Tannins in Wine

Wine is such a mysterious beverage. Wine geeks will sniff it, quaff it, swizzle it, and then come up with all these wild descriptors: cassis, meadow, leather, mushroom. Where do all these elusive aromas and flavors come from? Partly from the grape, partly from aging in oak, (partly from our imaginations), and partly from tannin.

Tannins are a group of chemicals that occur in the bark of many trees, cinnamon as an example, and in fruits, including grapes. Tannins are also present in black tea, and cause the astringent, drying effect that you experience after several cups of strong tea. You'll also notice a dry, sandpapery effect in your mouth after eating a whole bunch of table grapes. The tannins in grapes are a woody substance in the skin and seeds.

The pulp of a grape is mostly juice, as you can see when you slice a grape open, and the pulp is generally white or pale pink in color. This is why wine grapes are generally small and round. Most of a grape's flavor, and all of the pigment, comes from the skin and the fibrous layer directly under the skin.

White wines are made without much contact between the juice and skins. Without the blue pigments and flavors of red grapes, the skins of white grapes are simply bitter, and are discarded early in the winemaking process. Woody flavors in white wines are generally contributed by oak. Red wines, however, are allowed to ferment for up to ten days with their skins and seeds, and sometimes stems as well. In fact, as the skins and seeds float to the top, winemakers and cellarmen make an effort to punch them back down into the wine several times a day; much the same as stirring a slow-cooking pasta sauce.

Table grapes seem to get larger, longer, and more seedless every year. Wine grapes, unattended in rich soil, can also become quite large. I have seen bunches of zinfandel grapes as long as my forearm and as heavy as a small salmon. But this is exactly what winemakers do not want. Smaller grapes have a higher skin-to-juice ratio, resulting in wines with better color, flavor and tannin.

Tannins are derived from flavonoids, a condensation of catechin and proanthocyanidins. Catechin, a natural compound used in tanning hides, is also making press in health reports these days as one of nature's compounds responsible for maintaining a healthy heart. Proanthocyanidins simply mean pro (from), cyan (blue), antho (plants); meaning a complex of substances derived from blue fruits like grapes and plums.

Tannins, which are insignificant in white wines, quite strong in young reds, and softened in older red wines, have a drying effect on the palate. Some grapes, like Syrah, Nebbiolo and Cabernet Sauvignon have naturally higher levels of tannin than other grapes. Pinot Noir and Merlot have gentler tannins. Winemaking styles also preserve or delete some of the tannins in wine.

Wine tasters sometimes claim that a completely dry wine tastes "sweet" to them. What they are tasting, however, may actually be a dry, fruity wine, yet with very little of the drying astringency contributed by young tannins.

Tannins play an important role in the aging of wine, particularly red wine, and need careful mastery during wine-making as they can taste bitter and astringent if the fruit is squeezed too hard in the press, or if the skins are left in the juice too long—sort of like making your tea too strong. Handling the skins and seeds during winemaking is one of the most critical steps in optimizing the quality and character of red wine.

Tannins in wine come from both the grapes, and the wood in which it was aged. However, the tannins in oak differ in significant ways from grape tannins. And since wine barrels hold fifty-five gallons or more of wine, the ratio of wood to wine is less and the effect gentler.

Over time, as wines mature in the barrel, and particularly as they age in the bottle, tannins soften. The tannin molecules agglomerate and polymerize, chaining together to form larger, more complex substances, so that eventually those molecules above a certain size precipitate as sediment and no longer have any bitter or astringent effect on the palate.

Medium-sized polymerized tannins interact with the proteins of taste buds sensitive to bitterness, while larger ones function as tanning agents and a natural preservative. This is why well-made red wines can age for years, while white wines should generally be drunk young.

This is also why it's difficult to properly taste white wines after drinking red wines. The drying effect of tannin results in what we call "palate fatigue." I generally suggest to wine tasters that instead of tasting the entire gamut of white and red wines at several wineries, that they set up a wine "quest" for the weekend, and only taste whites or reds, but not both.

It's also possible, if you are confused about whether you like wines that are sweetish or completely dry, that you prefer a certain level of tannin and oak. There are many levels of tannin structure in wines, in addition to the varying elusive flavors of the grapes. The next time you go wine tasting or buy a new brand of wine, take your time and study its aroma, its flavors, and that leathery, woody, seedy component called tannin.

Comments

[Mike Duffy]

Wow! Mary, another tour de force. I always enjoy the flow of your words, but this was above the norm. Who would think it possible to wax lyrical about tannins? Thanks for another great post.

[Mary Baker]

Thanks, Mike! I don't know about 'lyrical,' but I do enjoy writing about wine . . . it's always a boost to know that someone is actually reading this stuff! ;)