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Aeration -- friend and enemy of wine
Daniel Sogg
Posted: November 15, 2003

Decanting is one of the more traditional elements of formal wine service -- and one of the most controversial. Opinions differ widely as to which wines reward decanting and on how long before serving to decant a wine. The stakes can be high. Bottles poured too far in advance of drinking may crack up, or fade like a wilting flower. But decant too late, or not at all, and a wine's best may be unveiled only in the final teasing sips.

Decanting has an aesthetic upside -- nearly any wine looks more enticing in stylish crystal. It is also the most practical way to eliminate sediment in older wines. But fundamentally, the question of when (or if) decanting is justified depends on how the wine reacts to aeration. Age and bottle condition, varietal composition and production techniques are important variables.

"It doesn't necessarily matter if it's Merlot, Cabernet Franc or Cabernet Sauvignon," says Bob Levy, winemaker at Harlan Estate and Bond in Napa Valley. "If the wine has good ripeness, extraction and a fleshy midpalate, then I tend to think that aeration can benefit the suppleness of the tannins and the overall expressiveness of the fruit."

From a chemical standpoint, decanting exposes a wine to air, triggering oxidation and evaporation. Wine is extremely complex, containing literally hundreds of compounds, but the fruit character that provides much of a wine's allure comes from a relatively small portion of them. Unfortunately, these crucial compounds oxidize easily. An oxidized wine will be stale and flat, devoid of richness. A wine's response to aeration depends upon its fruit concentration, as well as factors (such as pH and temperature) that mitigate oxidation.

Other compounds in wine can inhibit the expression of fruit character. Sulfites, for example, are added during the production process to prevent oxidation and inhibit microbial activity, but in excess they can impart a burnt matchstick character. Sulfides, a different class of compounds, can form naturally during winemaking and in the bottle, imparting undesirable traits such as rotten egg and onion skin aromas. Ideally, decanting allows undesirable compounds to evaporate faster than the fruit oxidizes.

The common wisdom is that young, brawny reds, such as Syrahs, Bordeaux and Barolos, benefit most from air exposure. Decanting can create a sort of sweet spot, a window during which these wines can display added polish, intensity and fragrance.

Many vintners and consumers assume that decanting improves reds by softening tannins. Strictly speaking, that's a fallacy.

It's true that controlled aeration during vinification affects tannin structure; one primary reason for barrel aging tannic reds is that air seeps through the pores of the wood into the wine. The oxygen is thought to catalyze a chemical reaction that polymerizes tannins -- bonds shorter molecules into longer chains -- to give a smoother mouthfeel. But tannin polymerization requires days and weeks -- not hours -- to take place, according to Andrew Waterhouse, professor of enology at the University of California, Davis, the state's leading wine research institution.

"Very few chemical reactions occur quickly in wine," says Waterhouse. But he does endorse decanting for other reasons. "You'll get a lot of evaporation changes that radically alter perception. If you get those sulfur-based molecules to evaporate, the wine tastes quite different without them."

Essentially, it's about reference frames. Decanting doesn't alter tannins. But as undesirable compounds dissipate, fruit seems to intensify, which gives an impression of softened structure. It's often the case in wine that the presence of one compound influences the way another is perceived. For example, a late-harvest wine (loaded with sugar) may still taste relatively dry if it has significant levels of acidity to balance the sweetness.

In effect, decanting is addition by subtraction. So it's understandable that white wines can benefit every bit as much as reds. Johannes Selbach, owner of Selbach-Oster in the Mosel region of Germany, noticed that his higher-end Rieslings consistently improve with aeration. "We learned by experience. There was nothing scientific about it. We found that the wines taste better the next day," he says. "The higher the density, the higher the concentration, the more they benefit."

Selbach sees that as a consequence of his winemaking techniques. His Riesling gets little exposure to air during production, so it can go into bottle with a variety of fermentation aromas, such as yeastiness, as well as dissolved carbon dioxide. Aeration allows the gas and fermentation character to dissipate, which lets the wine's fruit and minerality take center stage. Of course, much depends on personal preference.

Napa vintner John Kongsgaard, winemaker for Arietta Wines and his own, eponymous label, finds that his young reds made with Syrah and the Bordeaux varieties benefit from decanting. "They smooth out in the mouth and become more focused in the aroma," he says.

But prolonged aeration can adversely affect oaky, tannic young reds. That was the case in an experiment we performed at the Wine Spectator office in San Francisco. Four bottles of an outstanding 1999 Napa Valley Cabernet Sauvignon were given varying amounts of aeration, then tasted blind. Three bottles were decanted, at 24 hours, six hours and 90 minutes, respectively, prior to drinking. A fourth bottle was uncorked and tasted immediately.

Associate editor Tim Fish and I agreed that the wine opened for 24 hours was the least appealing. The fruit wasn't as bright and the tannins seemed relatively harsh. Fish's favorite was the 90-minute bottle, while I preferred the wine that had just been opened.

In general, the tannins seemed to grow greener and less supple with aeration, while the fruit lost vibrancy. We also observed that the cedar and vanilla notes from new oak barrels grew progressively more dominant. Although oak tends to integrate with bottle age, aeration magnifies it in young wines as oxidation reduces fruit character. Our advice is to be conservative when decanting young red wines, tasting frequently so as not to miss their sweet spot.

For older reds with sediment, decanting is advisable. Although sediment, which is comprised mostly of color and tannin molecules precipitated out of the wine, forms naturally during maturation and poses no health dangers, it should be removed before serving. Otherwise it clouds appearance and can impart bitter flavors and a gritty texture.

It's difficult to predict how much sediment an older wine will contain. While it's sometimes possible to inspect a wine with a strong light, it's wise to assume that reds start accumulating sediment with five to 10 years in bottle. Some wine types, such as Vintage Port, generate significantly more sediment than others, such as red Burgundy. White wines rarely develop sediment.

Proper decanting requires forethought and a steady hand. Ideally, the wine should stand upright for three or four days to allow any sediment to settle. Some particles can be fine as dust and need several days to collect on the bottom of the bottle. Decanting older wines is a simple process, though exacting. After the bottle is gently uncorked, the capsule should be removed and the neck wiped clean. A bright light, such as a flashlight beam, should be positioned under the neck of the bottle. Then, the wine should be poured slowly and steadily into the decanter, until sediment reaches the neck. The remaining ounce or two of wine, with sediment, should be discarded.

Wines should be served sediment free. But mature bottles sometimes lack the fruit to withstand aeration, so Kongsgaard prefers a cautious approach. "Once they really develop bottle bouquet, I think it's very possible you'll miss something in that first hour," he says.

Generally speaking, discretion is the better part of valor for bottles 15 or more years old. So gauge a wine's condition before decanting. Pour a small taste (carefully, though, so that the sediment isn't disturbed). If the wine shows well, decant just before service. But if it seems closed and unexpressive, moderate aeration in a decanter might bring about a memorable transformation.

Vintners employ methods of controlled air-exposure during the various stages of production. And this is a technique that consumers, too, can employ, helping shape their wines according to their personal tastes. Only experimentation reveals when decanting will benefit your wines, or when it might harm them.

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