Flavor Read online

  FLAVOR

  The Science of Our Most Neglected Sense

  BOB HOLMES

  W. W. NORTON & COMPANY

  Independent Publishers Since 1923

  New York | London

  For Deb, my partner

  in flavor and in life

  CONTENTS

  Introduction

  Chapter 1. BROCCOLI AND TONIC

  Chapter 2. BEER FROM THE BOTTLE

  Chapter 3. THE PURSUIT OF PAIN

  Chapter 4. THIS IS YOUR BRAIN ON WINE

  Chapter 5. FEEDING YOUR HUNGER

  Chapter 6. WHY NOT IGUANA?

  Chapter 7. THE KILLER TOMATO

  Chapter 8. THE CAULIFLOWER BLOODY MARY AND OTHER CHEFLY INSPIRATIONS

  Epilogue: THE FUTURE OF FLAVOR

  Acknowledgments

  Notes

  Index

  FLAVOR

  INTRODUCTION

  Have you ever wondered why beer and salted peanuts go so well together? Scientists know the answer: Salty tastes inhibit bitter ones, so the nuts tame the beer’s bite and allow some of its other flavors to step forward. Once you know this principle, you can apply it in many other ways. Serve the nuts (or pretzels) with gin and tonic. Add a little extra salt if tonight’s broccoli is especially bitter. Put a pinch of salt on your morning grapefruit.

  The science of flavor is full of insights like that, but hardly anyone knows about them. That’s because flavor barely registers in the screenplay of our daily lives. We rarely examine the flavors we experience, and as a result we don’t know how to talk about them or think about them. Here’s a thought experiment to prove it: Take a moment and bring to mind one of your favorite pieces of music. Recall how it’s put together and what makes it special for you. Is it the subtle use of the saxophone in the bridge section? The way the first violin and cello trade the theme back and forth? The moment of breath-holding suspense just before the vocals start? Chances are, you can put your finger on several specific elements that make that music sing for you. You can name the instruments that are playing, you can pick out the melody, bass line, and vocals, you know how fast the beat is.

  Now try to describe your favorite apple variety in the same detail. Why do you like, say, Fujis better than any other? Most likely, you’ll stammer out a few generalities about crispness or sweetness or “more flavor.” But unless you’re a trained apple taster (and such people do exist), you probably won’t be able to manage much more than that. You certainly won’t be able to name the apple’s flavor elements as nimbly as you named the instruments in your favorite music, and you probably won’t have much to say about how the flavor profile of each bite builds and ebbs.

  And our imprecision is not confined to just apples. Can you describe how the flavor of halibut differs from red snapper? Or how Brie cheese differs from Cheddar? The fact is that for most of us, flavor remains a vague, undeveloped concept. We say “dinner tasted good,” or “I like those peaches,” but we never dip beneath the surface of those superficial responses. It’s not that we’re blind to flavor. If you can recognize that a Fuji apple differs from a Spartan, or that Brie differs from Cheddar—and almost all of us can—you have the basic perceptual tools to explore the world of flavor in greater depth.

  What holds most of us back is that although we experience flavor every day, we just don’t know much about it. We sip our morning coffee or enjoy our dinner while largely ignorant of the complex interplay of taste, smell, touch, sight, and even expectation that creates the sensation we know as flavor. Without that knowledge, we lack the means to describe what we experience, and as a result, far too often we simply don’t notice the fine details of what we eat and drink. It’s as though the entire world of flavor has been relegated to the background—elevator music for the palate, as it were.

  Sometimes that’s fine, of course. Sometimes all we really want is background music, or a quick bite to eat without bothering too much about the details. But in our musical world, most of us take that extra step now and then. We pay attention and dig a little deeper, and our lives are much richer for it. We can have the same rich experience in our flavor lives, too—but only if we learn more about the world of flavor: how we perceive flavor, where it comes from, and how we can maximize it, both on the farm and in our kitchens. That’s where this book can help.

