WHAT ARE TANNINS?
Virtually all families of plants, including wine grapes (Vitis vinifera) have “tannins”.
Tannins are a group of phenol compounds found in most plants called “polyphenols”. These polyphenols are, for the most part, soluble in water, and therefore are largely responsible for giving wine a defined structure or body, adding balance, complexity and structure, as well as acting as a preservative to enable a wine to age longer.
While tannins exist naturally in the grape skins, stems and seeds as well as oak used for wine barrels, the tannins that develop in wine are actually very different. This is because the chemical make-up of the tannins actually changes during the various process during both the winemaking process as well as aging.
Even though tannins don’t have any smell themselves, they are also indirectly responsible for a wine’s aroma. In slowly reacting with the wine’s alcohols and esters (acidic alcohols), they gradually erode the initial flowery, fruity aromas found in young wine thus enabling the “toasted oak” notes from the barrel aging process.
Tannins also affect the colour of red wine. The bluish-red or violet colour of a young red wine formed by the pigments in the grapes are gradually replaced by deeper, brick-red or dark cherry colours created as long polymer chains linking the grape pigments to the tannins.
The term ‘tannin’ comes from the ancient practice of using extracts from plants to cure leather (the process still 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, and 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.
There are two main types of tannins: hydrolyzable tannins and non-hydrolyzable tannins (also called “Proanthocyanidins”). Hydrolyzable tannins (meaning that they are able to be split up and broken down by interacting with water) are commonly found in acidic form in the bark and wood of oaks and other plants, or more specifically, the oak barrels used for ageing wine. Non-hydrolyzable tannins are often found in other plant sources such as tea, pomegranates as well as grape seeds and grape skins.
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, even in young red wines with “younger tannins”.
White wines have much lower tannin levels because white wines are not typically fermented with their skins or seeds as in red wine production, so the extraction of tannins is minimal. In contrast, the ability to age white wine derives primarily from acidity, but also from the alcohol content and fruit extracts.
Learn more about the effects of aging on tannins on our Ronda Wine Tour, as well as the differences between French and American oak!