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by Tom Vanderbilt

  Back at the Warfighter Café, I contemplated the spread before me. How did the MREs of tomorrow stand up? Did they still deserve the unfortunate sobriquets such as “meals refusing to exit” or “meals rejected by Ethiopians”? I took a bite of “MATS Salmon,” “MATS” standing for “microwave-assisted thermal sterilization.” The name could use a little work and the fish was, admittedly, a bit tough. “It’s a little chewier than we’d like,” Darsch told me. Not surprisingly: The salmon had been bombarded with over 120,000 psi of pressure, literally rupturing the cell walls of any lingering bacteria with the ruthlessness of a bunker-busting bomb. But the taste was there, at least more than one would expect for a shrink-wrapped piece of room-temperature fish with no immediate sell-by date. Would it fly at Del Posto? No. But to a soldier faced with a long-range patrol in a hot desert, it might be just good enough.

  I MAY KNOW WHAT I LIKE, BUT I KNOW I DON’T LIKE WHAT I DON’T KNOW: LIKING IS LEARNING

  On the morning I went to Philadelphia to meet Marcia Pelchat, a longtime researcher at Monell, I was nursing a slight cold. When I arrived at her office, Pelchat, a petite, polite woman with a disarming sense of humor, offered me coffee. I asked if she had tea, explaining that whenever I have a cold, I prefer tea, which suddenly seems to taste better than coffee. She considered it for a moment, then said, “Coffee without the aroma would seem like ashes to me.”

  Here is that thing that is so easy to forget yet never fails to startle when we experience it firsthand: Most of the action when we are tasting something comes from the nose. Coffee is one of those curious things that smells better than it tastes, and to lose the smell of it is in essence to lose what we like about it. To remind yourself of this basic sensory fact, it is worth, every once in a while, administering to yourself what Pelchat does to me on this morning: the jelly-bean test. She handed me three jelly beans and asked me to hold my already stuffed nose. They each tasted, simply, sweet. When I released my nostrils on the last jelly bean, I suddenly experienced, even with my cold, a spreading flood of flavor, something like Häagen-Dazs coffee ice cream, through the back of my mouth and nose. I had, in fact, just eaten a coffee-flavored jelly bean, as well as its banana- and licorice-flavored cousins.

  Our taste-bud-studded tongues do the basic sensory sorting: sweet, sour, bitter, salty, and, less officially, umami (and maybe fat). But all the finer distinctions—mango versus papaya, lamb versus pork—come “retronasally,” from the mouth up through the nasal passage, as a smell. The things we know as strawberries or Coca-Cola or sriracha sauce are not tastes; they are flavors. There is, strictly speaking, no “taste of honey”; there is “retronasal olfaction of honey.” Honey, to be honey, needs to waft on a gust of inhaled air into our nasopharynx. Even seemingly strong “tastes,” like lemon, only read on the tongue as a collection of sours and bitters and sweets. Terpenes triggering receptors in the olfactory mucosa make lemon lemony.

  How we perceive something, Paul Rozin has argued, influences how we feel about it. Even people who do not like the taste of coffee can no doubt appreciate the aroma. By contrast, on a plate, Limburger cheese may strike us, via our nose, as unpleasant. Once in the mouth, however, it undergoes a stunning change into something we may find pleasurable. It is as if the brain, sensing that food is in the mouth, and thus no longer represents some external hazard, shifts its whole outlook. Give someone who has a nose-blocking cold a cup of beef broth to which yellow food coloring has been added, Pelchat told me, and he will think he is eating chicken soup. Take away the retronasal passage, and it would be like going from a cable television package with an almost infinite number of channels down to a handful of networks playing the same old shows.

  But I have come to Pelchat’s office to talk about liking. Regardless of which part of my mouth and nasal cavities are telling me what the flavor is, what is telling me I like it? Virginia Woolf once wrote that “reading is a longer and more complicated process than seeing.” So too is the question of whether we like something more than feeling a sensory response to something we have put in our mouths. What we like is sometimes corrupted by what we know we like. A study that had consumers test pineapple varieties found those who preferred pineapples labeled “organic” and “free trade” tended to be those who were more fond of organic and free trade produce itself. Those less keen on organics were less happy about the pineapple. As the researchers noted, “The same cognitive information evoked opposite affective reactions in different subjects.”

