Flavor Page 2

  From our senses to the kitchen, flavor is a much deeper and more complex subject than most people realize. In these pages, I provide what you can think of as a user’s guide to your flavor senses. By the end, I hope you’ll have a better understanding of what flavor is, how we perceive it, and how we can use that knowledge to enjoy a richer flavor experience.

  Flavor is a book for anyone who enjoys flavor—that is, for almost anyone. You don’t have to be a flavor virtuoso to find a deeper appreciation of what’s on your plate or what’s in your glass. I’m certainly no virtuoso. I’m just an amateur cook of middling ability and above-average enthusiasm, with a nose of roughly average ability. If I can find my way into a world of high-definition flavor, anyone can.

  Chapter 1

  BROCCOLI AND TONIC

  As a journalist, and a classically polite Canadian, I don’t often stick my tongue out at the people I’m interviewing. It seems bad form, somehow. But I’m doing it now to Linda Bartoshuk, the grande dame of taste research. Fortunately, she doesn’t seem to mind.

  “Oh, your tongue is gorgeous,” she gushes. She leans close and paints the tip of my tongue with a Q-Tip dipped in blue food coloring, which highlights the taste buds on my tongue. (To be accurate, they’re not actually taste buds, which are microscopic. Those mushroom-shaped bumps on the surface of the tongue that most people call taste buds are, technically speaking, really fungiform papillae, an impressive-sounding Latin term that means “mushroom-shaped bumps.”)

  I hold up a mirror to see what Bartoshuk sees on my tongue. Tiny pink islands stand out in a sea of blue dye. “You see those red dots on the front? Those are fungiform papillae,” she says. “You have a lot. Oh, and you have them all the way back! You’re very close to a supertaster.”

  Understanding this notion of the supertaster—that some people have a much more acute sense of taste than others—is what has brought me to Bartoshuk’s lab here at the University of Florida in Gainesville. It was Bartoshuk who first suggested, back in 1991, that people tend to fall into three groups, based on their ability to taste a bitter compound known as propylthiouracil, or PROP.

  You may have encountered PROP in a high school biology lab or at a science museum somewhere. You’re handed a little piece of filter paper infused with a modest amount of PROP, which you put on your tongue. Some people—the nontasters—just shrug, tasting basically nothing apart from filter paper. Others—the tasters—notice an unpleasant bitter taste, while the third group experiences extreme bitterness. This third group, the supertasters, are easy to recognize: They’re the ones who make an anguished face and rush off to find something—anything—to wash that horrible taste out of their mouth. Bartoshuk often asks people to rate the intensity of PROP’s bitterness on a scale from 0 to 100, where 100 is the most intense sensation they’ve ever experienced—the pain of childbirth, say, or a broken bone, or the visual sensation of looking directly at the sun. Supertasters often rate the bitterness of PROP in the 60–80 range, nearly in broken-bone territory. Sure enough, I’d score it a 60: nasty, but not debilitating. “That’s into supertaster territory,” says Bartoshuk. “That’s in the area where you’re not screaming, but you’re definitely much higher than normal, and your tongue looks it.”

  And it’s not just bitterness. Supertasters tend to rate sweets as sweeter, salt as saltier, and chili peppers as hotter. They even report that food aromas are more intense, says Bartoshuk—probably because taste and smell reinforce each other in the brain.

  Before I get too smug about my taste acuity, though, Bartoshuk points out that supertasters tend to be pretty boring eaters. Most of them prefer to avoid the intense taste experiences that come with highly flavored foods, so their diets are often bland and narrow. (I knew a man once who lived on a habitual diet of lima beans and milk. I would bet good money he was a supertaster.) In particular, bitter greens and other vegetables don’t show up very often on the plates of most supertasters.

