Why is red wine red?

Here is a surprising fact: if you squeeze a handful of red grapes, the juice that comes out is almost colourless. So where does all that beautiful crimson colour come from? The answer lies in the skins.

Red wine gets its colour from pigments called anthocyanins, which live in the skin cells of dark-skinned grapes. During winemaking, the grape juice is left to soak with the skins in a process called maceration. As alcohol is produced during fermentation, it acts as a solvent and pulls the pigments out of the skins and into the juice. The longer the juice stays in contact with the skins, the deeper the colour.

This is exactly why rosé is pink rather than deep red — it spends only a few hours to a couple of days in contact with the skins, compared to one to four weeks for a full-bodied red. And it is how Champagne producers make white sparkling wine from red Pinot Noir grapes — by pressing the grapes gently and separating the juice from the skins immediately.

Different grape varieties have very different amounts of anthocyanin. Pinot Noir, with relatively thin skins, produces lighter-coloured wines (200-400 mg/l of anthocyanins). Tannat, one of the most deeply coloured varieties in the world, can contain over 1,500 mg/l.

As red wine ages, its colour changes. Young wines are vivid purple; middle-aged wines shift to ruby; and old wines turn brick-orange or even tawny. This happens because the anthocyanin molecules gradually bond with tannins to form larger, more stable compounds — and eventually some of these settle as sediment at the bottom of the bottle.

So the next time you admire the colour of a red wine, you are looking at a snapshot of its age, grape variety, and winemaking style — all in a single glance.