Red wine is created by extracting the colour from the skins of grapes by a process of maceration. Virtually all red grapes have clear juice and it is technically possible to make white wine from dark-skinned varieties. To make red wine, red grapes are (usually) crushed and fermented with the skins, the fermented liquid then being left for a further period in contact with the skin pulp. The main considerations when tasting red wine are fruit concentration, acidity, alcohol and tannin.