The next time you buy a bunch of red (officially black) grapes, peel off the skin and you will see that the flesh is almost colourless. Red wine gets its colour from a pigment known as anthocyanin that is found in grape skins. Hence it is possible to make white wine from red grapes by separating the juice from skins as soon as the grapes are crushed. Only a few red grapes have coloured flesh; these are known as teinturier varieties.
To make a red wine the juice and skins are macerated together for days and sometimes weeks to extract colour and tannins. This can happen before, during and after fermentation. The colour depends on several factors, including the length of maceration, and how often the winemaker pumps the solids over the juice.
The grape variety can also make a big difference. Some thick-skinned, deeply coloured grape varieties such as Malbec and cabernet sauvignon give a lot of colour to a wine. Others, such as pinot noir and garnacha, have thin pale skins so the wines tend to be light in colour.
Wines lose colour as they age, typically starting out purplish or deep red, gradually becoming paler, turning garnet and then brick red. Some of the anthocyanins precipitate forming chains or sediment, which is why some wines need decanting.
We tend to assume that deeply coloured wines are higher in quality, although the two are unrelated. Many producers, particularly in California, add grape concentrate (usually made from those teinturier varieties) to their wine, giving it more colour and making it taste more rounded.