  That’s where I start to get confused, because that doesn’t sound like me. I love collard greens, rapini, and other bitter vegetables; I always pick the hoppiest beer I can find; I drink my coffee black and without sugar; tonic water is my soft drink of choice—indeed, the only one I ever drink. In contrast, Bartoshuk—a nontaster—has very pronounced food aversions. She detests tonic water, for example. “When I first tasted it, I couldn’t believe it was a beverage,” she says. “I cannot stand greens. The bitter taste is just beyond belief to me.”

  So what’s going on? It’s time to look more closely at this whole supertaster notion, which turns out to be more complex than it appears at first glance.

  A little background: Even though we talk loosely about “tasting” complex foods like wine and cheese, most of their flavor actually comes from our sense of smell. In fact, even though we usually treat smell and taste as one and the same, they actually have different jobs to do. Smell is all about identification—it answers the question, “What is it?” It tells you the difference between rosemary and oregano, Brie and Stilton, or Cabernet Sauvignon and Pinot Noir. It tells you when something is burning on the stove, and it tells you that the dog needs a bath. We can even recognize the odor of our own bodies and those of our sweethearts.

  Taste, in contrast, answers a different question: “Do I want to eat this?” Taste is all about broad categories of good and bad, the yes/no, red-light/green-light decisions that would have been so crucial for our hunter-gatherer ancestors. As omnivores without access to grocery stores, they had to make these calls every day, and our taste repertoire bears witness. Everyone knows the “four basic tastes”: sweet, salty, sour, and bitter. If you’ve been paying attention the past few years, you’ve probably heard of a fifth: umami, a Japanese term that means “delicious flavor” and is usually translated as “savory,” “brothy,” or “meaty.” (There might be additional basic tastes, too, as we’ll see.) A closer look at each of those five tastes reveals a lot about what was important to our ancestors.

  Sweet tastes, most obviously, mark the presence of sugars, an important source of calories. Even starchy foods such as potatoes and grains yield a hint of sweetness as we chew, because enzymes in our saliva break down the starches into sweet-tasting sugars. Umami comes from amino acids—in particular, one called glutamate, though others contribute as well—that indicate the presence of proteins, another major class of nutrients. And our taste for salt would have helped our ancestors identify the electrolytes that were so precious and hard to find before salt shakers sat on every table. Hardly surprising, then, that we’re hardwired, even as infants, to be drawn to sweet, umami, and salty tastes.

  But taste also warns us when we’re about to eat something that might be harmful. Many toxins taste bitter, so we’re hardwired to reject bitter foods. Just watch the face of a toddler who unknowingly sips from a glass of tonic water—or, for that matter, an adult who gets surprised by a bitter-tasting berry or a first taste of aquavit or Fernet-Branca. The bitterness triggers our poison-avoidance reflex, and we make a “yucky face,” sticking out the tongue in a reflex that pushes the threatening food out of the mouth. Similarly, we tend to reject sourness, which could signal spoilage or unripe, indigestible fruit. With experience, and practice, we often learn to override that hardwiring for certain foods—coffee, hoppy beers, brussels sprouts, sour candy—but few, if any, people like them right away. Remember your first sip of coffee?

  Other species, with narrower diets, have fewer decisions to make and can often get by with fewer tastes. In the use-it-or-lose-it world of evolution, that often means they lose those extraneous tastes. Cats, for example, are entirely carnivorous, so they would never need to recognize high-sugar foods—and, in fact, they seem indifferent to sweetness. Sure enough, when researchers looked more closely, they found that cats have lost a crucial gene that would allow them to taste sweetness. Other carnivores, such as otters, sea lions, and hyenas, have also lost the ability to taste sweet. In each case, a different genetic defect was responsible
, suggesting that the taste for sweet has been lost several different times on the evolutionary tree—presumably, each time an omnivorous ancestor switched to an exclusively carnivorous diet. In contrast, pandas, which eat nothing but bamboo, have no need to detect protein in their diet and have lost the taste for umami. Other scientists recently discovered an even more extreme example of taste loss: vampire bats, with their blood-only diet, live in a taste world focused so tightly on recognizing the saltiness of blood that they lack the ability to taste sweet, umami, or bitter.