  Paying attention to flavor makes life not just richer but deeper, because flavor appreciation may be a uniquely human gift. The biology of our species—the fact that we live in social groups, inhabit essentially every environment on Earth, and eat a diverse, omnivorous diet—means that our ancestors had to become very good at certain skills. They had to recognize faces to tell friend from foe, neighbor from relative, and honest dealer from cheater. As a result, all of us, with a few rare, pathological exceptions, are indeed skilled at picking out the subtle differences that distinguish one face from the next. We recognize, and often remember, the face of someone we went to school with years ago, and the stranger we met casually at a party yesterday. And we do it instantaneously, at a glance, not by laboriously piecing together evidence from nose, ears, cheekbones, and eyes. This recognition skill is special and unique to faces. It’s not just a consequence of sharp perception and attention to detail—we have nowhere near the same ability to recognize people by their hands, for example.

  Flavor recognition is another of humans’ special skills. As omnivores, our ancestors had to judge what they could eat and what they couldn’t, and flavor is how they made that decision. Those skills are now part of our evolutionary heritage. “All humans are flavor experts in the same sense that we’re face experts,” says Paul Breslin, a leading psychologist who studies flavor perception. “It is literally a life-or-death matter. If you eat the wrong things, you’re dead.” We recognize the flavor of a strawberry or a pineapple or a green bean in a flash, even if we can’t put a name to it without prompting.

  In fact, our flavor sense may have played a large role in making humans into the species we are. Anthropologist Richard Wrangham argues that we could never have evolved our huge, expensive brains without the easy calories made available by cooking. Raw foods simply don’t yield enough calories to get our modern, big-brained bodies through the day. Our cousins the chimps spend hours each day laboriously chewing their raw foods to extract the calories—time and energy that humans can put to better use. And people who follow a raw-food diet typically lose significant weight, even with blenders and juicers to take the place of constant chewing. Cooking breaks down indigestible tissues into smaller, more digestible fragments, and thus helps us get more from our meals for less effort. And in the process, it creates a whole host of delicious new flavors.

  We are also the only species that seasons its food, deliberately altering it with the highly flavored plant parts we call herbs and spices. It’s quite possible that our taste for spices has an evolutionary root, too. Many spices have antibacterial properties—in fact, common seasonings such as garlic, onion, and oregano inhibit the growth of almost every bacterium tested. And the cultures that make the heaviest use of spices—think of the garlic and black pepper of Thai food, the ginger and coriander of India, the chili peppers of Mexico—come from warmer climates, where bacterial spoilage is a bigger issue. In contrast, the most lightly spiced cuisines—those of Scandinavia and northern Europe—hail from cooler climates. Once again, our uniquely human attention to flavor, in this case the flavor of spices, turns out to have arisen as a matter of life and death.

  Our unusual anatomy cooperates in making humans connoisseurs of flavor. Our upright posture and oddly shaped head (compared with other mammals) helps our noses focus less on smells coming from the outside world and more on the flavors wafting up from the food in our mouths. And flavor engages a disproportionate share of our big, power
ful brains. When you enjoy a delicious piece of cheese, or a glass of wine, or a cookie, you’re engaging more brain systems than for any other behavior. Flavor taps into sensory systems for taste, smell, texture, sound, and sight. It involves motor systems for coordinating the muscles that allow you to chew and swallow. It activates the unconscious linkages that regulate appetite, hunger, and satiety. And, not least, it fires up the higher-level thought processes that help you identify, evaluate, remember, and react to what you’re eating. That’s a big bundle of brain activity from a simple bite of food.

