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We’re no strangers to seeking heat. And we’re not talking about the playful tingle of a jalapeño but the ugly, nose-drippy, sweating from your temples kind of heat you get from Szechuanese cuisine or Nashville-style hot chicken. In Flavor, science writer Bob Holmes, dedicates a whole chapter to why we avidly chase the pain of spice, how the Scoville scale works and what really is the best remedy for a burning mouth. Holmes, in the name of science and research, samples a jalapeño, Thai bird eye chili and habanero pepper. Read the excerpt below to find out how he fairs against the heat.

Reprinted with permission from Flavor: The Science of our Most Neglected Sense

The Pursuit of Pain

I’ve been procrastinating. On my dining room table I have lined up three hot peppers: one habanero, flame-orange and lantern-shaped; one skinny little Thai bird’s eye chili; and one rela­tively innocuous jalapeño, looking by comparison like a big green zeppelin. My mission, should I choose to accept, is to eat them. For you, dear readers.

In ordinary life, I’m at least moderately fond of hot peppers. My fridge has three kinds of salsa, a bottle of Sriracha, and a jar of Szechuan hot bean paste, all of which I use regularly. But I’m not extreme: I pick the whole peppers out of my Thai curries and set them aside uneaten. And I’m a habanero virgin. Its reputation as the hottest pepper you can easily find in the grocery store has me a bit spooked, so I’ve never cooked with one, let alone eaten it neat. (In fact, the first habanero I bought went moldy in my fridge while I was working up my courage.) Still, if I’m going to write a chapter that’s largely about hot peppers, I ought to have firsthand experi­ence at the high end of the range. Plus, I’m curious, in a vaguely spectator-at-my-own-car-crash way.

When people talk about flavor, they usually focus on taste and smell, just as we have so far. But there’s a third major flavor sense, as well, one that’s often overlooked: the physical sensations of touch, temperature, and pain. The burn of chili peppers is the most familiar example here, but there are others. Wine mavens speak of a wine’s “mouthfeel,” a concept that includes the puckery astringency of tannins—something tea drinkers also notice—and the fullness of texture that gives body to a wine. Gum chewers and peppermint fans recognize the feeling of minty coolness they get from their confections. And everyone knows the fizzy bite of car­bonated drinks.

None of these sensations is a matter of smell or taste (though of course Coca-Cola also tastes sweet and smells of caramel, cit­rus, and other flavors). In fact, our third primary flavor sense flies so far under our radar that even flavor wonks haven’t agreed on a single name for it. Sensory scientists are apt to refer to it as “chemesthesis,” “somatosensation,” or “trigeminal sense,” each of which covers a slightly different subset of the sense, and none of which mean much at all to the rest of the world. The common theme, though, is that all of these sensations are really manifes­tations of our sense of touch, and they’re surprisingly vital to our experience of flavor. Taste, smell, touch—the flavor trinity.

Sensory scientists have known for decades that chili burn is something different from taste and smell—something more like pain. But the real breakthrough in understanding chili burn came in 1997, when pharmacologist David Julius and his colleagues at the University of California, San Francisco, finally identified the receptor for capsaicin, the active ingredient in chili heat. The task demanded a lot of patience: Julius and his team took every gene active in sensory nerve cells, which respond to capsaicin, and swapped them into cultured kidney cells, which don’t. Eventually, they found a gene capable of making the kidney cells respond. The gene turned out to encode a receptor—eventually named TRPV1, and pronounced “trip-vee-one”—that is activated not just by capsaicin but also by dangerously hot temperatures. In other words, when you call a chili pepper “hot,” that’s not just an analogy—as far as your brain can tell, your mouth really is being burned. That’s a feel, not a smell or taste, and it passes to the brain through nerves that handle the sense of touch. Like other touch receptors, TRPV1 recep­tors are found all over the inner layer of your skin, where they warn you of burn risk from midsummer asphalt, baking dishes straight from the oven, and the like. But they can only pick up pepper burn where the protective outer skin is thin enough to let capsaicin enter—that is, in the mouth, eyes, and a few other places where the sun doesn’t shine. This explains the old Hungarian saying that “good paprika burns twice.”