  And by the way, while we’re talking tastes: You’ve no doubt seen one of those “taste maps” of the tongue that purports to show that we taste sweet at the tip, salty and sour along the sides, and bitter at the back. If you’re up to date on your reading, you may also have heard that it’s completely wrong. As it turns out, though, both sides of the debate are guilty of a little exaggeration. There do seem to be minor differences in sensitivity to the various tastes across the tongue, with some regions a little more sensitive to sweet and others a little more sensitive to bitter, but the differences probably don’t matter much. And you can easily verify that the tastes aren’t tightly segregated into distinct zones, simply by dipping a Q-Tip in salt water and painting the tip of your tongue. You’ll taste the saltiness, even though you’re in what’s supposed to be the “sweet” zone. Best to just forget the whole notion of the taste map.

  Those five basic tastes seem like a pretty unimpressive set compared with the vast array of aromas we encounter in our food. Is taste really all that important to us, or is it only a minor part of our flavor experience? To answer that question, I headed from Bartoshuk’s lab in Florida to the Monell Chemical Senses Center in Philadelphia.

  You could think of Monell as the Vatican City of flavor research, but without the fancy architecture. The nondescript brick office building, on the fringes of the University of Pennsylvania campus just west of downtown, could house anything: doctors’ offices, accountants, engineers. Only a giant bronze sculpture of a nose and mouth, on a concrete plinth next to the front door, hints that something more unusual is inside: one of the planet’s greatest concentrations of researchers on the basic biology of the flavor senses.

  Inside, Monell’s boardroom looks much as you’d expect for such an august institution: long, dark wood table polished to a high gloss, high-backed leather chairs, off-white walls hung with framed memorabilia and interesting-but-not-too-interesting art. It all adds up to a clear message: significant discussions of important ideas take place here.

  Over the years, many of those ideas have come from Gary Beauchamp, the center’s longtime director. (He stepped down in 2014.) Beauchamp is a small, dapper man with silver hair, a neatly trimmed goatee, and a dignified manner. It’s easy to imagine him charming a sizable check out of a deep-pocketed donor. Right now, though, he’s leaning back in his chair at the head of the table, gazing thoughtfully at the ceiling. “Glaarglglglgl,” he says gently.

  “Glaarglglglgl,” we all gargle in response. We each lean forward to spit into a plastic cup, then wipe stray droplets from lips and face.

  This peculiar boardroom meeting had its genesis at a conference three months earlier, where I met Beauchamp for the first time. We’d been talking about the relative importance of taste versus smell in determining flavor. Most experts come down rather heavily on the side of smell as carrying the lion’s share of flavor, since it carries so much more information than just sweet, sour, salty, bitter, and umami. Some say smell accounts for 70 percent of flavor; others put it at 90 percent or more.

  But Beauchamp wasn’t buying it. In fact, he disagreed vehemently when I suggested this at the conference. “Clearly, olfaction is very, very important,” he said. “But the idea that it’s 70 percent of flavor is complete bullshit, in my view.” Olfaction gets all the attention, he went on, because we all know what it’s like to lose the sense of smell. Anyone who’s ever had a head cold knows that a plugged nose makes food bland and tasteless (though in fact, “tasteless” is actually the exact opposite of the truth—what you’re experiencing is taste alone, in isolation, with smell taken out of the equation). And the jelly bean test gives an even more dramatic demonstration, because it’s so quickly reversible.

  On the other hand, most of us have never had the inverse experience, since nothing in our everyday life can take away the sense of taste while leaving smell intact. There is no reverse jelly bean test where you can hold your tongue to keep yourself from tasting. Doctors, too, often see patients who have lost their sense of smell as a result of head injury, viral infection, or just as a consequence of aging. By contrast, relatively few people lose their sense of taste. The big exception is cancer patients who undergo radiation to their head and neck, which often damages taste receptors and nerves. And their experience tells a terrible story, said Beauchamp, whose wife’s uncle was one of the unlucky ones: as bad as it is to lose your sense of smell, losing taste is far, far worse. “When people lose their sense of taste, they don’t eat. They starve themselves to death,” he said. “My view is that taste is absolutely the bedrock of flavor.”

