Wine is such a mysterious beverage. We 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 is 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 if you slice a grape open. This is why wine grapes are generally small and round. Table grapes seem to get larger, longer and more seedless every year (and in my opinion, a little more tasteless.) Wine grapes, unattended in rich soil, can also become quite large. But winemakers want smaller grapes, which have a higher skin-to-juice ratio, resulting in wines with color, flavor and tannin.
Some grapes, like syrah, nebbiolo and cabernet sauvignon have naturally higher levels of tannin than other grapes. Winemaking styles also preserve or delete some of the tannins in wine.
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 wine tasters claim that a completely dry wine tastes “sweet” to them. What they are tasting, however, is a dry, fruity wine with very little of the drying astringency contributed by young tannins.
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, 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.
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.
This is also why it’s difficult to properly taste white wines after drinking red wines. The drying effect of fresh tannins results in what winemakers call “palate fatigue”.
It’s also possible, if you are confused about whether you like wines that are slightly sweet 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.