Flavor

by Bob Holmes

  That makes researchers’ lack of interest rather surprising—especially since, if you think about it in the right way, we all know that multiple senses must contribute to flavor. Imagine, for example, the wonderful taste of ripe strawberries slathered with vanilla-laced whipped cream. Easy, right? But now remember that all you really taste is sweet, plus maybe a little sour from the berries. All the rest is smell, experienced in the nose—yet it seems for all the world to be a taste, experienced in the mouth. Even worse, we often say the berries smell sweet, even though sweet is the one part of the flavor experience that we’re not actually smelling. We’ve grown so used to combining smell and taste into a single flavor, though, that we commonly confuse them. “Maybe it’s so common, in fact, that people never think about why strawberries smell sweet,” says Spence. This kind of sensory magic also explains how the mere scent of peppers or rosemary lent their flavor to the plain goat cheese in Hobkinson’s dinner—as long as the guests’ dominating visual sense wasn’t present to spoil the illusion.

  Scientists, of course, are rarely content with this sort of vague hand waving, so Spence—along with several researchers in other labs—brought this sensory cross-wiring into the lab for dissection. More than a decade ago, for example, Richard Stevenson at the University of Sydney, Australia, had volunteers rate the sweetness of pure sucrose, an odorless sugar, both alone and in the presence of a caramel odor, which the researchers verified had no sweet taste on its own. Sure enough, the sugar tasted sweeter when people also smelled the caramel.

  A whole host of similar studies show that the effect is widespread: Odors such as vanilla and strawberry also make sugar taste sweeter. Strawberry aroma enhances the sweetness of whipped cream, while peanut butter aroma doesn’t. Chewing gum “tastes” less minty—really a smell and a mouthfeel, not a taste—as it loses its sweetness, and the mintiness returns when the researchers slip in a second dose of sugar.

  Sometimes, these experiments point to another noteworthy fact: Smells and tastes often go together differently for different cultures. For example, caramel odor doesn’t enhance sweet tastes for many Asian people, who are likely more used to encountering caramel in savory dishes instead of the sweets that Westerners are used to. The same thing happens with benzaldehyde, the main component of almond aroma. It enhances sweet tastes in Westerners, who usually encounter almond in pastries. But for Japanese, benzaldehyde enhances umami taste, because almond is a common ingredient in savory pickles.

  In fact, researchers have found that they can mess with people’s smell/taste perceptions almost at will. Several years ago, John Prescott of the University of Otago, New Zealand, and his colleagues got their hands on some obscure odors that people would have no prior associations with. Then they presented those odors to volunteers together with either a sweet or a sour taste. After familiarizing the volunteers with the combination a few times, they tested the smells and tastes separately. Sure enough, sweet tastes seemed sweeter—and sour ones sourer—when the volunteers smelled whichever odor they had learned to associate with that taste. In short, we learn how to put smells and tastes together to create flavor.

  It doesn’t take a great leap of faith to accept that smell plays a big part in our perception of flavor. As Spence likes to point out, that notion has even penetrated that bastion of bureaucratic bean counting known as the International Organization for Standardization. As its name suggests, this is the agency that sets definitions and industrial standards for everything from telephone dialing codes (ISO 3166) to energy-efficient buildings (ISO 16818). If you like that sort of thing, and have the patience to wade through volume after volume of technical specifications, you’ll eventually come across ISO 5492, which defines flavor as “a complex combination of the olfactory, gustatory and trigeminal sensations perceived during tasting.” In lay terms, smell + taste + mouthfeel = flavor.

  But that simple equation leaves out some crucial dimensions of flavor—dimensions that Hobkinson draws on in her multisensory feast, and that Spence has built a career around. A decade ago, for example, Spence did some of the pioneering work to show that our sense of hearing also contributes to flavor. In short, a steak’s sizzle is part of its flavor.

