All wine, including white wines have grape tannins, though some are more tannic than others. Tannins are largely responsible for giving red wines a defined structure or ‘body’, so essentially the “skeleton” of any wine.
Tannins themselves are found principally in the bark, leaves and immature fruit of a wide range of plants. They form complexes with proteins and other plant polymers such as polysaccharides. Rather surprisingly, the term ‘tannin’ comes from the ancient practice of using extracts from plants to cure leather (the process referred to as ‘tanning’). This process exploits one of the key properties of tannins: they have a strong tendency to link up with a range of other chemical entities, most particularly proteins. When applied to animal hides for example, tannins cross-link the proteins, turning something rather soft and floppy into a material that’s tough and inert enough to make shoes, belts and saddles.
While tannins exist naturally in grape skins, stems and seeds, as well as wine barrels, the tannins found in wine are actually very different. This is because the chemical make-up of the tannins actually changes during the various process during winemaking and aging. Higher tannin wines tend to bottle age better than those that have fewer tannins, and these tannins will actually gradually ‘soften’ over time. So go ahead and save that Cab for a few years! Older vintages are also better if you’re prone to headaches from drinking wine.
White wines have much lower tannin levels because white wines typically aren’t fermented with their skins or seeds as in red wine production, so the extraction of tannins is greatly reduced. In whites, the ability to age derives primarily from acidity, but also from alcohol and fruit extracts.
Tannins are also one reason why it is recommended that you allow a wine to ‘breathe’ or aerate before drinking it. The air softens the tannins, particularly in young red wines.