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Wine and Colour

The colour in wines varys depending on not least whether its a red or a white wine.  The key things that influence the colour of wine are; grape variety, wine making process and the age of the wine.

The two parts are

Red Wine colour

For red wine the skin colour of grapes is determined by the type and the amount of anthocyanins. These chemicals are found in the skins of most grapes and are particularly found in the skins of most red grapes. Strangely most red wine grape varieties are not red but bluish or even black such as cabernet sauvignon or pinot noir. Occasionally other colours exist such as crimson for grenache.

Once the grapes have been harvested and the berries crushed, the juice and skins are mixed. Grape varieties with small berries and or thick skins will have more skin to juice, compared to bigger berries or thin skin varieties,  which will have more colour will come from them. Typically most of the colour is extracted as the juice is fermented.  This is becuase fermentation increases the temperature and alcohol content in the juice, both of which help to extract the colour from the skins.

The anthocyanin colour from the skins reacts very quickly and becomes bound up with tannins to form Pigmented Tannins which are far more stable than the red anthcyanin. Pigmented Tannins  can have a range of colours from orange to purple, but each colour is more or less stable with blue and purple colours more likely to react and become colourless. As a result often young wines  have a purple tinge which will  fade to a bricky red as they age.  Eventually the red Pigmented Tannin fades leaving a brown or mahagony colour. Not only do the wines fade, because chemicals fade, but also the depth of colour will fade. Pigmented Tannins polymerise forming larger chains ( Polymerisation is where molecules chunk together to form big chains). Eventually,  the large molecules get so large that they precipitate out of the wine and form the sediment in the bottles of wine. As they leave the wine the colour intensity fades over time. Surprisingly wines that have been exposed to oxygen during fermentation or during some subsequent aging will form more stable Pigmented Tannins, making the wine less likely to fade over time.

So the colour of the wine can give an idea of the maturity of the wine and the depth of the colour gives an idea of the skin contact.

White wine colour

While red wines can occasionally be red, white wines are never white. Very young wines can be clear, or green and pale straw golden or amber are also common. Unlike red wines which get their colour from leaving the juice in contact with the skins. White wines are usually separated quickly from the skins. As such,  many of the colour giving anthcyanins are not passed to the juice. That’s not to say that colour is not absorbed by white wines. (remember something is red because the red colour absorbs all colours except red which is reflected). But white wines tend to absorb light in the UV spectrum (beyond what our eyes can see) with the other colours simply passing through the wine neither absorbed or reflected hence making it clear.

That is not to say all white wines are clear or even stay clear. They can contain a small amount of colour giving phenolics. Like red wines they do tend to change over time. For example, young Riesling can have a green tinge when young but can turn golden and eventually amber as the wine oxidises and the phenolics polymerise (that is join together in chains).  The acidity in the wine has an effect on the colour and low pH and high So2 levels tend to bleach the wine keeping it clearer for longer.

Wines do take on colours from barrels, particularly if aged in the barrel after fermentation. The colour and other phenolics, such as tannins leech from the barrel into the wine, turning the wine golden in colour. This is similar to clear whiskey turning brown in a barrel over time. Strangely, if the wine is fermented in the barrel the yeast will absorb the pigments which are then locked up in the lees (dead yeast), resulting in a lighter shade than if the wine were fermented in stainless steel and then aged in the colour giving barrels.