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  Leo Tolstoy famously wrote that happy families are all alike, while each unhappy family is unhappy in its own way. Taste is kind of like that, too. The good tastes, umami and sweet, are each recognized by a single receptor, a two-part protein that’s woven into the outer membrane of taste cells. (There may be other, unrelated receptor molecules that are also sensitive to sweet and umami tastes, but the evidence there isn’t conclusive yet.) For umami, the two parts are called T1R1 and T1R3, while for sweet it’s T1R2 and T1R3. The amino acid glutamate, or one of several sugars, slip into fitted pockets on these combo receptors. The traditional metaphor here is a key fitting into a lock, but you could also think of the way an expensive camera slots into a foam carrying case. If you have the wrong case for the camera, it doesn’t fit. If they match, the camera slips in perfectly.

  The bad, bitter taste, on the other hand, makes use of a huge committee of receptors called T2R receptors. Each member of the committee—there are at least twenty-five in humans—handles a different range of bitter compounds. Some, like T2R10, T2R14, and T2R46, are what the scientists like to call “promiscuous,” mating with a wide range of bitter compounds. In fact, if you just had those three T2Rs and no others, you’d be able to detect more than half of a test sample of 104 diverse bitter-tasting chemicals. Some other bitter receptors, like T2R3, seem to be monogamous, with only a single chemical known to activate them. It works the other way, too: Some chemicals activate many different T2Rs, while other chemicals trigger just a single bitter receptor. What’s more, bitter receptors seem to come and go over the course of evolution: The human genome is littered with the rusting hulks of bitter receptor genes that no longer function. These must have been important in our evolutionary past, but—like the sweet receptors of cats—they have become irrelevant enough that we no longer need them, and we haven’t noticed their absence.

  Scientists still don’t know whether all those bitter receptors send identical signals to the brain—in which case there’s just a single taste we call “bitter”—or whether we can actually taste the difference among different classes of bitter. Part of the problem is that when you compare, say, the bitter of a hoppy ale to that of coffee, you’re not just comparing the output of particular bitter receptors, particularly T2R1 for hops and T2R7 for caffeine. Instead, you’re really comparing the whole flavor profile of the two drinks. Even if you hold your nose while drinking—which few of us do in a social setting—the two differ in other tastes such as sweet and sour. We don’t generally experience, let alone compare, pure bitter tastes in our everyday lives. But research scientists do, and at least one expert is convinced that there’s more than one bitter taste. “When you do a lot of bitter research, and taste these things side by side, you realize they taste different,” says John Hayes, a flavor researcher at Penn State University. And that plays out in our food preferences, he thinks. “I like my beers very hoppy,” he continues. “I love a good IPA. And yet I can’t stand grapefruit, because I find it bitter. If there was only one kind of bitterness, then the learning process that I went through to learn to like my IPAs presumably would have generalized over to grapefruit juice. And the fact that it hasn’t generalized, to me, starts to provide some of the argument for why there’s more than one kind of bitterness.” He’s now hard at work in his lab trying to prove this hunch.

  There’s a lot left to learn about umami, too. Now that scientists have found the receptor responsible for umami, there’s little doubt that it deserves to be considered the fifth basic taste. But for most people, it’s still a little hard to accept. After all, everyone knows exactly what you mean when you talk about sweet, salty, sour, or bitter. If umami is just as fundamental a taste, then why does it so often need to be explained? What makes umami so obscure?

  Two reasons, says taste researcher Paul Breslin of Monell. First, we routinely experience the other tastes in nearly pure form: the sweetness of honey, the sourness of lemon juice, the bitterness of radicchio, a pinch of salt. “You get, like, a pure shot of those,” he says. “But you’re never going to experience pure glutamate in the world. You’re not going to find a pile of it that you can lick. We really only experience it in combination with a lot of other things.”

  That inability to isolate the taste of umami is reinforced by Breslin’s second reason: Our umami receptors max out at low intensity, so we’re physically unable to experience very umami in the same way we can taste very salty or very bitter simply by piling on the salt or brewing a cup of extra-strong espresso. Thanks to our perceptual apparatus, umami can never be anything more than a subtle sensation. It’s as though you could understand the color red from referring to a crimson rose, yellow from a lemon, and green from a midsummer forest, but then had to try to figure out blue from skim milk.

