A wine grape is a small but complex package. The skin contains pigments, tannins, and aromatic compounds. The pulp, which makes up most of the grape, is rich in sugar and acid — the two most important building blocks of wine. The seeds contain bitter tannins and oils that are rarely welcome in the wine.
Grapes used for wine production are almost exclusively of the species Vitis vinifera. They differ from common table grapes — they are smaller, sweeter, and more compact with thicker skins. It is precisely the thick skin and high sugar concentration that makes them so suited to creating well-structured, complex wines.