Bite down on a perfectly ripe strawberry and the pure sweetness of the juice hits you first. Then comes something far more complex: Your tongue feels rough seeds punctuating soft fruit, and a hint of sour breaks through the sweetness. If you had to name it, the word “tang” may drift forward.
This isn’t exactly a taste, but some intangible quality that makes a strawberry go so well with whipped cream and hold its own as a bastion of summer. The strawberry-ness of a strawberry is hard to put into words, but somehow, even with your eyes closed, you know it instantly apart from a raspberry or a blueberry based on a swirl of perceptions that together form the complex and poignant experience of flavor. That this experience happens immediately is a finely tuned dance of the senses that would be impossible without the brain as its choreographer.
What is flavor?
The only thing scientists who study flavor agree on is what it is not. It’s not a standalone sense like taste. But a unifying definition of what flavor is continues to escape those who study it. The purists among them think this multisensory experience arises simply from the brain combining the sensations of smell and taste. The progressives of the group regard flavor as bringing together smell, taste, and mouthfeel—the physical quality of food as the tongue touches it. And the scientific experimentalists see flavor as something even bigger.
“I think flavor involves also vision and hearing,” says Qian Janice Wang, assistant professor of food science at Denmark’s Aarhus University. But, she concedes, “I’m sure that everyone you talk to might give you a different definition.”
Dana Small, a neuroscientist at Yale University who studies how the brain mediates our behavior toward food, is open to the idea that the sound of eating a food—the auditory experience of a crunch, for example, not just the textural sensation of it—may directly play into flavor perception. But she rejects including the role of vision as integral to flavor. Seeing a steak dyed green would surely change your behavior toward eating it, but that’s separate from the sensory experience that happens once you do eat the food. “I think it’s very interesting that we do not have an agreed-upon definition,” says Small.
Then there’s Gordon Shepherd’s view on the debate. He made a monumental discovery about smell in the early 2000s that changed neuroscience and paved the way for a hybrid discipline called neurogastronomy. “Flavor is created by the brain,” he says simply and with awe still.
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Although it’s hard to imagine, there is no flavor intrinsic to food, just as objects do not contain color but rather reflect wavelengths of light that we interpret as yellow, red, blue, and so on. It’s our big, complex, interconnected brain that makes flavor—this delightful, disgusting, memorable, and emotional experience—and links it to food. Without the brain, a peak season strawberry would be nothing special at all.
Taste vs flavor
Taste and flavor aren’t the same thing. Specialized receptors on the tongue give rise to the five sensations that comprise taste: salty, sour, bitter, sweet, and umami. Any experience of food more complex than that falls into the realm of flavor. This is crucial, yet the way most people talk about what they eat or drink lags behind the physiological reality.
“When people say something tastes good, they usually mean its flavor is good or its sensory properties are good,” says Robin Dando, associate professor of food science at Cornell University, where he studies how humans evaluate food using their senses. But a few minutes later, even he—an expert—starts slipping up in the middle of a conversation about defining these very terms; it’s a hard colloquialism to break. “I’m saying taste, and I’m dropping back into this language that I tell my students not to use,” he says laughing.
Beyond confusing taste and flavor, language hides another mix-up, this time between taste and smell. The bulk of flavor actually comes from hundreds of receptors in the layer of skin that lines the nose—the olfactory epithelium—not the tongue. When someone says something tastes aromatic, what they really mean is it smells that way, yet the sensation seems to be coming from the mouth, says Jessleen Kanwal, a postdoctoral fellow at Caltech. It’s perplexing, to say the least, but here’s how this mix-up begins.
Chewing a tasty morsel with your teeth releases volatile compounds, chemical signatures of food that evaporate up into the back of the nasal cavity where nose and mouth join. As you eat, you exhale out through your nose, which pulls these compounds along a current of air from the mouth directly onto receptors in the nose’s olfactory epithelium; such receptors can detect immediately. It may seem odd to look to a minuscule insect for clues about the human brain, but the fruit fly’s olfactory system is quite similar to that of mammals. “That really changes the way we think about how the brain is organized,” says Kanwal.