  There’s also a cultural component to our umami blindness, however. Most people from Western countries struggle to put a name to umami taste sensations, but that’s not the case for people from Asian countries. “If you look at Japanese kids, you put MSG in their mouth and they say ‘umami’ like that,” says Danielle Reed, Breslin’s colleague at Monell, with a snap of her fingers, “like American kids put sugar in their mouth and say ‘sweet.’” As umami becomes a more prominent part of our food culture—with food writers tossing the term around freely now, and restaurants like Umami Burger part of the general conversation—it’s likely that our umami blindness will gradually recede into the past.

  When that happens, it will be interesting to see whether our appreciation of umami rescues the reputation of MSG. MSG—monosodium glutamate—is, after all, merely sodium, which is pure salty taste, and glutamate, which is pure umami taste. When chefs work hard to enhance umami by adding dashi or soy sauce to stocks, incorporating mushrooms in stews, aging their meat, or incorporating fermented ingredients, they are simply boosting the glutamate content of the finished dish—and we love the result. Why, then, do so many of us shudder at the thought of boosting glutamate directly, by adding it in pure form? We routinely see signs in restaurant windows or labels on packaged foods proclaiming “No MSG!” But what self-respecting cook would ever boast of doing without salt, sugar, or lemon juice?

  The reason for MSG’s bad reputation, of course, is that many people feel that it causes an unpleasant reaction when they eat food that has had MSG added. This notion, which is now commonplace, is actually a relatively new idea. It first appeared in 1968 when a Chinese American doctor, Robert Ho Man Kwok, published a letter in a leading medical journal describing “numbness at the back of the neck, gradually radiating to both arms and the back, general weakness and palpitation” beginning a few minutes after starting a meal at a Chinese restaurant. Kwok wasn’t sure what caused this “Chinese restaurant syndrome,” but he suggested MSG as one possibility.

  The news media quickly picked up the story, and similar anecdotes began popping up all over. Soon researchers began giving MSG to volunteers, who reported symptoms similar to Kwok’s syndrome and added others, such as headache, to the list. The idea that MSG could be bad for you became widespread. Soon Ralph Nader and others were urging governments to regulate its use.

  But even then, skeptics wondered: If MSG really produces such unpleasant symptoms, why didn’t anyone notice this sooner? After all, the food industry had been using MSG for decades, and not just in Chinese food. By the time Kwok published his letter, the United States alone produced fifty-eight million pounds of MSG every year, and it showed up in everything from baby food to canned soup to TV dinners. Yet no one had remarked on a “TV dinner syndrome” or “canned soup syndrome.”

  All this made MSG research a hot topic during the 1970s. As scientists dug deeper into the compound’s effects, though, Chinese restaurant syndrome began to look more and more iffy. The most damning evidence came from several studies of people who claimed to be sensitive to MSG. Researchers gave all the volunteers a capsule to swallow, without telling them whether it was MSG or a dummy capsule containing inert ingredients. (Using a swallowable cap
sule prevented the volunteers from tasting the difference.) If there was any truth to their self-professed sensitivity, participants should have developed symptoms of Chinese restaurant syndrome when they consumed MSG, but not when they took the placebo. In fact, though, the volunteers reported just as many symptoms with the placebo as with MSG—strong evidence that their symptoms stemmed from what they expected to happen, rather than from what they actually ate.

  That’s not as surprising as it sounds. Most of us have felt a little funny after eating now and then. Maybe you ate a bit too much, or too fast, or were feeling tense for other reasons. And many of us are especially cautious after eating something new, as Chinese food would have been for many people in the 1960s. Once one unsettling experience has planted a seed of doubt, our expectations can start to turn our future responses into a self-fulfilling prophecy.

