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The Nose Knows
December 14, 2000
image: Butterball

If you’re like most people, you’re probably looking forward to the tastes of special foods that this time of year brings. But how much of that eggnog or roast turkey flavor actually comes from taste? It may not be as much as we think.

Researchers have recently shown that the senses of taste and smell seem to be intermingled, and that how familiar we are with the flavor of certain foods may have a lot to do with how sensitive we are to their taste.

A budding experiment

Pam Dalton, a research scientist at the Monell Chemical Senses Center in Philadelphia, PA, wanted to find out how much our noses contribute to the flavor of food. Dalton conducted a study to test how much smell and taste are combined. She asked subjects to sample odors and flavors together at much lower concentrations than would normally be detectable by smelling or tasting alone.

"What we learned in this experiment is that things that you cannot smell by themselves or things you can’t taste by themselves, when they’re experienced together, all of a sudden become very detectable and recognizable as a flavor sensation," she says. "So we learned that the brain is capable of putting together the sensations from the taste and the smell system even when their concentrations are below what the brain could be able to interpret by themselves."

Brain scans reveal activity that occurs when someone is smelling and tasting.
image: Montreal Neurological Institute

The experiment started by finding the subjects’ odor threshold to a cherry smell and, separately, their taste threshold for saccharin. Once that was established, subjects were asked to sample both substances combined—smelling and tasting simultaneously—but at half the concentration. "If a person could then distinguish them, then we know that the brain was somehow putting together this information from the taste and the smell system and adding it into a perception that an individual could recognize as a flavor," Dalton says.

But the results also showed something else. Familiarity with a particular flavor combination seems to have a lot to do with how sensitive we are to it. Dalton found, for example, that while subjects could recognize the pairing of a cherry smell and sweet taste at very low concentrations, they were unable to do so with the pairing of a cherry smell and savory taste, which is an unfamiliar combination to most Americans.

"From this result we believe that we have evidence that learning or familiarity is very important in helping the brain to add together these flavor combinations," says Dalton. This may help explain the attraction of eating traditional foods during the holiday season. Because people are more used to certain flavors, Dalton says, they are more sensitive to them and therefore may enjoy them more.

The aroma of taste

When we taste something, there are five different types of receptors that give us information about its flavor: sweet, salty, sour, bitter, and savory. But we can smell thousands of different chemicals, Dalton explains. So smell has a lot more to do with how food tastes than one might think. In fact, studies have shown that as much as 75 percent of the flavor we perceive from food is actually attributable to our sense of smell.

Tasty, smelly facts

•Dogs have 1 million smell cells per nostril and their smell cells are 100 times larger than humans.

•If your nose is at its best, you can tell the difference between 4000-10,000 smells.

•We have almost 10,000 taste buds inside our mouths, even on the roofs of our mouths.

•Insects have the most highly developed sense of taste. They have taste organs on their feet, antennae, and mouthparts.

•In general, girls have more tastebuds than boys.

courtesy Think Quest Junior

"People who have lost their sense of smell for various reasons often stop enjoying [any] food whatsoever, and can lose enormous amounts of weight," she says. "The contribution of our olfactory system to food flavor is so pronounced that when people don’t have the ability to smell anymore, they really don’t enjoy eating."

What would it be like to live without a sense of smell? According to Dalton, it would be a fairly one-dimensional experience. "Fruits would taste sweet, vegetable would taste bitter, but we wouldn’t have the dimension to allow us to tell a raspberry from a strawberry, or spinach from broccoli," she says. "We would just have a taste sensation. Smell allows us to add on the other dimension that allows us to discriminate many different—hundreds or thousands of different—types of food."

The contribution of our olfactory system also accounts for why food doesn’t taste very good when you have a cold. "Most people think that their taste system is affected when they have a cold, but in fact their taste system is functioning normally," says Dalton. "It’s their ability to smell the food that is not working very well."

So if this holiday season finds you with a cold and you can’t tell a fruit cake from a panettone, Dalton suggests sticking with foods you’re familiar with. Even if you can’t smell them very well, your brain should be able to fill in the sensory gaps and make them taste better.

Elsewhere on the web

Aging and the Sense of Smell

The Mystery of Smell

New evidence connects nausea to sense of smell

Your sense of smell

Your sense of taste

Digiscents (company attempting to bring smells through your computer)

by Jill Max

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