When people who lose their ability to perceive flavor describe the experience of eating, they often compare it to living in black and white. Even with imprecise language that confuses taste and flavor, and taste and smell, when we lose the ability to smell, there is still an emotional understanding that, with only taste, food becomes flat and uninviting. But one reason this is rarely articulated may be because the brain is tricking us into perceiving retronasal smell, and thus flavor, as coming entirely from the mouth.
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The importance of illusions
How you cognitively perceive the world is actually a pretty poor representation of the way the world is in reality. The kind of gimmicky optical illusions featured in children’s science books—such as staring at a static picture of a circular checkerboard and perceiving the rows as spinning in alternate directions—are the best known of these perceptual mistellings, but we all encounter them throughout the day in other sensory systems and in such highly assimilated ways that we’re likely unaware they’re even happening.
Watching television activates such a spell. You experience the sound of the actors speaking as coming directly from their mouths, but if you stop to think about what you know of how a television works, that doesn’t make sense. The sound, of course, is coming out of the television speakers, separate from the moving image of a person talking. Because the sound and image are coming from roughly the same place in space and time, your brain makes the world a kinder, simpler place and you experience the two sensory inputs as being one event.
This experience typifies where sensation ends and perception begins, says Small. Only a technical difficulty might ruin the illusion—anyone with a streaming service and a bad internet connection knows the vexation of hearing spoken words out of sync with a moving mouth.
The perception that flavor is born in the mouth is another such daily illusion, a gastronomical trick the brain plays that belies how your body actually works. When you’re chewing that ripe strawberry, receptors on the tongue relay chemical information about taste to the brain separately from receptors located in the nose, which are also relaying chemical information to the brain, but about smells. The brain receives both at about the same time, and from almost the same place on the body. The brain’s somatomotor mouth area simplifies this process and tethers both sensations to the mouth.
This experience is called the oral capture illusion. In doing this, the brain finely differentiates between information coming from the receptors at the back of the nose, those that sense chewing-related smells, and receptors at the front of the nose, those that sense smells in the environment. If the brain were to mix up the information from these two sets of receptors—which are physically only about one inch apart in your body—you’d perhaps experience the unpleasant smell of mothballs as though it were coming from your mouth.
“There are a lot of illusions that make up perception, and in this case the trickery makes a lot of sense,” says Small. “It’s basically imperfect physiology trying to do a better job at capturing reality.” The reality is that as you eat, the strawberry you feel in your mouth—and nowhere else on your body—does singularly contain all of these chemical compounds, even though the receptors for sensing them are in different places.
“Imagine the evolution that has to happen in order to create oral capture illusions,” says Small. “It’s a lot of physiological gymnastics to go through, so it must have an important purpose.”
The purpose, as she understands from both scientific and personal experience, is to help you differentiate nutrients from toxins in a highly sophisticated and nuanced way. “The classic example is conditioned taste aversion, which is actually conditioned flavor aversion,” says Small.
When she was 19 years old—within the legal drinking age in her native Canada— Small celebrated the Swiftsure Regatta, a series of weekend yacht races that course through the Strait of Juan de Fuca, the geographical border between her home on Vancouver Island and Washington State in the United States. At the regatta parties, Small, new to alcohol at the time, had an all too relatable run-in with coconut-flavored rum cloaked beneath syrupy soda. In the end, she got sick.
“To this day, I will not drink a Malibu and Seven-Up,” says Small. “However, in the ensuing 30 years, I didn’t develop an aversion to sweet things, I formed an aversion to the exact thing that made me sick.”
Without flavor, and only taste, this learned reaction could have pushed her to eliminate unrelated sweet foods from her diet that provide sources of nutrients and energy needed for survival, such as bananas or milk. “That’s the value of flavor, which is hugely important in terms of adaptation.”