  Pelchat, it turned out, did have some tea for me. But first she wanted me to take a capsule, which would contain either sugar or, simply, non-caloric cellulose. She wanted to show me the taste mechanism known as “flavor-nutrient” conditioning—the idea that we like what makes us feel good, even if we do not know it.

  The power of this conditioning has been shown in any number of studies on rats, our fellow neophobic omnivores. Typically, a rat will drink, ad libitum (as much as it wants), something like orange Kool-Aid. Rats, as a cursory glance at the scientific literature reveals, drink a lot of Kool-Aid. Meanwhile, sometime before, during, or after, a sweetener will be “infused,” via “intragastric catheter,” directly to its stomach. Later, the rat will sample grape Kool-Aid without getting the sugar drip to the stomach. When both flavors are later tested, rats will prefer the one that was sweetened, even when both flavors are now unsweetened. Sometimes they still cling to the old favorite when one of the new options actually tastes sweet in the moment.

  Curiously, the way the rat came to like one flavor over another had nothing to do with a taste preference. How do researchers know? “In fact,” Pelchat tells me, her voice lowering a bit, “the esophagus is externalized.” With the gullet sitting outside its body, the rat cannot taste the glucose, nor could he belch it back up into his mouth. Infused into the stomach, however, that sweetness still provides a hedonic payoff. “Something in the gut or the metabolic system is making them like that flavor,” Pelchat said.

  Pelchat wondered if humans’ sensory mechanisms could be similarly bypassed, without such extreme surgery. So she once swallowed a nasogastric tube for a day and tried to mainline glucose. “I thought, I know what I’m doing, I’ll pretend it’s food and I’ll swallow it, it’ll be fine. Instead, I was puking, tearing up.” Finally, she hit upon pills, which would or would not release sweetness into the gut. A placebo cellulose pill has no calories, no benefit for the body. Well, almost no benefit. “Incidentally,” she noted with a laugh as I inspected a pill, “that will keep you regular.” In her study, people who downed the (tasteless) sugar pills ended up liking the flavor of tea more than the tea they drank with the unsweetened pills.

  So without even knowing why, people preferred one tea over another (we are strangers to our taste). They were getting “post-ingestive” signals, in the form of a nutritional reward, that predisposed them toward a flavor. “I always make a point of telling people that reward and pleasure are not the same thing,” she says. “Food can be rewarding without the conscious experience of pleasure.” How we have all known this, eating in front of the television. The reverse can happen as well. Cancer patients who sampled a novel ice cream flavor prior to chemotherapy, with its attendant nausea, grew to dislike that flavor (more than the familiar flavors they liked). With liking for all foods diminished, patients were in little mood for novelty. One way to avoid the treatment from negatively interfering with normal appetites, interestingly, was to provide a new “scapegoat” flavor—like Life Savers candy—during patients’ normal meals. The scapegoat flavor, rather than the usual foods, absorbed the brunt of disliking. This plays into our tendency to want to like familiar foods and to dislike the novel.

  In Pelchat’s study, sponsored by a tea company wanting to see if Americans could acquire a taste for unsweetened teas, people even grew to like the tea more that did not have the glucose hit. Why? Simply because they were drinking it more than once. In 1968, the psychologist Robert B. Zajonc, in a profoundly influential paper, termed wha
t he called the “mere exposure” effect: “Mere repeated exposure of the individual to a stimulus is sufficient condition for the enhancement of his attitude toward it.” He was not actually talking about food, but exposure has come to be a central idea in food liking. In one typical study, children as young as two sampled a collection of unfamiliar fruits and cheeses for twenty-six days in a row. When they were later given a choice between random pairs of the food objects they had tried, they chose the ones they had had more often—even when they had spat those out initially.