Further tests showed that TRPV1 responds not just to heat and capsaicin but to a variety of other “hot” foods, including black pepper and ginger. More recently, several more TRP receptors have turned up that give other food-related somatosensations. TRPA1, which Julius calls the “wasabi receptor,” causes the sensa­tion of heat from wasabi, horseradish, and mustards, as well as onions, garlic, and cinnamon. TRPA1 is also responsible for the back-of-throat burn that aficionados value in their extra-virgin olive oil. A good oil delivers enough of a burn to cause a catch in your throat and often a cough. In fact, olive oil tasters rate oils as “one-cough” or “two-cough” oils, with the latter getting a higher rating. (One reason wasabi feels so different from olive oil is that the sulfur-containing chemicals in wasabi are volatile, so they deliver wasabi’s characteristic “nose hit,” while nonvolatile olive oil merely burns the throat. Olive oil may also trigger TRPV1 recep­tors to some extent.) Curiously, TRPA1 is also the heat receptor that rattlesnakes use to detect their prey on a dark night.

TRPM8—which is triggered by cool temperatures, rather than warm ones—is responsible for the cooling sensation of menthol (from mint) and eucalyptol (from eucalyptus). Food companies love TRPM8, by the way, because there’s a huge market for the mouthfeel of coolness in, for example, gums and mouthwashes. In fact, the menthol that used to make chewing gum minty fresh has largely been replaced by other molecules that do a more effec­tive job of triggering TRPM8, so that your gum holds its minty fla­vor longer.

Now that scientists understand the receptors that account for these perceptions, we can begin to unpack some of the subtleties of chili pepper flavor. Chili aficionados get pretty passionate about their pods, choosing just the right kind of chili for each applica­tion from the dozens available. The difference among chili vari­eties is partly a matter of smell and taste: Some are sweeter, some are fruitier, some have a dusky depth to their flavor. But there are differences in the way they feel in your mouth, too.

One difference is obvious: heat level. Chili experts measure a chili’s level of burn in Scoville heat units, a scale first derived by Wilbur Scoville, a pharmacist and pharmaceutical researcher, in 1912. Working in Detroit—not exactly a hotbed of chili cookery, especially back then—Scoville had the bright idea that he could measure a pepper’s hotness by diluting its extract until tasters could no longer detect the burn. The hotter the pepper was origi­nally, the more you’d have to dilute it to wash out the burn. Pepper extract that had to be diluted just tenfold to quench the heat scores ten Scoville heat units; a much hotter one that has to be diluted one hundred thousandfold scores one hundred thousand Sco­villes. Nowadays, researchers usually avoid the need for expen­sive panels of tasters by measuring the chili’s capsaicin content directly in the lab and converting that to Scoville units. The more capsaicin, the hotter the chili.

However you measure it, chilis differ widely in their heat level. Anaheims and poblanos are quite mild, tipping the scale at about 500 and 1,000 Scovilles, respectively. Jalapeños come in around 5,000, serranos about 15,000, cayennes about 40,000, Thai bird’s eye chilis near 100,000, and the habanero on my table somewhere between 100,000 and 300,000 Scovilles. From there, intrepid souls can venture into the truly hot, topping out—as of this writing—with the Carolina Reaper at a staggering 2.2 million Scovilles, which approaches the potency of police-grade pepper spray. Check out the online videos of hardy souls eating these peppers. “Successful” consumers sometimes end up in an ambulance. “They’re in pain, they swallow, they retch for a couple of hours. I miss the point,” says Bruce Bryant, who studies hot peppers and other mouthfeel per­ceptions at the Monell Chemical Senses Center. “I’m not a big pep­per eater,” he adds. “I was 30 years ago, but I don’t have anything to prove any more about how much pain I can stand.”

For those with an extreme mind-set, it’s worth noting that pure, unadulterated capsaicin packs a whopping sixteen million Sco­villes. If you’re looking for the ultimate in hot, though, a chemical called resiniferatoxin—found in a Moroccan spurge plant—delivers sixteen billion Scovilles in its purified form. That’s easily enough to cause lethal chemical burns. People don’t eat the stuff.

Returning to the culinary realm, many chili heads claim that a pepper’s heat is defined by more than just intensity. If any­one would know about this, I figured, it would probably be Paul Bosland, the director of the Chile Pepper Institute at New Mexico State University. Bosland’s institute has its fingers in all things chili—and, as a plant breeder by trade, he has a keen professional interest in all the tiny details of how chili heat differs from one pod to the next.

Bosland says he and his colleagues distinguish four other com­ponents to chili heat in addition to heat level. The first is how fast the heat starts. “Most people, when they bite the habanero, it maybe takes 20 to 30 seconds before they feel the heat, whereas an Asian chili is immediate,” he says. Chilis also differ in how long the burn lasts. Some, like jalapeños and many of the Asian varieties, fade rel­atively quickly; others, like habaneros, may linger for hours. Where the chili hits you also varies. “Usually, with a jalapeño, it’s the tip of your tongue and lips, with New Mexico pod types it’s in the middle of the mouth, and with a habanero it’s at the back,” says Bosland. And fourth, Bosland and his crew distinguish between “sharp” and “flat” qualities of burn. “Sharp is like pins sticking in your mouth, while flat is like a paintbrush,” he says. New Mexico chilis tend to be flat while Asian ones tend to be sharp—a quality I certainly noticed the last time I ate Thai food.