  Moreover, Beauchamp thought he had a way to test that claim—an experiment that would be, in effect, something fairly close to a reverse jelly bean test. Certain drugs, it turns out, can block the perception of salt and sweetness, two of the most important tastes in many meals. “When those things are gone, my guess would be that your dinner would be absolutely awful,” Beauchamp said. He’d taken the salt-blocking drug before, out of curiosity, but had never tried knocking out both tastes at once. We agreed that it would be an interesting test to try sometime.

  Which brings us back to the Monell boardroom, several months later. Beauchamp, two of his colleagues, and I are gargling with chlorhexidine, an over-the-counter mouthwash sometimes used to treat gum disease, which has the odd side effect of blocking the taste of salt. Each of us tosses back four little cough-syrup cups of the bitter-tasting stuff, one after another, swishing each around in our mouth for thirty seconds and gargling occasionally to make sure the solution reaches well back in the throat, before spitting it out. We follow that with four more cough-syrup cups of a swampy-flavored tea made from a South American plant called Gymnema, which knocks out sweet taste.

  Sure enough, all that gargling and swishing seems to have obliterated those two tastes. A sip of Pepsi yields a brief prickling on my tongue—the mouthfeel, or touch, sensation from the carbonation—then its flavor vanishes completely. I dip my finger in salt crystals and lick it off: nothing, except a tiny residual saltiness at the very back of my throat where the chlorhexidine didn’t quite reach. Now we turn to our experimental “lunch,” a burger and fries from the food truck parked in front of the building, now quartered into individual servings. Without the most important parts of our sense of taste, would we be able to stomach the meal, or would we, like Beauchamp’s wife’s uncle, just give up?

  Sure enough, downing the burger is like eating a mouthful of textured clay or soft plastic pellets. Have you ever accidentally left the salt out of homemade bread and been bored by the blahness of the resulting loaf? This burger is like that, but much more so—and we’ve only knocked out two of the five basic tastes. When I eliminate smell, too, by pinching my nose shut, it’s even worse: a totally nondescript experience. But even the loss of taste alone is really crippling—much worse than doing without smell, as I have when eating a burger while nursing a cold. So it looks like the burger, at least, bears out Beauchamp’s theory that taste trumps smell.

  The fries, though, aren’t so bad—partly because I get a little residual saltiness at the back of my tongue, where the gargle didn’t reach, but partly because there’s still something interesting going on when I put them in my mouth. Could this be the “fat taste” that many researchers now think belongs in the canon, or the fat’s pleasant mouthfeel? Then, too, the ketchup still gives a pleasantly tart/umami kick, though it’s oddly altered by the lack of sweetness.

  All in a
ll, I think Beauchamp might be right. If I had to pick one flavor sense to lose, I’d probably rather give up smell and keep taste. Food that lacks the basic tastes is not actively bad or repugnant, just utterly unfoodlike. If every meal was like this, I’d certainly have a hard time sitting down to eat three times a day.

  You’d think that such a vital sensory system—especially one that’s relatively simple, with only a handful of basic tastes—would be completely understood by now. Not so: Huge gaps remain in our understanding of how taste works. Scientists can’t even agree on how many basic tastes there are.

  At the simplest level, we know a fair bit about some parts of the story. Tasting happens when the thing we taste—the tastant—binds to receptors on taste cells on the tongue or palate. The tastants for salty and sour—sodium and acids, respectively—go right into the taste cells and activate them, in a process that’s still not fully understood. The process is pretty well worked out for sweet, umami, and bitter, though, so let’s look at them in a little more detail.