What is the difference between red and white wine?

The colour comes from the skin of the grape and only ends up in the wine if the juice stays on the skins.

The Australian Wine Research Institute calls that week-long period the most important factor for the phenolic composition of red wine: how long skins, seeds and any stems stay in contact with the juice. The juice of almost all grapes is itself nearly colourless. Without skin contact you are therefore left with a light wine, even from a blue grape.

White wine is usually pressed before the juice can take anything from the skins and pips, and tannin is found precisely there.

The Australian Wine Research Institute describes the choice the winemaker has: press straight away, or first allow a period of skin contact. In trials this meant 6, 12, 24 or 72 hours. The longer that contact lasts, the more phenolics and malic acid end up in the juice. With red wine the same contact lasts days to weeks, and that is where the difference in tannin comes from.

Days to weeks, and there is no fixed number: in the specialist literature the steeping time ranges from a few days to two months or more.

The Australian Wine Research Institute itself tested periods of 21 and 60 days in 2018. How much comes out of the skins also depends on the variety and the year, because the grape must first have made those substances itself. Longer maceration is therefore not a dial that always turns the same way.

No, the European market organisation defines wine as one product, with no separate definition for red or white.

Annex VII of Regulation (EU) No 1308/2013 defines wine as the product obtained exclusively from the complete or partial alcoholic fermentation of fresh grapes or must. The actual alcoholic strength must be at least 8.5% in wine zones A and B and at least 9% elsewhere, with 15% as the upper limit and a number of exceptions. Colour plays no role in that definition; there are, however, separate categories such as liqueur wine and sparkling wine.

White wine from black grapes is possible, as long as the juice does not stay on the skins.

The juice of most dark grapes is almost colourless; the pigments are in the skin. Anyone who presses quickly and separates the juice straight away ends up with a light wine. The same logic explains rosé: short skin contact passes on part of the colour and leaves most of the tannin behind.