What are Tannins in Wine?

Tannins are a subject often mentioned by folks in the wine business, especially in tasting notes and around winery tasting rooms.  Because a number of visitors to the 4.0 Cellars tasting room ask about tannins, it seemed appropriate to address these interesting and somewhat mysterious molecules that appear to be important to wine.  So, here is my story on “What are Tannins in Wine?”

Tannins are molecules included in the category of polyphenols that tend to bind to and precipitate various other molecules like proteins, amino acids, and alkaloids from aqueous solutions, like wine.  (There goes some chemistry! LOL)  The name tannin refers to the use of molecules extracted from wood, like oak, to help soften animal hides (tanning leather).  The term tannins cover a wide range of polyphenolic molecules with different structures, yet having common chemical properties.  Below is a structural representation of a typical simple tannin molecule for any of you that may be interested.  Those -OH, or hydroxy functions attached to the aromatic ring are key to the properties of tannins.  (Damn, more chemistry!) 

 

 

 

 

Now, what do tannins have to do with wine?  These polyphenolic molecules originate in grape leaves and seeds.  When making white wines, pressing the juice away from grape clusters normally leaves the skins and seeds out of the fermentation process, thus producing very little tannin character in the wine.  When making red wines, because almost all of the color in a grape is in the skins, grapes are crushed and the juice fermented in contact with the seeds and skins.  This will, of course, allow for tannins to be extracted into the wine.  That is why red wines will invariably have more tannins than white wines. 

One important part of making red wines is the eventual separation of juice (wine) from the skins and seeds used in fermentation.  At the end of a fermentation, the skins and seeds usually drop to the bottom of the tank or vessel, and the wine above is drained or racked away from the solids (this is the free-run wine).  These solids, however, still contain a lot of wine, so the winemaker will press these skins and seeds to get the press-wine fraction.  This press-wine will naturally have more tannins than the free-run wine.  And, it is important to gently press these solids so that grape seeds are not crushed, thus releasing extremely bitter tannins. 

What do tannins taste like?  Tannins cause wine to taste dry, astringent, and even somewhat bitter.  You will feel these taste sensations mostly on the middle part of your tongue and in the front part of your mouth.  Too much tannin can be a bad thing, while the right amount of tannin is critical to a well-balanced wine.  Tannins are also important for aging wines as they act as antioxidants in much the same way as Vitamin E.  This is a key reason red wines tend to age better and for longer than white wines.  This is also part of the reasoning that drinking wine, especially red wine, is good for your health.  Yippee! 

Tannins can be experienced from other foods and drinks.  Probably the best example is unsweetened black tea which contains a large dose of tannin.  Other examples include high cocoa-content dark chocolate and whole nuts (almonds, walnuts, etc.). 

Some white wines do exhibit tannins in their flavor profile, most often due to fermentation or aging in oak barrels.  Remember the oak extracts that help to tan leather?  Well, oak tannins can have a significant influence on both white and red wines when oak barrels or oak alternatives are used in wine production and aging. 

Hopefully this simple treatise will help answer at least some of the questions about what are tannins and how do they get into my wine.