  Spence didn’t actually use steaks in his experiments—they’re expensive, and it’s difficult to standardize “sizzle” in the laboratory. Instead, he turned to a foodstuff that could have been designed expressly with experimental psychologists in mind: Pringles potato chips. Instead of being sliced from individual, idiosyncratically flawed potatoes, Pringles are formed from a uniform slurry of pulped starch (rice, wheat, corn—and, yes, potato), so every chip in every can is identical to the next one—a perfect, standardized experimental replicate.

  Spence and his associate Max Zampini asked twenty volunteers to munch their way through 180 Pringles each, rating the flavor of each chip, while wearing audio headphones that played back the sound of their crunching. As the volunteers soldiered on, a computer modified the playback sounds to make them quieter or louder, and to emphasize certain audio frequencies. The crunch, Spence found, was a key part of the chips’ flavor. When volunteers heard a louder crunch, or even just a louder high-frequency part of the crunch, they rated the chips about 15 percent crunchier and fresher tasting than when they heard quieter sounds. The finding was surprising—and amusing—enough to net Spence and Zampini an Ig Nobel Prize, a tongue-in-cheek research award for research that “first makes you laugh, then makes you think.” It’s a laurel that Spence continues to wear proudly, mentioning it often in his later scientific papers, and even listing it among his “Academic Distinctions” right at the top of his résumé.

  The same principle holds for other foods that feature distinctive sounds. Recently, for example, one group of researchers had volunteers rate the flavor of several coffees as they listened to sounds of a coffee maker in the background. Unknown to the tasters, every cup of coffee was actually identical—yet they rated the coffee 10 percent tastier when they heard sounds of a more “expensive” coffee maker (actually the same recording with annoying high frequencies muted).

  Probably the best known of these experiments, in the foodie world, at least, was a test Spence conducted with oysters. He asked eaters to rate the flavor of the oysters while listening through headphones to one of two soundtracks: either sea sounds such as crashing waves and shrieking seagulls, or barnyard sounds such as clucking chickens and mooing cattle. By now you won’t be surprised to learn that the eaters found the oysters tastier—and many people also found them saltier—when accompanied by the sea sounds.

  This experiment has found its way straight onto the plate at what many people consider the finest restaurant in the world: The Fat Duck, in the little village of Bray, England, not far west of London. You’ll find it just a few miles past Heathrow Airport, near the manicured grounds of Windsor Castle, where the queen likes to spend her weekends, and the famous playing fields of Eton, home to centuries of upper-class schoolboys.

  It’s not easy to get a table at The Fat Duck. Unless you can talk your way into a VIP table, you’ll need to call at the stroke of noon, UK time, on the first Wednesday of the third month before your intended date. If you’re lucky enough to score a reservation, expect to pay £255 (approximately $337, at the time of this writing) each, not including wine or tip. It’s a small fortune, but you’ll also spend four and a half hours savoring one of the most extraordinary meals of your life. Your menu might include an egg-white puff flavored with gin and tonic and frozen in liquid nitrogen, a quail jelly served alongside a bed of moss that emits forest-scented smoke as you eat, and something rather unpromisingly called “snail porridge.”

  But perhaps the most famous of chef Heston Blumenthal’s creations is a dish he calls “Sound of the Sea.” Your server sets before you a conch shell with a set of earbuds emerging from its opening. You put the buds in your ears and hear a soundtrack of crashing surf and calling gulls. Soon an edible seaside diorama arrives, with raw fish, seaweed, a seawa
ter foam, and “sand” made from ground-up fish, seaweed, breadcrumbs, and other binders. Just as Spence found with his oyster experiment, the seaside sounds you hear as you eat are not just background frills but an integral part of the flavor experience. You’re tasting not just with your mouth but with your ears as well.

  Even abstract sounds can affect the flavors we perceive, as shown by Hobkinson’s “sonic pop” dessert, where low-pitched sounds bring out the chocolate’s bitter notes and high-pitched ones accentuate its sweetness, for reasons Spence cannot yet explain. Words, too, have “flavors,” he’s found—people associate spiky-sounding words like kiki with bitter flavors and rounder-sounding words like bouba with sweet ones. Other researchers have shown that people expect a mythical ice cream called “Frosh” to taste richer and creamier than one named “Frish.”

