The Science Behind Tannins

Tannins, organic polymerising-compounds which form in the skins and seeds of grapes, are one of the most important, and one of the most miraculous, aspects of wine. The grape produces them as a defence against the corrosive effects of oxygen, and it is this property which makes them so essential. Tannins keep the grape-juice from turning sour before fermentation can take place. Once the wine has fermented and is ageing in barrel or bottle, tannins maintain the structure of the wine over long periods of time.

Gradually the tannins begin to polymerise, clumping into larger particles (and trapping oxygen in the process) to sink to the bottom of the bottle, forming sediment. After sufficient time has passed, the wine will begin to oxidise as the tannins are no longer there to protect it. The colour of the wine will turn brown with age, a process which takes place faster for white wines with less tannins to protect them (yes there are tannins in white wine as well.) Hopefully, however, the wine will be opened long before this happens, at which point the tannins will transfer their anti-oxidant properties to the drinker. It is the tannins which also make the occasional glass of red wine a positive health-choice. There is evidence tannins are useful in preventing high levels of cholesterol and thanks to their natural antioxidant qualities, they also help reduce the negative effects of free radicals.