The tannins in the stems, seeds, and skins are largely responsible for the aging capability of red wines.Tannins are an astringent compound found in plants that are responsible for the gritty texture in red wines. They have no flavor or aroma but can be experienced as dryness.

The word tannin stems from the use of this compound to “tan” leather. Which is why your tongue feels a little like leather when drinking a high tannin wine without food.

Wikipedia defines tannins as “an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids”.

That is certainly a mouthfeel but the key points are that it is bitter and that it binds with proteins. Both of these characteristics is what leads to that dry taste red wines are known for.

Where do Tannins Come From?

Wines pick up tannins from the stems, seeds, and skins of winemaking grapes. White wines, as you know, do not undergo a long maceration (aging on the skins). Because of this they have little in the way of tannins and they don’t pick up the coloring of the skins.

Red wine must on the other hand is fermented an let to sit with the skins and seeds for some time in order to extract the maximum amount of flavor, aroma, and color. However, they pick up a lot of tannins along the way.

Oak is another source of tannins. Red wines often being aged in oak can pick up still more tannins. You can see that the control of tannins is a concern when making red wines.

Tannins may also be purchased in a powdered form and added to your wine if you find it lacking. Often this is done with wine kits which are low in tannins so that they become drinkable sooner (read this).

Tannins and Protein

As I mentioned earlier the fact that tannins interact with and precipitate proteins is a key point to understanding tannins. When tannins come into contact with proteins they bind together and sink to the bottom of whatever container they are in.

This removes both the protein and the tannin from the wine. An excess of protein in wine can cause haziness. However, due to the presence of tannins during fermentation most of the protein is precipitate out.

The biggest effect of this interaction comes when drinking red wines. Take a sip of red wine without any food and you’ll notice that your tongue feels dry and unprotected.

This happens because the tannins in the wine bind with proteins in your saliva. When this happens your tongue is left “exposed” and feeling like you just licked a 2×4.

It is this precipitating action that makes red wines go so well with high protein foods like steak and sharp cheeses. The tannins bind with the excess protein in your mouth and makes the wine much easier on your mouth. Not to mention how nicely the flavors of red wine and heavy proteins go together.

Tannins and Time

Have you ever wondered why red wines are aged for so long while whites normally aren’t? Well, a good part of the reason is the level of tannins in the wine.

Something really special happens to tannins when aged for long periods of time. They bind together to form longer molecules.

The longer the tannin molecule gets the smoother your wine will taste. Young, short tannins can be quite harsh. Wines with high tannins need more time in the bottle to mature and develop into a palatable wine.

This explains why red wines age to perfection. They are left on the skins for a long time extracting the maximum amount of flavor, aroma, and color compounds. With that comes additional tannins and the ability to get better with age.

Over time the tannins smooth out and you’re left with a sophisticated, flavorful, aromatic, and beautiful red wine. It takes time though and you do have to be prepared to wait it out.

Given enough time tannin molecules can get so long and heavy that they fall to the bottom of the bottle. If you’ve ever opened an older bottle of red wine you may have noticed a bit of red debris in the bottom of the bottle. Those are all the tannins that have dropped out.

In Summary

Here are the main take aways regarding tannins:

1. You can not taste or smell tannins, they can only be perceived in mouthfeel.
2. Tannins come from the stems, seeds, and skins of the grape as well as oak chips or barrels.
3. Tannins bind with proteins to give you that dry sensation.
4. Over time the tannins bind together and make for a silky smooth wine.

Photograph of red grapes by: Jim Bahn