Wine Fans Take Heart: Smells Differ in Nose, Mouth

New research shows that the brain perceives an odor differently if it arrives through the nose rather than through the mouth. The finding validates techniques that wine tasters have been using for centuries to assess a vintage.

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Scientists who study the brain have confirmed something that wine connoisseurs have know all along. The brain perceives an odor differently depending on whether the odor arrives through the nose or the mouth. NPR's Jon Hamilton reports.

JON HAMILTON reporting:

It's called wine tasting, but what people like Michael Franz actually do is more like wine smelling.

(Soundbite of glass object being tapped)

HAMILTON: Franz is the editor of winereviewonline.com. He also writes a wine column for The Washington Post. We're standing in his kitchen, where he's ready to sample a half dozen Chardonnays from Oregon. He lifts the first glass to his nose.

So what are you smelling?

Mr. MICHAEL FRANZ (Wine Connoisseur): In the case of this particular wine, a fairly ripe, almost baked apple aromas.

HAMILTON: Next, Franz takes a sip but he doesn't swallow the wine.

(Soundbite of slurping)

HAMILTON: A little later he explains what that slurping is all about.

Mr. FRANZ: I actually am trying to draw air over the wine to volatilize the compounds that are in it and actually be able to smell it as I'm tasting it.

HAMILTON: Franz says wine tasters get different information from this method of smelling the wine, and scientists say that's possible because odors can travel up into the nose through the back of the mouth. But they weren't sure if the brain treats odors that arrive through the mouth the same as those that come through the nose. So scientists at Yale University and the University of Dresden decided to do an experiment. Dana Small is at Yale.

Ms. DANA SMALL (Yale University): The question we were interested in is: Are these two separate systems, or is this just two routes to get to the same neural system?

HAMILTON: To find out, the team studied 11 people using an MRI scanner that measures brain activity. The scientists used plastic tubes to deliver odors to each volunteer. One tube released odors near the tip of the nose to simulate sniffing. The other released odors near the back of the mouth to simulate eating or drinking or wine tasting. The route didn't make much of a difference when people smelled lavender or two chemical odors. But Small says the brain images changed when people smelled a favorite candy.

Ms. SMALL: The effect was huge for chocolate compared to these other odors, and that's interesting because, of course, we don't go around putting non-food odors into our mouth. We don't sample perfume with our tongue.

HAMILTON: Small says it appears that once our brain learns that something is a food odor, it can tell whether the odor is coming from outside the body or inside the mouth. Jay Gottfried of Northwestern University says this ability to figure out where an odor is coming from may help explain how we learn to enjoy foods that can smell pretty gross.

Mr. JAY GOTTFRIED (Northwestern University): For example, the classic case of a Limburger cheese, which smells so pungent and, you know, like sweaty socks when you stick your nose into it. But if you're willing to get past that, take a risk and put the cheese into your mouth, it takes on a much more mellow and nutty flavor, something that you wouldn't expect from just sniffing it.

HAMILTON: Gottfried says Small's work suggests that our sense of smell is pretty sophisticated, but it's nowhere as sensitive as your average animal's. Gottfried says it's no accident that people use dogs and pigs to sniff out a truffle six inches underground.

Mr. GOTTFRIED: There is the rare truffle hunter who goes without pig or dog and can smell it out. Often they're relying on other cues such as the appearance of flies around the base of an oak tree.

HAMILTON: Gottfried says wine tasters are also using more than their sense of smell to make a find. Michael Franz, the wine critic, agrees. He says he never gives a final verdict on a wine until he's considered more than its bouquet. He gives one Chardonnay another try.

(Soundbite of slurping)

Mr. FRANZ: Interestingly, the wine shows much more depth and dimension on my palate than it did when I was just smelling it. Beautiful rich flavors, very nicely balanced, finish is long and symmetrical, very nice example of this type.

HAMILTON: You can read the latest research on how the brain perceives food odors and that glass of Chardonnay in the journal Neuron. Jon Hamilton, NPR News.

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