyáneos (dark blue). Anthocyans are the glycosides (sugar compounds) of the sugar-free anthocyanidins, the actual colouring components. The attached sugar molecules (glycones) make the colour pigments soluble in water. About 250 different anthocyanins are known. In wine these are mainly the glycosides of cyanidine, dolphinidine, malvidine, peonidine and petunidine.
The colours of anthocyanins are strongly dependent on the pH value. In an acidic environment the red colouring predominates, in an alkaline environment mainly blue and violet tones are found. Anthocyanins are sensitive to light and temperature and susceptible to higher pH values - they are most stable below 3. At pH values between 6 and 7 they are present as flavenols and are rather blue, between 7 and 8 they are purple. At pH values above 8 the molecule is converted to a yellow chalcone. The anthocyanins of the grape form during the véraison, when the green grapes turn dark. In most varieties, the colorants are formed exclusively in the skin of the grape. Only with the Teinturiers (dyer's grapes) is also a part contained in the then dark fruit flesh.