  In fact, when researchers looked back at the early studies that first suggested a link between MSG and Chinese restaurant syndrome, most of them suffered from this expectation problem. Usually, the researchers had not bothered to hide the taste of MSG, so that participants in the study could probably guess whether they’d consumed MSG or a placebo. Some studies didn’t even attempt a placebo but simply gave MSG to people and asked them if they felt any symptoms—an ideal situation for expectations to take the driver’s seat.

  Even so, there are no doubt a few people out there with a genuine sensitivity to MSG. But if pure MSG causes problems, those people should also have trouble with dishes containing mushrooms, soy sauce, Parmesan cheese, and other foods naturally rich in umami flavor. And of course, overuse of MSG could bring its own problems, just like overuse of salt or lemon juice or any other seasoning. With those cautions in mind, though, there’s no reason why most cooks shouldn’t incorporate MSG into their repertoire of seasonings. After all, most kitchens have recourse to pure chemical seasonings to boost the tastes of salt (sodium chloride), sweet (sucrose), and sour (acetic acid, aka vinegar). Why not keep a little MSG on hand for those times when a dish needs a boost of pure umami?

  When it comes to industrial taste research, though, umami is small potatoes. The big money is in sweet. Like umami, sweetness is all about a single taste receptor, as far as we know (although, as we’ll see in a moment, there may be some reason to suspect other receptors, too). And that simplicity has sparked a huge effort from scientists—mostly working for Big Food—to find alternative ways to tickle that receptor that aren’t accompanied by the caloric charge of real sugar.

  Most of the artificial sweeteners already on the market are the result of pure dumb luck. The oldest was discovered by accident in 1878 when Constantin Fahlberg, a chemist working on coal tar products in Baltimore, forgot to wash his hands before supper and noticed that his bread tasted “unspeakably sweet.” He thought nothing of it until he noticed the same sweetness on his napkin, his water glass, and, eventually, his thumb. Fascinated, Fahlberg dashed back to the lab and started tasting everything he could find. Fortunately, he found the sweet compound, which we now know as saccharin, before he got to anything too toxic.

  Cyclamate has much the same story: in 1937, a chemist at the University of Illinois set his cigarette down on the corner of his lab bench and noticed when he picked it up again that it tasted sweet. Aspartame: a chemist working on antiulcer drugs in 1965 licked his finger to help pick up a piece of paper and noticed a sweet taste. Sucralose: a chemist in London was asked by his boss in 1976 to “test” a new chemical, but misheard it as “taste”—a potentially lethal error for a chemist, but one that worked out well for the company.

  Artificial sweeteners reduce calories for two reasons. Some, such as saccharin and sucralose, are not broken down by the body and thus provide no calories. Others, such as aspartame, taste sweet at lower concentrations than regular sugar, so even though they are digestible, they deliver their sweetness with fewer calories. There’s a catch—even though some of these chemicals start tasting sweet at low concentrations, their sweetness often maxes out early, too. No matter how much saccharin you dump in your coffee, for example, it never tastes sweeter than a 10.1 percent sugar solution. That’s a problem for soft drink manufacturers, because regular Coke is 10.4 percent sugar, and Pepsi is about 11 percent.

  That’s not the only reason artificially sweetened drinks taste a little weird to many people. Another is that most of the artificial sweeteners trigger not just the sweet receptor but also one of our many bitter receptors, producing a bitter aftertaste that many people find highly objectionable. Since people have different sets of bitter receptors, some of us are bothered by certain sweeteners and not others. I get a bitter taste from saccharin, for example, which suggests that my T2R31 bitter receptor works well. On the other hand, I get no bitter taste from the low-calorie natural sweetener stevia, so I probably have a broken version of whichever bitter receptor (still unknown) responds to that sweetener.

  But bitterness isn’t the only problem with the taste of artificial sweeteners. Linda Bartoshuk, for example, can’t taste the bitterness of aspartame or saccharin, yet she knows them when she tastes them. “The sweet of saccharin is nothing like the sweet of sucrose. I don’t know how anybody could ever confuse them,” she says. “And if I accidentally get a beverage with aspartame in it, I’m not confused for a moment. I don’t like it. So it’s pretty clear that not all sweets are the same.”

