When tasting wine, it's critical to hold it in your mouth long enough to taste all of the flavors. The first flavor to be detected is sweetness, or fruitiness. Sweetness comes from natural grape sugars and alcohol. This is called the wine's attack . The second flavor to be detected is sourness, or acidity.
Acidity serves to amplify and develop the fruity flavors initially tasted in the attack.
As these flavors develop, they become more pronounced and obvious. This is called the wine's evolution . As the neutralizing effects of our alkaline saliva begin to dissipate the effects of acidity, the final flavor to be detected is bitterness. Bitterness comes from tannins extracted from grape skins, stems and seeds, and from barrel aging. Tannins are what allow red wines to improve with age.