  Try it, the old Alka-Seltzer ad (cheekily) promised, you’ll like it. Parents do not usually have the patience of researchers (nor can they resort to gastric tubes). They often abandon efforts to give their children new foods after three or four tries. In an English study, one group was asked to repeatedly eat spinach, not a huge delicacy in England. Another group was asked to eat peas, which are more liked. People began to like spinach a bit more, particularly those who disliked it at first. But liking for peas started high and stayed high. People liked peas because they were already used to liking peas.

  Exposure speaks to the idea that we like what we know. But to know it means we first have to eat it, even if we dislike it. In one study, people began to like an initially disliked low-salt soup after having it just a few times (the soup was not labeled “low salt,” because this in itself could be enough to negatively sway liking). In another experiment, people ate canned ratatouille servings with successively higher levels of chili added. The hotter the burn, the more they grew to like it. George Orwell, in his 1946 essay “A Nice Cup of Tea,” predicted this kind of taste adaptation: “Some people would answer that they don’t like tea in itself, that they only drink it in order to be warmed and stimulated, and they need sugar to take the taste away. To those misguided people I would say: Try drinking tea without sugar for, say, a fortnight and it is very unlikely that you will ever want to ruin your tea by sweetening it again.”

  Liking is learning: This truism runs from entire cultures down to the individual. The exposure effects begin even before we are born. Like carrot juice as an infant? Chances are your mother did. The odors and tastes were all around you, in the atmosphere of amniotic fluid that was your earliest dining experience. Trained sensory panelists can even tell which women have consumed garlic pills based on the scent of their amniotic fluid alone. Out of the womb, we strain toward the things we prefer (that is, the familiar) and make “aversive gapes” at the things we dislike. Making faces is part of the social experience of liking and, especially, disliking: We send cues about what we are eating and look for information about what others are eating.

  Simply seeing other people eating something seems to promote liking. In a classic study looking at the feeding of children in a women’s prison in the 1930s, children’s preferences seemed to be informed by whoever was feeding them: “Babies who refused tomato juice were found to be fed by adults who also expressed a dislike for tomato juice.” In a study of preschoolers, a “target” child who preferred one vegetable to another was seated with three classmates who had the opposite preference. By the second day of the study, the target child had already switched preferences. Exposure to people, as much as food itself, influences our liking.

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  Mysteries still abound in our liking for food. Consider the simple question of why we should suddenly like something that we previously disliked. Very few of us “like” a substance like coffee or beer the first time we drink it, but many of us come to like it. All tastes are, in essence, “acquired tastes.” Or, as Pelchat suggests, “an acquired liking is really what we should say.”

  And when we talk about “acquired tastes,” we should really be talking about “acquired flavors,” as Dana Small, an associate fellow in Yale University’s John B. Pierce Laboratory who studies the neuropsychology of eating, suggested to me. We are not born knowing about flavors like coffee; we simply know the drink as bitter and thus bad. “The bitter is there as a sign that there is a potential toxin in whatever you’re sampling,” she said. “You just want to know that; you don’t want to have to learn that.”

  But no one is born liking, or not liking, chicken feet. Those “gatekeeper” taste systems, after all, would not likely know feet from wing. It is all chicken. Before food even gets to us, culture has done that first big sort, sifting out the boundaries of what is acceptable to like. “The French eat horses and frogs but the British eat neither,” notes Jared Diamond. As with any food, the French, during a discrete historical moment, had to be taught to “learn to like” horse as food. But what we like in taste, as opposed to flavor, is remarkably similar around the world. As John Prescott writes in Taste Matters, “The sweet taste of sucrose in water, is optimally pleasant at around 10–12 percent by weight (approximately the same as is found in many ripe fruits), regardless of whether you are from Japan, Taiwan, or Australia.”

  Flavor conditioning helps us to like or dislike flavors. The benefit of this is, as Small put it, that we can “learn to like the foods that are available to us, and avoid particular foods rather than entire classes of nutrients.” When she was young, she went to a popular sailing event in her hometown of Victoria, British Columbia. With college friends, she partook of one too many drinks of Malibu and 7UP, an unholy and intensely cloying concoction of sweet, coconut-flavored rum and citrusy soda pop. “That was twenty years ago,” she recalled. “I can’t even wear coconut suntan lotion. It makes me ill.”

