Grape skins contain pigment and tannin. Red wine is always fermented with the skins present unless you talk about Champagne or sparkling wines containing red varietals. Tannin forms the structure and backbone of a wine and also the natural preservation and aging potential. Not all varietals have the same amount of tannin in their skin. Cabernet Sauvignon is more tannic than Pinot Noir. Red wines are fermented at a temperature of 75 to 85 degrees farenheit to extract color and tannin from the skin.