Some of that difference no doubt arises because chili burn is about more than just capsaicin. In fact, there are at least twenty-two different chemicals in the capsaicin family, each of which tickles the TRPV1 receptors a little differently. Nordihydrocapsa­icin, for example, seems to burn more at the front of the mouth, while homodihydrocapsaicin hits more at the back of the throat, explains Michael Mazourek, a chili breeder at Cornell Univer­sity. But the difference matters less than you’d think. Nordihy­drocapsaicin, for example, is only half as potent as capsaicin, and makes up at most 7 percent of the capsaicin content. “So you can see its vote doesn’t count for much, even though it would have some different properties,” says Mazourek. The two most common capsaicinoids—capsaicin itself and dihydrocapsaicin, which together make up 50–90 percent of the capsaicinoids in every pepper variety—are also by far the most potent, so they pretty much run the show.

A bigger reason why some peppers feel different from oth­ers, Mazourek thinks, may be something that food scientists call “matrix effects.” In order to perceive a pepper’s heat, the capsa­icin has to get out of the pepper’s cells and onto your tongue, lips, or palate. Pepper varieties with tougher cells would release their capsaicin more slowly as you chew, giving you a burn that builds more slowly, and perhaps hits you farther back in the mouth. Oil content might affect how quickly the capsaicin washes away, thus affecting the burn’s duration.

None of this explains the difference between “sharp” and “flat” chili heat, though. In fact, no one I talked to had a good explanation for this phenomenon. Mazourek and Julius both punted. Bosland suggested that different capsaicinoids could be involved, but he admitted he had no data to back up that con­jecture. And Bryant wondered whether everyone is just fooling themselves into thinking there’s a difference. “All you need to do is tell somebody that it’s going to be different,” he says. “I’m really skeptical about some of these reports.”

Okay, enough theory. I’ve put off my chili tasting as long as I could, and now it’s time to take the plunge. First up, the jalapeño. As you’d expect from its relatively wimpy ranking in the hot pep­per standings, it gives only a mild burn, which builds gently and mostly at the front of the mouth. (Score one point for Bosland.) Confronted with such a tame burn, I have plenty of attention left to focus on its thick, crisp flesh and sweet, almost bell-peppery flavor.

The Thai bird’s-eye chili, second on my list, is much smaller, and its flesh proves to be much thinner and tougher. Despite that, though, it almost immediately lets loose a blast of heat that explodes to fill my mouth from front to back, making me gasp for breath. No gradual build to this one—it’s a sledgehammer blow. If I think hard, I might imagine that the chili heat is a little bit sharper, pricklier, than the jalapeño. But I could just be fooling myself.

Finally, the one I’ve been dreading, the habanero. I cut a tiny slice (call me a coward—I never signed up for the full 300,000-Scoville experience) and start chewing. The first thing that strikes me is how different the flavor is. Instead of a vegetal, bell pepper flavor, the habanero gives me a much sweeter, fruitier impression that’s surprisingly pleasant. For about 15 or 20 seconds, anyway—and then, slowly but inexorably, the heat builds. And builds. And builds, long after I’ve swallowed the slice of pepper itself, until I can’t think of much else besides the fire that fills my mouth. It definitely hits farther back in the mouth than the Thai chili, though there’s a late-breaking flare-up on my tongue as well. The whole experi­ence lasts five or 10 minutes, and even now—a good half hour later—it’s as though coals are gently banked in my mouth. Wow.

Having set my mouth afire, I’d now like to quench the burn. Surprisingly, scientists can’t offer a whole lot of help in this regard. A cold drink certainly helps, because the coolness calms the heat-sensing TRPV1 receptors that capsaicin excites. The only problem—as you’ve no doubt noticed if you’ve tried to cope with a chili burn this way—is that the effect goes away in just a few sec­onds, as your mouth returns to normal body temperature.

