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environment general science genetics health and medicine space technology January 20, 2003 
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Making Sense of Science

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April 03, 2001

Also on ScienCentral News

The Nose Knows - The senses of taste and smell seem to work together in a way researchers had not known before. (12/14/00)

What causes cork taint in wine? - (4/03/00)

Is there a physiological basis for why people have different taste preferences? - (12/19/00)

Elsewhere on the web

A. C. Noble’s Sensory Science Homepage

UC Davis Viticulture and Enology Homewinemaking - Download information about making wine at home.

How to taste and serve wine and why - Information about buying, serving, tasting.

Wine Lovers’ "Wine Questionary"


Scientists can classify all kinds of things, but can they classify smell? And if so, how precisely?

One California researcher has stuck her nose into the issue of the smell and taste of wine. As the ScienCentral News video report at the right shows, she’s found some unique ways of classifying smell.

Wine connoisseurs say that many wines should ‘breathe’ before you drink them. Why is that?

Ann C. Noble, PhD., Professor of Viticulture and Enology in the College of Agricultural & Environmental Sciences at the University of California at Davis, replies:

Well, let’s correct it. Many wine experts say that, and many other experts disagree with them. Each wine is different, and I think there are four scenarios. One, You could blow off a defect. If it’s a younger wine and it has an off-odor, very often there’s a very little bit of the volatile sulfur compound defect hydrogen sulfide, which is like rotten eggs. And if you open it up, that goes away very, very quickly. So that’s a good reason to open something to breathe.

Two, on the other hand, you could lose some really good things because the wine is so old. In older wine, if you open it up early you may lose a lot of the things that it had going for it—the aromas. And that happens—not always, just sometimes.

The third one is nothing happens.

And the fourth one is, it is one of those younger reds that actually does seem to have a development occur, and by that I mean the aroma seems to change by having, you know, being poured, fifteen minutes ahead of time. Sometimes if you open it up and let it breathe, just sometimes, it does actually seem to help the aroma develop. "Seems to" is the operative phrase here. It’s only for certain red wines in which that happens. And just opening the bottle isn’t going to do it. You’ve got to open the bottle and decant it to get enough air in there.

Letting it breathe in the bottle is not going to do very much for it because there’s very little exchange with the environment, whereas if you pour into a glass or a decanter, you are aerating it, meaning that you’re getting oxygen in there, and you’re splashing it, so some of these volatile compounds will go away more quickly. You’re going to have more of an effect than if you just pull the cork and let it sit there.

So in some cases it makes a very positive difference, and in other cases, actually, with older wines, it can make a negative difference. However those four scenarios can’t be predicted ahead of time, and except for the volatiles blowing off, I can’t give you a chemical reason.

Wine Wheel
The wine wheel
For a larger image click here.

Now, about the volatiles blowing off: How this happens is, if you have these very volatile defects, that means they are compounds that are probably potent—that is, you can smell them at very low concentrations—and also they happen to have what we call a "very low boiling point." That means they turn from liquid into gas, and therefore, they’re in the air above the wine and they will go away very quickly. And so when that happens, you lose that smell very quickly. It’s almost exclusively the aroma that is affected. The taste should be unaffected. There’s one or two people that are on a bandwagon, that if you open up a red wine and shake it or something like that, that you can affect its perception of astringency, but I can’t believe it, and in my research, I don’t think it’s possible.

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