Swirl the Wine

Many wine lovers uncork a bottle of their favorite red and set it aside for a few minutes to let it breathe. But that won't happen through a bottle's narrow neck, according to a light-hearted report presented today at the American Lung Association/American Thoracic Society International Conference in Chicago. The study supports recommendations from wine experts that people decant red wine before drinking it.

When a friend suggested letting a bottle of wine breathe before dinner, Nirmal Chran was dubious. "I told him we could let the wine sit here forever and it still won't breathe," recalls Chran, a researcher at the Pulmonary Research Laboratory of the Veterans Administration Medical Center in Boise, Idaho. To back up his preprandial challenge, Chran stuck a needle through the corks of five unopened bottles of Cabernet Sauvignon and measured the partial pressure of oxygen and carbon dioxide at the top of the bottle and the bottom.

Carbon dioxide levels in the wine were much higher than air, while oxygen levels were 5 times lower. (That's normal, because the yeast that ferments the grapes eats oxygen and burps carbon dioxide.) Chran then popped the corks and measured the gas pressures 2, 4, 6, and 24 hours later. The pressures varied little over that time, either at the bottle's top or bottom, he says. However, after pouring himself a glass and swirling it for 2 minutes, Chran found that the gases in the wine had come into equilibrium with those in the air. And according to an ad-hoc group of 10 or so off-duty VA hospital employees, the wine flavor improved after swirling.

To find out if increased oxygen levels are responsible for better flavor, Chran bubbled oxygen through a corked bottle of wine. When oxygen levels reached those of air, his panel members--after clearing their palates, of course--found that the wine tasted better than that left to breathe in the bottle. No one really knows why flavor improves after breathing, says Andy Waterhouse, a wine chemist at the University of California, Davis. He thinks that malodorous molecules may evaporate from an uncorked bottle, but he doesn't rule out a role for oxygen.

Posted in Chemistry