  Through a complex chain of activity in the brain, she said, we learn “flavor objects”—the “perceptual gestalt” of touch, taste, and smell in everything we eat. “Did this food make me sick? Did this food give me energy? You learn preferences based on the entire flavor object.” The flavor object itself is “created” by a network of neural activity, described as “a distributed circuit including the neural representation of the odor object, unimodal taste cells, unimodal oral somatosensory cells, multimodal cells, and a ‘binding mechanism.’ ” You do not just “taste” a strawberry; you virtually conjure it into being.

  Coffee—the actual substance—becomes no less bitter the hundredth time we drink it than the first time we drank it. But something happens. “It becomes coffee,” Small said. “The brain has learned that coffee is not a potentially harmful signal.” Many of us, when first drinking coffee, add things that we like—milk and sugar. This not only weakens the bitterness but helps build positive associations with the coffee. The relationship is one-way, notes John Prescott: We do not learn to like sugar by drinking coffee; we learn to like coffee by drinking it with sugar. Add the post-ingestive signal of caffeine, and you have got a drink that we like, almost as if in spite of ourselves. You may be thinking the pleasures of caffeine or alcohol are enough to explain why we become conditioned to liking coffee or whiskey. But then why not just add those substances to what we already like? Why is it the things that are most disliked in the beginning go on to be the things we like the most?

  There must be a moment when our disliking actually shifts to liking. Small has been trying to locate it in neurologic time and space. In one experiment, she had subjects try novel-flavored beverages that had no calories. After a few weeks, she added caloric but tasteless maltodextrin to one of the flavors. Even though they could not sense its presence, subjects liked the beverages with maltodextrin more. As with Pelchat’s tea study, the “post-oral signal” coming from the gut—which is happily converting the maltodextrin into glucose—changed liking.

  In Small’s study, though, the beverages were all chosen to be “slightly liked.” This still does not answer how we get from disliking to liking. What if you could take a food that is intensely disliked and, in the flick of a switch, suddenly generate an intense desire? Kent Berridge, a neuroscientist at the University of Michigan, did just that in a Pavlovian conditioning experiment with rats. First, rats got “pulses” of a pleasant sucrose solution, along with a sound. They also got a deeply unpleasant, three-times-as-strong-as-seawater solution of
“Dead Sea salt,” accompanied by a different sound.

  The rats hated the salt—so much so that it had to be delivered into their mouths via an “implanted cannula.” And when the rats subsequently heard the respective tones, they turned either away or toward the food source and made the appropriate facial expression. Next, the rats’ brains were altered with injections that triggered a kind of simulated extreme salt craving. The following day, when the rats were again presented with the tones, they immediately moved toward the Dead Sea salt, making vigorous lip-licking “pleasure” faces (the same as seen in human infants)—before they had even tasted it in its new, “pleasant” state. In other words, without even knowing that they liked it, they suddenly wanted it.

  This might help explain not just addictive behaviors but everyday liking. In one study, Berridge and colleagues asked student subjects to identify the gender of faces seen on a computer screen. They were also shown, rather surreptitiously—at one-sixtieth of a second—angry or sad faces. Afterward, they were given a fruit beverage, which they were told was in development by a soft-drink company, and asked how much they liked it. Subjects who saw the “happy” faces reported liking the drink 50 percent more than subjects who saw the sad faces. The happy faces triggered “mesolimbic circuits of ‘wanting’ in the brains of students who viewed them, which persisted for some minutes undetected as students evaluated their own mood,” Berridge wrote. “The ‘wanting’ surfaced only when an appropriate target was finally presented in the form of a hedonically laden sweet stimulus they could taste and choose to ingest or not.” It was as if they were, to paraphrase the old country song, “looking for like in all the wrong places,” finally finding something in which to express their interest.