Tannin is an astringent polyphenolic compound found mostly in the bark, leaves and immature fruit of a variety of plants. Tannin binds to proteins and other plant polymers to give it a bitter, astringent taste –that dry, pucker feeling when you drink red wine. The breaking down or modification of tannins plays an important role in the aging of wine. Wine tannins exist in the grape skins, stems and seeds, and their removal depends on the winemaking process used. Essentially, there is a chemical reaction during the winemaking process that changes the composition of the tannins.
Conventional wisdom teaches that during red wine aging, the tannins gets larger, become insoluble and fall out of solution over time. However, scientific data does not support this explanation, and what actually happens during aging is still uncertain. It could very well be that the tannins are breaking up in the acidic environment of the wine and are therefore getting smaller. Discovering the secrets behind the aging process would be valuable information, as aging is such a valuable component of the appreciation of fine wine.
The concentration of tannins in grapes reduces as the grape ripens and sugar levels increase. This is why unripe red grapes make nasty wines – the tannin concentration is so high that the wine turns out virtually unpalatable. With this in mind, researchers are trying to determine specific grape tannins that could be used as markers of quality in viticulture.
This all goes to show that tannin management is one of the keys to successful red winemaking. As there is still much to learn about the way in which tannins affect the end wine product, management is far from an exact science, and winemakers are left with little more than a trial-and-error method. In time, researchers will hopefully be able to provide valuable data on this complex group of chemicals to help winemakers and viticulturists make better informed decisions – the result being more complex and interesting red wines to enjoy!