by Bob Holmes
A few decades later, Hayes and his student Nadia Byrnes (perhaps the best name ever for a hot pepper researcher) took Rozin’s ball and ran with it. If chili heads are looking for thrills, Byrnes and Hayes reasoned, you’d expect them to have sensation-seeking personalities. And, sure enough, when they went to the vast arsenal of “instruments”—that is, personality tests—that psychologists have developed to measure facets of personality, they found several measures of sensation seeking, of which the latest and best was the Arnett Inventory of Sensation Seeking. Then they set out to see whether chili lovers really do crave excitement.
As a chili eater, I have a personal stake here, so I found the Arnett Inventory on the Internet and took the test myself. It’s only twenty questions long. Each question gives a statement about yourself (examples include “When I listen to music, I like it to be loud,” “It would be interesting to see a car accident happen,” and “I would have enjoyed being one of the first explorers of an unknown land”) and asks you to score it on a four-point scale from “does not describe me at all” to “describes me very well.” Add up the scores, and there you have it: one number, somewhere between twenty and eighty, that summarizes your yen for stimulation. Of such bricks is the edifice of personality research built. (Actually, Arnett gives you two subscores, as well: one for novelty seeking, and the other for intensity seeking. I scored high—thirty out of forty—for the first, and very low—just nineteen—for the second. I’m not a psychologist, and self-diagnosis is dubious in any case, but that fits: I’m eager and willing to visit a new place or eat a new kind of food, but terrified by roller coasters and irritated by overly loud music.)
Sure enough, when Byrnes and Hayes tested nearly 250 volunteers, they found that chili lovers were indeed more likely to be sensation seekers than people who avoided chilis. And it’s not just that sensation seekers approach all of life with more gusto—the effect was specific to chilis. When it came to more boring foods like cotton candy, hot dogs, or skim milk, the sensation seekers were no more likely to partake than their more timid confreres.
Chili eaters also tended to score higher on another aspect of personality called sensitivity to reward, which measures how drawn we are to praise, attention, and other external reinforcement. And when the researchers looked more closely, an interesting pattern emerged: sensation seeking was the best predictor of chili eating in women, while in men, sensitivity to reward was the better predictor. Hayes thinks that’s because machismo plays a role in the chili eating of men, but not women. “For women, there’s no social status to being able to eat the hottest chili pepper, while for men there is,” he speculates. Without the heavy hand of machismo on the scales, women’s chili eating is more strongly governed by their internal drive for excitement.
Incidentally, while chili lovers laud the rush they get from a spicy dish, and sometimes claim the peppers “wake up” their palate to other flavors, you’ll often hear chili-averse people complain that the burn keeps them from savoring other flavors in their meal. Which is it? The matter has received surprisingly little scientific study, but the bottom line seems to be that if capsaicin blocks other flavors, the effect is small. Most likely, when people complain that they “can’t taste as well” after a spicy mouthful, it’s largely because they’re paying so much attention to the unfamiliar burn that the other flavors fly under the radar. In other words, it’s not “hot” but “too hot” that interferes with the enjoyment of flavor—and the threshold where hot becomes too hot is a very personal one.
While chilis get most of the attention at the touch-related end of flavor, they aren’t the only game in town. Of the others, one of the most intriguing is the tingling sensation from Szechuan pepper, a common ingredient in Chinese, Indian, and Nepalese cooking. If you haven’t experienced this unique feeling, I encourage you to try it. You can find Szechuan peppercorns—which, despite the name, are neither chili nor black pepper, but flower buds of a member of the citrus family—in Asian groceries and specialty stores. They look like little brown Pac-men. Put a pinch in your mouth and chew for a moment, making sure it makes good contact with your tongue, and then wait a few minutes. At first, you might get a little hotness reminiscent of black pepper, but that’s quickly replaced by a tingling sensation that’s like nothing else you’ve ever experienced. Some people describe it as similar to touching your tongue to the terminals of a nine-volt battery. Others say it’s like a vibration. “It’s truly a crazy sensation,” says Chris Simons, a food scientist at The Ohio State University who has studied it. “It doesn’t hurt, it’s not painful or irritating like capsaicin. You put it on your tongue and it actually buzzes.” Specifically, the buzz is like a fifty-hertz vibration, as British researchers discovered when they asked people to match the feel of Szechuan pepper to a mechanical vibrator on their fingertip. If you have a piano handy, that’s roughly the frequency of the lowest G, the seventh white key from the left.
