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. This is the taste sensation you experience after swallowing the wine. This aftertaste can be short or long depending on the intensity of a wine's flavor. Generally, the longer the aftertaste, the better the wine. This is called the wine's finish .