If red wine is your preference, you know the various characteristics associated with its flavor profile. Unless you’re going with a sweet red, you will likely encounter some bitterness and astringency not associated with white wine. Whether it’s soft and sweet or aggressive and dry will depend on the naturally-occurring tannins in the wine.

Tannins are substances found within plants, seeds, bark, leaves, and fruit skins that serve as a defense mechanism against predators. They are a polyphenol and are known for imparting a bitter and astringent taste.

In wine, tannins come from grape skin, grape seeds, and from aging in oak barrels. The longer the juice is exposed to these things, the more tannins there will be in the flushed wine. Since white wines do not ferment with the grape skin and seeds like red wine, they naturally have fewer tannins. To achieve a dry white wine, such as a chardonnay, winemakers can age the wine in oak barrels because the wood naturally contains tannins.

What does tannin taste like?

Tannins add bitterness and astringency and also make for a more complex wine. While both bitterness and astringency are caused by tannins binding with proteins in saliva, they are not the same characteristic. Bitterness is one of the five basic flavors and is the sharp/acidic flavor found when drinking wine. Astringency, on the other hand, is what gives you that “dry” mouthfeel when drinking certain wines. It’s less a flavor and more of a sensation. When the tannins bind with salivatory proteins, it essentially eliminates the lubricating proteins in the mouth.

Red wines are not the only common high-tannin food/beverage you may frequently encounter. Unsweetened black tea is essentially pure tannin dissolved in water. Dark chocolate, cinnamon, pomegranates, red beans are just a few other examples. That dry sensation you feel in the middle of your tongue? That’s from tannin.

Benefits of tannins

While a high presence of tannins may not be everyone’s cup of tea (or wine), they benefit the wine beyond a complex flavor profile. One benefit of tannins is they act as a fining agent for the wine. Tannins bind to and precipitate haze-causing proteins, resulting in more clarity. For high-tanning wine, protein stability is, therefore, not a concern.

While wine clarity and protein stability are nice bonuses, they are not the main benefit of tannins. The single most important advantage of tannins is as a natural antioxidant. While most wines are best when enjoyed only a few years after they’ve been bottled, red wine’s aging potential is largely dependent upon tannin content. Tannins bind to oxygen to protect the wine from the effects of oxidation; less dissolved oxygen content means there is less oxygen to turn phenolics into browning compounds and alcohol into acetaldehyde.

You can essentially think of tannin as a natural wine preservative.

Despite their benefits, an overabundance of tannin can lead to an unpleasant drinking experience. There are a few ways to “tame” tannins, such as with fining agents and by readjusting wine balance. Wine can be better balanced by tweaking its sugar and acid contents. A general rule of thumb is higher tannin content is more acceptable when acidity is low, and the alcohol content is high. If both the tannin content and acidity are high, it will result in a hard and astringent wine. You can learn more about wine acidity here. 

Sources:

https://winemakermag.com/technique/1045-tannin-chemistry-techniques

https://winefolly.com/review/what-are-tannins-in-wine/