Bob Holmes
Bob Holmes

You’ve probably heard, too, that sugar and fat help douse the fire, but the researchers themselves aren’t entirely convinced. “The best thing out there is probably cold, whole milk,” says John Hayes of the University of Pennsylvania. “The cold is going to help mask the burn, the viscosity is going to mask the burn, and the fat is going to pull the capsaicin off the receptor.” When pressed, though, he notes that there’s not a lot of data to back that up. Making a food more viscous has been shown to damp down taste—probably just because it provides a competing sen­sation to distract our attention, he notes, but he can’t think of anyone who’s tested whether it also reduces chili burn. And he’s not entirely sure that sugar really helps, either. “I’m not con­vinced that it actually knocks the heat down, or whether it just makes it more pleasant,” he says. Even the value of fats or oils— which sounds like they ought to help wash capsaicin, which is fat soluble, off the receptors—is in dispute. If you’re feeling the burn, says Bryant, the capsaicin has already penetrated your tis­sue, so a superficial rinse of whole milk or olive oil isn’t going to help much. Instead, Bryant has another suggestion: “Go kick a brick wall or take a hammer to your thumb. You’ll forget all about your tongue,” he says.

Bryant’s tongue is firmly in his cheek there. At least I think so, since I don’t know of any hot pepper fans who are actually tempted to smash their thumb with a hammer to cope with the burn. In a way, that highlights what might be the most fascinating aspect of chili peppers, wasabi, and their ilk. Millions of people actively seek out the pain of hot chilis as a form of pleasure. The burn fea­tures prominently in more than a few of the world’s great cuisines, with more than a quarter of the world’s population eating hot pep­pers daily. More than three quarters of Americans in one recent survey expressed an interest in eating hot chilis, and the British spend £17 million (approximately $22 million, at the time of this writing) annually on hot sauce.

And yet, only the oddest among us makes a similar fetish of inflicting other sorts of pain. We don’t take pleasure in eating food that’s still searingly hot from the oven, even though that delivers exactly the same sensation we get from chilis: same receptors, same nerves. We don’t choose to chemically burn our tongues with strong acids. We don’t hammer our thumbs for fun. So why do we happily, even eagerly, inflict pain by chilis? Whatever the secret is, it seems to be unique to humans. No other mammal on the planet has a similar taste for chilis. (Birds eat them enthusiastically, but only because they lack receptors that respond to capsaicin. To a par­akeet, the hottest habanero is as bland as a bell pepper.)

One possible explanation is that chili lovers simply don’t feel the pain as intensely as those who shun hot peppers. In the lab, it’s certainly true that people who are repeatedly exposed to cap­saicin become less sensitive to it. In fact, liniments such as Heet and Icy Hot contain capsaicin for its painkilling properties. It’s easy to imagine that something similar might be happening to chili eaters, too, because people who eat hot peppers more often report less burn from a given test dose of capsaicin. But when you look more closely at that result, it gets less convincing. For one thing, an inexperienced chili eater might think a sample is the hottest thing they’ve ever eaten and rate it nine out of ten for burn (“I could light a cigarette from my mouth!” a shocked Romanian friend exclaimed once during an Indian dinner), while an old hand might say, “Hah, I’ve had hotter,” and give the same sample a five. Alert researchers can avoid this problem by following Linda Bartoshuk’s lead and pegging the upper end of the scale as “the most intense sensation of any kind you’ve ever experienced,” but not every study does so.

Genetics may play some part, too. Studies of identical twins (who share all their genes) and fraternal twins (who share only half) suggest that genes account for between 18 and 58 percent of our liking for chili peppers. Some people may have more sensi­tive TRPV1 receptors, for example—though Hayes, who’s looking into that now, says, “The jury is really still out on whether there is meaningful TRPV1 variation.” Similarly, some (but not all) studies have found that chilis cause more pain in supertasters or those with more fungiform papillae (and therefore, presumably, more pain nerve endings) on their tongue.

It’s abundantly clear, though, that chili lovers aren’t immune to the pain. Just ask one. “I like it so all my pores open up and tears are rolling down my face,” says Hayes. “But with two young kids in the house, I don’t get that very often.” For now, Hayes gets his pain mostly from a handy bottle of Sriracha hot sauce. “My kids refer to it as Daddy’s ketchup,” he says.

It’s clear from listening to Hayes that he—and probably most other chili eaters—actively enjoys the pain. That paradox has drawn the attention of psychologists for several decades now. Back in the 1980s, pioneering chili researcher Paul Rozin of the University of Pennsylvania proposed that chili eating is a form of “benign masochism,” like watching a scary movie or riding a roller coaster. After all, most forms of pain are warnings of imminent harm. That baked potato still steaming from the oven is hot enough to kill the cells lining your mouth, potentially caus­ing permanent damage. The hammer landing on your thumb can break bones. But chili burn—except at its uppermost, million-Scoville extreme—is a false alarm: a way to get the thrill of living on the edge without the risk of exposing yourself to real danger.

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 20 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 20 and 80, 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—30 out of 40 —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 50-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 six­pack 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 vol­unteers 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.