  Part of the reason for that is that each sweetener has its own distinctive timing for triggering the sweet receptor. Real sugar reaches its peak sweetness in about four seconds, then the taste trails off about ten seconds later. Most artificial sweeteners hang on too long, producing a cloying aftertaste. Aspartame, for example, starts a second later and lasts four seconds longer. But Bartoshuk thinks the taste differences might also point to the existence of a second kind of sweet receptor, as yet unknown. It’s hard to believe that we don’t know everything yet about something as obvious—and as lucrative for Big Food companies—as sweetness, but there you are.

  If artificial sweeteners are the king of taste research, dollar-wise, then salt substitutes would have to be the queen. The average American consumes about 9 grams of salt daily, almost half again as much as the recommended maximum of 5.8 grams per day, and the majority of that comes from processed foods. That high salt intake is a big reason why sixty-five million American adults have high blood pressure. As a result, food-processing companies are under a lot of pressure to find ways of reducing the sodium in their products.

  The problem is, that’s not easy to do. As anyone who’s spent time in a kitchen knows, salt contributes much more than just a salty taste to the flavor of a dish. Used judiciously, salt can enhance all the other flavors, making meat meatier, beans beanier, and potatoes potatoier. That’s largely because the sodium ions help draw other flavor compounds—mostly components that enhance smell, not taste—out of the ingredients and into solution, where we can detect them. Omit the salt, and your food literally has less flavor. This explains why a skilled cook can often tell by smell whether a dish needs more salt.

  To find out how food scientists are working around the problem, I asked Peter de Kok, who works for the food science company NIZO in the Netherlands. De Kok—who, like most Dutch scientists, speaks flawless English—comes across as a cheerful fellow with a boundless enthusiasm for salt reduction. There are three ways to deliver all the flavor bang of regular salt with less sodium, he says. You already know about the first one if you’ve ever bought “low-sodium salt” in the grocery store: simply replace some or all of the sodium with another salt ion. The more chemically similar your replacement is to sodium, the better job it does of substituting. In practice, that pretty much restricts the choice to potassium, which is about 60 percent as salty as sodium. (Lithium would actually be a better substitute, flavor-wise, but it has powerful psychological effects—just ask anyone with bipolar disorder.) Unfortunately, many people—though I’m not one of them—also get a bitter taste from potassium, so companies can only swap out
part of the sodium in their low-sodium salt.

  If you don’t want to replace sodium with a different ion, a second approach is to find a way to get more flavor from the same amount of salt. Smaller salt crystals dissolve more quickly, so they taste saltier when sprinkled atop food. (The converse is also true, of course—when you eat a pretzel topped with the traditional big salt grains, you’re actually getting more sodium than necessary for the amount of salty flavor it delivers.) De Kok and his colleagues also try to find ways of getting more of a food’s sodium out of the food and into your mouth, where you can taste it. For example, they’ve been working on changing the texture of sausages to make them juicier. In essence, he says, when you chew these juicier sausages you squeeze more of the salty moisture out into your mouth, so the sausages taste just as salty with 15 percent less salt. Yet another strategy exploits the value of contrast: They’ve patented a method of making bread with alternating layers of salted and unsalted dough. As you bite through the layers, the contrast makes the salty parts stand out, so that the whole bread tastes about 30 percent saltier than it otherwise would.

  The third way to cut back on salt without reducing flavor is a bit more devious: Trick the brain into thinking the food is saltier than it is. As we’ll see, your brain blends aromas and tastes together into a unified perception of flavor. Knowing this, de Kok and his team have been experimenting with adding aromas that we’re used to smelling in high-salt contexts. Because anchovies are typically salty, for example, you mentally “add salt” whenever you get a whiff of anchovies, whether the salt is really there or not. You can’t flavor everything with anchovies, though, so de Kok found an alternative that’s more universally beloved but still salty: bacon. The researchers isolated about two dozen different aroma compounds from bacon, then tested each one to see if it enhanced people’s perception of saltiness. Sure enough, they found three that did. By selecting meat that’s naturally high in those three compounds, de Kok’s team was able to make sausages that still tasted right but used 25 percent less salt.