The details aren’t fully understood yet, but it looks like the active ingredient in Szechuan pepper, sanshool, blocks the flow of potassium out of nerve cells. This outward trickle of potassium acts to suppress nerve activity, so, in effect, sanshool tickles the nerves so that they’re more likely to fire randomly. This case of neural jitters accounts for the buzzy feeling. Pharmaceutical companies are studying the same potassium channels as a target for painkilling drugs—and, in fact, after fifteen or twenty minutes, the buzz of sanshool gives way to a numbness that lasts for another quarter hour or so. This numbness can block some of the pain from chili peppers, Simons has found. Indeed, this may be one reason cooks began adding Szechuan pepper to their dishes, he speculates.
If your tastes run like mine, you’re probably tempted to wash your Szechuan-pepper-laden mapo tofu down with a mug of cold beer. Good choice, because the fizzy bite of beer and soft drinks on your tongue is another common example of the mouthfeel side of flavor. If you’ve ever stopped to think about this sensation, you probably assumed that carbonation’s bite is all about the bubbles. Until recently, most scientists thought so, too. “When I first started working with this, they said it’s the popping of the bubbles on the tongue that makes the bite,” says Bryant. But then Bryant chanced across a copy of a medical journal that made him rethink that simple story. The journal contained a letter from a doctor who was also a high-altitude climber. Like many such climbers, he took a drug to combat altitude sickness while on the mountain. On the particular climb in question, he had hauled a celebratory six-pack of beer up with him. When he cracked a bottle at the summit, he found that it had plenty of fizz but lacked the familiar bite. Intrigued, he and a colleague tested the effect back at sea level—and sure enough, the altitude-sickness drug completely negated the bite of carbonation, even though the bubbles were still there.
The key to this puzzle is that altitude-sickness drugs inhibit an enzyme called carbonic anhydrase, which converts carbon dioxide—the gas that forms the bubbles in carbonated drinks—into carbonic acid. In the glass, CO2 changes to carbonic acid very slowly, but once it gets into your mouth, carbonic anhydrase drives the reaction much faster. Since the drugs knock out carbonation’s bite, that suggests that it’s not the bubbles but the carbonic acid that is responsible for the bite.
Bryant and his colleague Paul Wise figured there was another way to test this idea, by keeping the CO2 but eliminating the bubbles. “We took some seltzers and some beers into a hyperbaric chamber and cranked it up to 2 atmospheres,” he recalls. The increased pressure kept the bubbles dissolved in the liquid, just as though they were still sealed in the bottle. “The seltzer had no bubbles and the same bite as when you drank it at normal pressure with bubbles.” So much for popping bubbles. Instead, it seems that carbonation bite is all about the acid burn, yet another sensation largely detected by TRPV1 receptors.
But something still nagged at Bryant, because he couldn’t abandon the notion that bubbles were somehow part of the experience. So he and Wise tried another test, this time giving volunte
ers a mildly carbonated water, enough to generate a tiny bite but not enough to make noticeable bubbles. Then they slipped an aquarium air stone, the little, porous device used to aerate fish tanks, under the volunteers’ tongues to add some bubbles—pure bubbles, no acid—to the experience. “We were essentially tickling the tongue with bubbles,” he says. “And that increased the reported bite of the carbonation.” It’s not clear yet whether that’s just because we expect the bubbles to be accompanied by a bite, or whether something else is going on as well.
