White wine is (almost always) made from white grape varieties...although it is technically possible to make white wine from red grapes if one acts quickly and removes the colouring element (i.e. skins) from the clear juice in timely fashion. Fermentation is generally at a lower temperature than that for red wine. Components to think about when tasting white wine are fruit concentration, acidity and alcohol (tannin comes from the skin of the grape so there are generally very low levels of it in white wine).
