Anthocyanins are the most important natural colorants in grapes. Anthocyanins are a group of naturally occurring phenolic compounds that are responsible for the red, purple and blue colours found in many fruits, vegetables, flowers and wine grapes. They belong to a parent group of molecules called flavonoids; they are odourless and virtually have no flavour, contributing to taste a moderately astringent sensation.
Contributing little to the taste of wine, however anthocyanins readily polymerize with tannins, they play an important role in tannin retention in and aging. There is a close association between anthocyanins and into colour stability of wine. Anthoxanthins are clear, white to yellow counterparts of anthocyanins.

 

Due to their unique chemistry, anthocyanins are separated into five groups; cyanins, petunins, peonins, malvins and delphinins. The presence and concentration of these groups of anthocyanins is varietal specific and changes with variable environmental conditions and viticultural practices. The proportion of all five has a huge impact on the colour and colour stability in a wine.
Research has found that the total content of anthocyanins in conventionally grown grapes is significantly higher compared to that found in grapes grown organically. The accumulation of anthocyanins reached a maximum 28 days after veraison (also the period of highest temperatures), and then decreases until harvest.
Results also showed that grapes grown conventionally had higher proportions of these five groups of anthocyanins compared to grapes from organic plots. For each grape variety considered, climatic conditions and agronomic practices were important factors.
Anthocyanins also have several beneficial effects for humans including the reduction in the incidence of coronary heart disease, enhancement of visual acuity, maintenance of normal vascular activity, as well as anti-carcinogenic, anti-mutagenic, ant-inflammatory, and anti-oxidative properties. Consequently, the interest and identification of anthocyanins in red grapes and wine has increased considerably in recent years.
In leaves during photosynthesis; anthocyanins have been shown to act as a ‘sunscreen’, protecting cells from direct sunlight damage by absorbing blue-green and ultraviolet light rays, thereby protecting the tissues from photo-inhibition stress. These pigment molecules are effectively sunscreen for plants. In addition to their primary function, they also act as anti-oxidants, protecting plants from free radical oxidation. Anthocyanin synthesis is activated by direct exposure to UV radiation and is closely associated with veraison.
This is important because anthocyanins are found in high concentrations in the skins of black grapes and contribute to the colour of red wine. As if you kept the skins of red grapes separate from the juice, you could make white wine from red grapes; a processed used in the production of sparkling wines.