So far, we’ve been talking about sensations that work much like smell and taste do, with nerve cells detecting the presence of particular chemicals—capsaicin, menthol, sanshool, acid—in a bite of food. The only difference is that in these cases, the information passes via touch nerves, rather than smell or taste nerves. But there are other layers in the mouthfeel sandwich, too, that are more a matter of touch in the usual sense—most notably, astringency. To appreciate this sensation, you just have to sip strong black tea or a tannic red wine—a young California cabernet, say—or eat an unripe banana. Recognize that dry, puckery feeling in your mouth? That’s astringency. It happens when tannins and other compounds called phenolics in the food glom on to proteins in your saliva and prevent them from carrying out their usual lube job on your mouth and the food you’re chewing. (If you put milk in your tea, your cup of tea is less astringent because the proteins in the milk tie up the phenolics before they can get to the salivary proteins.)
The perception of astringency may explain a lot about why certain foods go so well together. Think of red wine with steak; sorbet after rich, creamy soup; pickles with sausage; green tea with oily stir-fried pork and vegetables. Each of these pairs an astringent food or drink—often referred to as a “palate cleanser”—with one that’s loaded with fat. Could fat and astringency be a culinary yin and yang, complementary opposites that bring out the best in each other?
The question intrigued Paul Breslin, the Monell researcher who makes a habit of bringing his intense curiosity and enthusiasm to the dining table. A few years ago, Breslin and his colleagues decided to put this notion of palate cleansing to a rigorous test in the lab. To avoid all the complicated messiness of real foods, with their many ingredients, Breslin’s team asked volunteers to sip standardized astringents—extracts of grape seeds or green tea—and describe the feeling in their mouths. The volunteers reported that the sensation of astringency built up over repeated sips, so that even a mildly astringent drink eventually became intensely puckery. But when the volunteers alternated bites of fatty dried meat with their sips of tea, each one kept the other in check. The fattiness of the meat tamed the tea’s astringency, and the tea “cleansed” the palate of the meat’s greasy feel. Remember that sip of wine the next time you grill a rib-eye steak.
Of course, now and then you find a food that manages to be both lubricating and astringent at the same time—chocolate being the prime example. That makes Hayes wonder whether delubrication is the whole story in astringency. If all that cocoa butter lubricating your mouth isn’t enough to wipe out astringency, maybe we’re detecting astringents more directly, too. Sure enough, German researchers—together with Linda Bartoshuk—recently reported the first hints that a receptor could also be involved in perceptions of astringency. The question remains open so far.
The fatty end of the equation, on the other hand, seems to be purely a matter of texture. As we’ve seen, our sense of taste picks up the nasty, rancid fatty acid part of fats, but not the rich, creamy, luscious whole. Instead, when we savor a buttery sauce or a bowl of ice cream, we’re detecting the fat merely as a smooth, viscous coating in the mouth, a sensation picked up by ordinary touch receptors on the tongue and lips.
At this point we start to move beyond the so-called chemical senses of taste, smell, and receptor-based somatosensory perceptions like chili burn. In this wider world, our ordinary senses of touch, vision, and hearing have important roles to play as well. Just think of the difference between a crunchy potato chip and a soggy one, or a broccoli spear cooked just al dente versus one that’s overcooked to mush. “Of the foods I like the most, certainly taste and smell are central, but on equal footing are things like lubrication, crunch, and chewiness,” says Breslin. “If you think about how important texture and fattiness and creaminess and lubrication and even crunchiness are to what we eat, if you took those things away, it just wouldn’t be enough.”
Most people consider these textural attributes to be something separate from a food’s flavor. I know I thought that way at the outset. But once these sensations get to the brain they’re not so different after all.
Chapter 4
THIS IS YOUR BRAIN ON WINE
Among the countless restaurants that have come and gone on Upper Street in the trendy Islington district of London, the House of Wolf may have been the strangest. The nondescript, three-story gray brick building with a large mullioned window on the ground floor was once a Victorian music hall. Today, it has morphed into a nightclub called The Dolls House, but a few years earlier, it was what its owners called “a multi-functional, multi-sensory pleasure palace, dedicated to the creative pursuits of dining, drinking, art and entertainment.” The rest of us called it London’s most experimental restaurant. Its kitchen featured a predictably unpredictable parade of avant-garde guest chefs, each holding the stove for just a month or two before yielding to the next visitor.