  If squeals, rumbles, and words can alter flavor, the logical next step would be to ask whether music can, too—and the answer appears to be that it does. “Sound is the last sense that people think about when it comes to flavor,” says Spence, “but there’s a huge explosion of work showing that people match flavors to classes of instruments or pieces of music.” Heavy, powerful music such as Carl Orff’s “Carmina Burana” makes tasters notice the heavy flavors in red wine, for example, while “zingy” pop music such as Nouvelle Vague’s “I Just Can’t Get Enough” brings out the brighter flavors in white wine, he notes. A few food writers are already working on cookbooks that pair food and music in “musical recipes”—and Spence himself says he now gives a lot more thought to his choice of background music for dinner parties.

  He’s also paying more attention to the crockery he serves his meals on, thanks to some other research he’s done. As usual, this involved some trickery. In this case, Spence’s colleague Betina Piqueras-Fiszman asked fifty volunteers to evaluate three different yogurts, presented one at a time in apparently identical bowls. By now you probably see the trick coming: In reality, the three yogurts were all the same, but Piqueras-Fiszman had invisibly weighted some of the bowls to be heavier than others. Sure enough, the raters judged the yogurt in the heavier bowls as being both richer and more pleasurable than the identical yogurt served in a lightweight bowl.

  Even the color of the crockery can make a difference to flavor, Spence finds. In one test, for example, tasters rated a strawberry mousse as being sweeter when served on a white plate than on a black one. Most likely, he thinks, that’s just because the white plate shows off the bright red strawberry color more dramatically, and this ripe-fruit color triggers us to expect sweetness. It’s a simple effect, but hard to escape. As a result, says Spence, “I guess the black plates we used to serve on we no longer use.”

  Hobkinson was aiming for something similar in her dinner. The look and feel of forks carved from tree branches would subconsciously evoke associations with wildness, she hoped, thus enhancing the flavor of the venison. In effect, it’s a kind of visual and tactile rhyme intended to emphasize a flavor message, just as a poet’s rhyme emphasizes a verbal message.

  That kind of visual rhyme turns up over and over in the world of flavor, and it usually works by modifying our expectations. One study, for example, showed that a food’s color can profoundly affect our perception of the food’s sweetness, but not its saltiness. Presumably that’s because in the natural world, color signals whether a fruit is ripe and sweet or underripe and sour, but we have no similar color clues to saltiness.

  One experiment performed more than a decade ago—and now notorious among wine aficionados—showed just how powerfully our visually produced expectations can affect flavor, even for highly trained tasters. In this case, the victims were a set of budding wine professionals, fifty-four undergraduate students in the highly regarded enology program at the University of Bordeaux, France. One day, the students were given three glasses of wine—two red, one white—and asked to describe each wine’s aroma. For enology students, of course, this is a routine task, and the students set about it with their usual thoroughness, discerning familiar aromas such as raspberry, clove, and pepper in the two reds and honey, lemon, and lychee in the white.

  Gotcha! What the students didn’t know is that there were, in fact, only two wines in the test, one red and one white. The third glass, the other “red,” contained the same white wine, but researcher Gil Morrot and his colleagues had tinted it red with odorless food coloring. Simply changing the wine’s color had totally altered the students’ experience of the flavor. And remember, these were not naive, beer-swilling philistines, but people who were training for careers in the wine industry. (Their training might even have made them more prone to fall for the trick, because as experienced wine drinkers, they would have had stronger expectations linking color to certain flavors.)

  So far, we’ve talked as though these multisensory effects on flavor act by altering our expectations, and there’s no doubt that accounts for part of the effect. “When I smell a certain smell like strawberry, there’s an expectation that what’s coming next is going to be sweet,” says Spence. Similarly, we expect “red” wine to smell like red wine, yogurt in a heavier bowl to be richer and more satisfying, red foods to taste sweeter than green ones. And what we expect to find, we do.

