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.
The colour of red wine varies according to the proportion of anthocyanins present. Cyanidine and dolphinidine give a colour that goes into the blue range. Malvidin-3-glucoside, which is most abundant in blue grapes (over 40%), causes deep red tones, which is why red wines made from blue grapes ultimately appear predominantly red. However, the amounts of individual anthocyanins in the berries are specific to the grape variety. The smaller the berries, the more intense the colouring. This is due to the fact that many small berries, often with thick skins, have more pigmented skin surface than fewer, but larger berries. The colour intensity also depends on the pH value of the wine. An acidic wine with a very low pH-value has an intense bright red colour, an acidic wine with a slightly higher pH-value has a darker colour from purple red to bluish. This phenomenon can be seen in many plants, such as roses and also other flowers, whose flower colour is determined by the acidity of the soil.
Oxidizing agents have a decolorizing effect on anthocyanins. Therefore too much sulphur dioxide in wine can cause the red colour to fade. Some anthocyanins are converted into proanthocyanidins (tannin derivatives) by metabolic processes in the grape. During bottle ripening or ageing of a wine, anthocyanins also react with the tannins and are precipitated as a deep red deposit (sediment). This thus causes the change and fading of the wine colour during the ageing process. The red component decreases, while the yellow component increases relatively. The red wine turns brownish and becomes lighter. Since each grape variety has a specific anthocyanin pattern, the colour profile can also be used to some extent for grape variety identification. This is done by chromatography and spectrometry of grapes or wine.
A specific anthocyanin derivative is malvidin 3,5-diglucoside, which is mainly found in the American wild vine Vitis labrusca. However, the designation "hybrid dye" or "direct carrier dye" is misleading because non-crossed and/or ungrafted labrusca vines also possess the dye. It gives the wine a typical orange-red colour. In the varieties of the European species Vitis vinifera this substance is not detectable. Although it has no negative influence on the taste and is also harmless to health, its presence proves that the grapes concerned contain American genes or that a wine contains parts of a wine made from such grapes. Within the EU, hybrids without shares of European genes may not be used for wine production (see quality wine grape varieties).
The INAO (Institut National des Appellations d'Origine) has established a special chromatographic method (HPLC) for the detection of malvidin 3,5-diglucoside with a maximum limit of 15 mg/l. However, the aim is to reduce it to a maximum of 2 mg/l for quality wines, but no agreement has yet been reached within the EU member states. In the new breeding of fungus-resistant varieties, resistant American vines have been used and thus malvidin 3,5-diglucoside genes have also been introduced into the varieties. These include Cabernet Carol, Cabernet Cortis, Medina (1), Monarch, Regent and Rondo. In the latter two varieties, the limit value of 200 to 300 mg/l is considerably exceeded. In Austria, since 2009, the quality wine test for the award of the national test number has been routinely tested for malvidin 3,5-diglucoside with the limit value of 15 mg/l. See a list of all wine ingredients under total extract.