If you had been lucky enough to stumble on the House of Wolf when it first opened in October 2012, you would have experienced one of the most peculiar meals of your life. As you enter the dining room, you’re greeted by the sight of bread rolls dangling by strings from helium balloons floating at the ceiling. The chef—artist Caroline Hobkinson—instructs you to put in earplugs, then eat your roll off the string without using your hands. As you nibble away—rather like bobbing for apples in midair—you hear the crunch of the crust, magnified by the plugs in your ears. “Can you hear the taste?” Hobkinson asks in the printed menu.
For the next course, you don a blindfold. Your waiter brings you a cracker topped with warm goat cheese redolent of rosemary and roasted red peppers. After your first bite, you remove the blindfold and see that the rosemary and pepper aren’t on the cracker at all—they had merely been wafted before your nose as you ate the cracker and unflavored cheese. “Can you see the taste?” Hobkinson’s menu asks.
No blindfolds or earplugs for the next course. Instead, your waiter sets before you a plate of salmon sashimi and a syringe filled with an amber liquid. Following instructions, you inject the fish with the liquid, which turns out to be ten-year-old Ardbeg, an intensely peaty Scotch whisky. Magically, the aroma of peat smoke from the whisky transforms the flavor from raw fish into smoked salmon. “Can you smell the taste?” the menu asks.
After a palate cleanser—a gin-infused cucumber ice, which you eat alternately with two spoons, one coated with salt crystals and the other with rose water crystals, giving two odd textures to your tongue—comes the main course, a straightforward, classic loin of venison with mushrooms, prunes, and wild cherries. Ah, you think, something normal at last. Well, not quite. Instead of a fork, the waiter brings you a tree branch as long as your arm, with the thick end carved into a forked prong. Like a Stone-Age hunter, you spear the meat with the branch and bring it to your mouth. “Can you feel the taste?” Hobkinson asks.
The final course, dessert, is a “sonic cake pop,” a spherical chocolate brownie on a lollipop stick. It is served with an unusual garnish: a telephone number. You pull out your cell phone, dial the number, and hear instructions to press “1” for bitter or “2” for sweet. Depending on your choice, you’ll hear a low rumble or a high whine—and the sound makes the dessert taste either bitter or sweet. “Can you dial a taste?” Hobkinson asks.
It all sounds a bit over the top—more performance art than meal. And at one level, of course, it is. But as with most art, there’s a deeper message here, and Hobkinson is doing much more th
an just playing with our preconceptions about the dining experience. Her eccentric banquet also draws on a lot of solid science as it stretches our concept of flavor to include sight, sound, touch, and even thought. In fact, perceptual scientists can make a strong argument that a food’s flavor isn’t really contained in the food at all. Instead, you construct flavor in your mind from the whole range of senses you experience with each bite—and each of the courses in Hobkinson’s meal is carefully designed to illustrate some part of that creative process.
Hobkinson’s behind-the-scenes collaborator in all this is Charles Spence, a psychologist at Oxford University. A well-built man with a receding head of wispy hair, a deeply cleft chin, and a slightly protruding lower lip, Spence has the enthusiastic, self-satisfied air of someone who loves his work. And why wouldn’t he? As one of the world’s leading experts on what he calls “multisensory perception,” Spence is forever playing with his food to better understand why things taste the way they do and how chefs, industrial food companies, and ordinary home cooks can heighten the flavor of the food they prepare. Along the way, Spence has collaborated with some of the best chefs in the world, including England’s Heston Blumenthal and Spain’s Ferran Adrià. Spence is one of the few scientists with the clout to command a VIP table at almost any high-end restaurant in the world.
Like many star scientists, Spence took a backdoor route into the research that made him famous. He was always interested in multisensory perception, but at first he focused on the better-studied senses of sight, sound, and touch. Back then, in the 1990s, hardly anyone worked on such “minor” senses as taste and smell. “It seems very bizarre, but most psychologists have only been interested in the so-called higher senses,” he says. “There isn’t much to read about food and flavor.” But early on, he landed a few grants from food companies such as Unilever to apply the multisensory approach to flavor. Soon he was hooked, for both personal and professional reasons. “Food and drink are among life’s most enjoyable activities, and they are the most multisensory, as well. It’s an obvious place for a psychologist to end up,” he says.