Function

Grape skins are a vital part of the wine making process. While the fruit is growing, the skins protect the soft inner fruit. They are also packed full of polyphenolic compounds known as tannins, which give red and blush wines their color. Grape skins also become covered in yeast, which aids in the fermentation of the wine.

Whites

White wine is made from the flesh of white or black grapes. Prior to fermentation, the grapes are smashed to create juice, which partially removes the skin, which is then skimmed off so that it will not affect the wine color.

Reds

Red wine is made from crushed red grapes. When the grape is smashed, the skin floats to the top and is left with the juice during fermentation. The tannins and color compounds in the skins turn the wine red during this process.

Blush

Blush wine is made from the flesh of black grapes. The inner fruit of the black grape is grey, but after the process of smashing the grapes, a small amount of reddish pigment and tannins from the skins is left behind to add color and flavor.

Filtration

The filtration process removes skins, seeds and any remaining stems from the wine. In making red wine, the wine is not filtered until after fermentation. White wines and blush wines have most of their skins skimmed from the juice prior to fermentation.

Source:

WineGeeks: Wine Basics

Wineanorak: Tannins