  In this sense, everything about a meal’s context—the paintings on the walls, the lighting, the tablecloths, and more—helps to create an expectation of the meal to come, and this expectation probably biases our perception of its flavor. To illustrate this, Spence and his colleagues recently held a public event in London’s trendy Soho district where participants compared the experience of sipping a single Scotch whisky (The Singleton, for you Scotch geeks out there) in three different rooms. In the Nose Room, a green-lit space filled with leafy plants and the fragrance of cut grass, participants found that the whisky had a more pronounced grassy flavor. In the Taste Room, with red lights, rounded furnishings, and fruity aromas, the Scotch tasted sweeter. And in the Finish Room, a dimly lit, wood-paneled chamber redolent of cedar, its woody aftertaste became more prominent. All this, despite every participant knowing it was exactly the same whisky each time, because the cup never left their hand. Even circumstances that have nothing to do with food can bias our flavor perceptions. One study, for example, found that fans attending ice hockey games at Cornell University thought ice cream tasted sweeter after the home team won, and sourer after it lost!

  This “everything contributes to flavor” attitude is not a new one. The Italian Futurist movement of the 1930s famously took the notion and ran with it to bizarre extremes. Diners at the movement’s flagship restaurant, La Taverna del Santo Palato (the Holy Palate Tavern) in Turin, dined on olives and fennel hearts with their right hands (sans cutlery) while stroking sandpaper and velvet with their left—all while the headwaiter doused them with perfume. Another course featured a sea of raw egg yolks surrounding a meringue island and airplane-shaped slices of truffle. I’m not entirely sure what expectations the futurist chef was trying to create, but suffice it to say that it didn’t revolutionize Italian cuisine for very long.

  But these multisensory influences on flavor aren’t just a question of expectations. Even the faintest whiff of strawberry aroma—so faint it can’t be consciously detected—is enough to boost our perception of sweetness, several studies have found. If you can’t consciously smell the strawberry, you can’t consciously expect a sweeter taste. Instead, Spence thinks, what’s happening is something he calls “sensory integration.” At first pass, that sounds not much different, but as Spence points out, expectations have a cause-and-effect timing pattern, in which you first smell the strawberry and then expect to taste the sweetness. In sensory integration, on the other hand, the two sensations arrive at the same time and reinforce each other.

  You’ve experienced this kind of integration if you’ve ever watched someone’s lips to help you hear what they were saying at a noisy cocktail party. Even when neither hearing nor lip-reading alone would be enough to understand the conversation, you can do ju
st fine with both together. The simultaneity of sight and sound are crucial to doing this. “If you had the lip movements presented a half second ahead of the voice, the effect would disappear,” Spence says.

  This integration helps in understanding one of the great mysteries of flavor science, which you can experience for yourself right now. Take a bite or a sip of something flavorful—a rich stew, a ripe peach, a full-bodied wine—and take a moment to really savor it. Now, quickly, point to where the flavor is. Unless you’re very unusual, you pointed to your mouth, but you know from chapter 3 that most flavor comes from your sense of smell, which is in the nose. The illusion is so strong that even knowing this reality, as you now do, doesn’t change what you experience. So why does the flavor seem to happen in your mouth?

  Sensory neuroscientists actually spend a fair bit of time obsessing over questions like this, and over the years they’ve arrived at a plausible answer. One of the brain’s important jobs is to edit the raw stream of sensations, choose the relevant ones, and package them into concepts that we can think about. The timing of events is a valuable clue to that packaging: If two sensations occur together, they probably belong together. Ventriloquists exploit this tendency in their performances, by carefully timing their dummy’s lip movements to match the sounds of their speech. If the match is good enough, the audience’s minds will bind sight and sound together, leaving the strong illusion that the sound is coming from the dummy, not the human.