I had to wander around in the Cabernet vines for a while, with the Vinodogs in tow, before I found a red leaf amongst the canopy to photograph. I actually found three, all obscured by their surrounding yellowing leaves, but this one was the most red. The reds, oranges, and yellows we see in autumn foliage are due to a group of natural chemical/phenolic compounds called anthocyanins, carotenoids, and xanthophylls respectively. The red, with which this post is mainly concerned, comes from the pigment found in anthocyanins.
Anthocyanins are valuable to plants giving fruit shades of red, purple and blue (cyan, like one of the ink cartridges we periodically replace in our inkjet printers). Anthocyanins also provide photoprotection for plants whilst attracting pollinating insects (not necessary for grapevines of course), birds and other grape-munching creatures that can aid in the dispersal of seed. And, of course, it’s anthocyanins we see in all their glory each autumn as the leaves on deciduous trees change colour before dropping.
The thing with grapevines, though, is that it is the grapes that are supposed to change colour, not the leaves. Grape clusters begin to change colour with the onset of veraison with red varieties deepening to their characteristic purple. The grapes are also undergoing other complex changes that are not visible to the eye, but that result in an accumulation of sugars and other desirable compounds prized by winemakers and wine-imbibers alike.
The anthocyanin content in a wine ranges from zero in a variety devoid of skin pigment (e.g. Pinot blanc versus Pinot noir), to a maximum of about 2,500 to 3,000 mg/kg in a teinturier variety, such as Alicante Bouschet. In a good glass of Cabernet sauvignon, like a glass of wine from the vine in the above photograph, one could expect an anthocyanin content of about 890 mg/kg. I am not a chemist, so I am not going to get into how the pigment in grape juice is influenced by acidity, pH, tannin, flavones, co-pigments, iron and other metals - not to mention a dozen environmental factors. The main anthocyanin (not to be confused with anthocyanidins, their dietetic counterparts) in most V. vinifera varieties is malvidin-3-monoglucoside. I know, it's hard for me to pronounce too. But, unless you are a winemaker, the actual knowledge that anthocyanins are anthocyanidins that have been modified by the attachment of a molecule of glucose matters little. What matters most to the average wine-lover is the beautiful purple-blue hue that one espies in the miniscus of the young wine about to be consumed from one's glass.
The thing with grapevines, though, is that it is the grapes that are supposed to change colour, not the leaves. Grape clusters begin to change colour with the onset of veraison with red varieties deepening to their characteristic purple. The grapes are also undergoing other complex changes that are not visible to the eye, but that result in an accumulation of sugars and other desirable compounds prized by winemakers and wine-imbibers alike.
The anthocyanin content in a wine ranges from zero in a variety devoid of skin pigment (e.g. Pinot blanc versus Pinot noir), to a maximum of about 2,500 to 3,000 mg/kg in a teinturier variety, such as Alicante Bouschet. In a good glass of Cabernet sauvignon, like a glass of wine from the vine in the above photograph, one could expect an anthocyanin content of about 890 mg/kg. I am not a chemist, so I am not going to get into how the pigment in grape juice is influenced by acidity, pH, tannin, flavones, co-pigments, iron and other metals - not to mention a dozen environmental factors. The main anthocyanin (not to be confused with anthocyanidins, their dietetic counterparts) in most V. vinifera varieties is malvidin-3-monoglucoside. I know, it's hard for me to pronounce too. But, unless you are a winemaker, the actual knowledge that anthocyanins are anthocyanidins that have been modified by the attachment of a molecule of glucose matters little. What matters most to the average wine-lover is the beautiful purple-blue hue that one espies in the miniscus of the young wine about to be consumed from one's glass.
So, raise a glass of a little something luxuriously red (a squid ink black Petite sirah, perhaps?) and join me in a toast to the attributes of the not-so-lowly anthocyanin.
