I have to admit, I never think about tannin when tasting white wine. However, a conversation with winemaker Steve Matthiasson the other night at our Thursday tasting got me thinking about just that. Tannins in wine come from the grape seeds, stems, and skins, as well as from the wooden barrels used for ageing. If overdone or unbalanced, tannins can cause a drying feeling or bitter sensation in your mouth (think over-steeped tea) but they have their purpose; they give a wine color, structure, and texture and help preserve the wine for age ability.
White wine juice spends significantly less time comingling with the seeds, skins, and stems because after the grapes are crushed (crushing, or cracking the grapes, releases the juice), grapes for white wine are pressed, leaving the skins behind before the juice is fermented in to wine. In fact, the main difference between making red and white wine is that fermentation for red wine takes place before the grapes are pressed (skins on) while for white wine fermentation beings after the grapes have been pressed (skins off.) Although white wine can be made from red grapes (think white Zin – if you must – or Pinot Noir and Pinot Meunier, two red grapes used to make Champagne), many white wines are made from grapes with white skins (well, actually kinda greenish but you get the picture.)
It is possible to leave the juice of white grapes in contact with the skins for a longer period of time to add some dimension to the wine. However, if left too long, or fermented with the skins on, which is rare, the result will most likely be a harsh, bitter white wine. Acidity, not tannin, is generally the component that adds dimension to white wines, preventing them from being too soft and giving them that sense of freshness.
Oak barrels, which are used for ageing most red, and some white, wines, also impart tannins to wine. There are tannins present in wood that can add structure, as well as flavors, to the finished wine. These ‘wood tannins’ tend to be softer than ‘fruit tannins’ -- from the skins, stems, and seeds – and generally wear down over time. Because wooden barrels are the most significant source of tannin for white wines, such as Chardonnay, the tannins are more subtle and therefore difficult to detect. In the end, it is pretty rare to be able to detect tannin in white wines, which is why wine tasters hardly discuss. I will, however, keep it in the back of my mind and know that it may be in there -- somewhere. Cheers!