Water-soluble plant pigments that occur in many higher plants and give the flowers and fruits their red, violet, blue or blue-black colouring. They belong to the group of phenols (polyphenols), as well as to the large group of flavonoids, which number over 6,500 species. The name is derived from the Greek terms anthos (flower) and kyáneos (dark blue). Anthocyanins are the glycosides (sugar compounds) of the sugar-free anthocyanidins, the actual colouring components. The sugar molecules (glycones) cause the water solubility of the colour pigments. There are about 250 different anthocyanins. In wine, they are mainly the glycosides of cyanidin, delphinidin, malvidin, peonidin and petunidin.
The colours of anthocyanins are strongly dependent on the pH value (concentration of active acids). In an acidic environment, red colouring predominates; in a basic environment, blue and violet tones are most common.Anthocyanins are sensitive to light and temperature and susceptible to higher pH values - below 3 they are most stable. At pH values between 6 and 7 they are present as flavenols and tend to be blue, between 7 and 8 purple. At pH values above 8, the molecule is converted to a yellow chalcone. The anthocyanins of the grape are formed during the véraison (ripening of the berries), when the green grapes turn dark. In most varieties, the colouring substances are formed exclusively in the skin of the berries. Only in the case of the Teinturiers (colouring grapes) is a part also contained in the then typically dark flesh of the berries.
The colour of red wine varies according to the proportions of anthocyanins present. Cyanidin and delphinidin give a colour that goes into the blue range. Malvidin-3-glucoside, which is most abundant in blue grapes at over 40%, causes deep red hues, which is why red wines made from blue grapes ultimately appear predominantly red. However, the proportions of individual anthocyanins in the berries are grape variety-specific. The smaller the berries, the more intense the colouring. This is because many small berries with often thick skins have more pigmented skin surface overall 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 is intensely bright red, a wine with a slightly higher pH has a darker colour from purple to bluish. This phenomenon is seen in many plants, such as roses and also other flowers, whose flower colour is determined by the acidity of the soil.
Oxidising agents have a decolourising 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 age ing 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 in part 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 grape Vitis labrusca. The designation "hybrid dye" or "direct carrier dye" is misleading, however, because non-crossbred and/or ungrafted labrusca vines also possess the dye. It gives the wine a typical orange-red colour. This substance is not detectable in the varieties of the European species Vitis vinifera. Although it has no negative influence on the taste and is also harmless to health, it means that the grapes in question 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 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 lower the limit. However, efforts are being made to lower the limit to a maximum of 2 mg/l for quality wines, but so far no agreement has been reached within the EU member states. In the breeding of new fungus-resistant varieties, resistant American vines have been used and thus malvidin-3,5-diglucoside genes have also found their way into the varieties. These include Cabernet Carol, Cabernet Cortis, Medina (1), Monarch, Regent and Rondo. In the latter two varieties, the limit value is considerably exceeded at 200 to 300 mg/l. In Austria, since 2009, malvidin-3,5-diglucoside has been routinely tested for the limit value of 15 mg/l in the quality wine test for the award of the state test number. See a list of all wine constituents under Total extract.
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Markus J. Eser
Weinakademiker und Herausgeber „Der Weinkalender“