  Flavor pulls on our brains in subtle but powerful ways. When odor information—the most important component of flavor—enters the brain, it goes directly to the ancient parts of the brain responsible for emotion and memory. It doesn’t reach the conscious, logical part of the cerebral cortex until several stops later. That’s the neuroscientific basis for flavor’s remarkable ability to move us: A taste of a favorite food can transport us back to our childhood more powerfully than a song or a photo ever could. It’s no accident that Marcel Proust’s seven-volume Remembrance of Things Past was sparked by the flavor of a madeleine, or tea cake. That emotional pull may also explain why immigrants hold on to the flavors of their native country long after they’ve adopted new languages, new modes of dress—even, sometimes, new religions. Food binds ethnic groups together across generations and across oceans and national boundaries. We so often use flavors as ethnic markers, with the treasures of one culture being seen (at least initially) as disgusting by others. The French have their stinky cheeses, the Americans their peanut butter, the Australians Vegemite, and the Japanese the mucilaginous fermented soybeans known as natto.

  For many of us, venturing outside our own ethnic markers is one of the best bridges into another culture. “I’ve been to many countries in the world, and one of the things I’ve done in every country is visit food markets,” says Breslin. “I’ve never really thought about why that is, but I can’t imagine not doing it. It’s always been a rewarding experience.” Most people share that response to some degree. Who, after all, would take a trip to Italy and eat only at McDonald’s, or live on pizza in China?

  The roots of flavor, it seems, run deep into the human condition. But flavor also spices our daily life. All of us have to eat every day, and most of us seek out tastier foods when we have the choice. Grocery shoppers consistently report that flavor is their main guide in deciding what to buy each week, trumping considerations of health, price, and environmental impact. And people rate the pleasure of a fine meal higher than sports, hobbies, reading, or entertainment. Only holidays, sex, and family time ranked higher. And when asked why that fine meal is so pleasurable, more people cite flavor than any other reason.

  For millions of people, the act of cooking a daily meal is a creative, rewarding experience. If you’ve picked this book off a bookshelf, you’re probably one of that group. I know I am. We read cookbooks, trawl the Internet for interesting new recipes, and gradually build our kitchen repertoires. Yet most home cooks approach flavor haphazardly. We do what the recipe says, or what we’ve always done. Sometimes we mix things up by following our intuition and tossing in a handful of basil or sprinkling a grating of nutmeg. But we’re just following instructions, or intuition, or tradition; we lack the deeper understanding of flavor that could give shape to our efforts. In a way, we’re like the self-taught guitarist who can copy riffs by ear but can’t read music and has no formal training in harmony. We bumble along pretty well, and occasionally stumble on something that works beautifully. But think how much more we could accomplish with a better understanding of what we’re doing.

  For an eye-opening (palate-opening?) demonstration of how little most people know about flavor, take what I call the jelly bean test. Get hold of some jelly beans or other candies that come in a mix of flavors. The fancy, many-flavored jelly beans you can buy everywhere these days are ideal, but a tube of rainbow-flavored Life Savers would work just fine, too, or Jolly Rancher hard candies. It doesn’t matter—the important thing is just that you have several flavors to choose from. Now close your eyes, pinch your nose, and have a friend hand you one of the candies. Pop it in your mouth—still pinching your nose—and pay attention to the flavor. Not much there, right? You’ll get the sweetness of the sugar, of course, and maybe a little sourness or saltiness, depending on the candy. But what flavor is the jelly bean? You won’t be able to tell.

  Now release your nose, and see how the flavor suddenly explodes into your mouth. What was once merely sweet and a bit sour is now suddenly LEMON! or CHERRY! What’s changed is that you’ve brought your sense of smell into the game. The lesson here is that what appears to be a simple taste perception is more complex than we realize: Even though we refer to the “taste” of the jelly bean, taste itself is the least important part of the equation. Most of the flavor we actually experience is the result of smell, not taste. (For an even more vivid illustration of this point, hold your nose and try to tell the difference between a cube of apple and a cube of onion. It’s harder than you’d think.)

  The English language contributes to the confusion. We have separate nouns, “taste” and “flavor,” but we use them in greatly overlapping ways. Decades ago, psychologist Paul Rozin found that English speakers generally use taste when they’re referring to sweet, sour, salty, and bitter, which—along with the less widely known umami—form the five basic tastes that our tongue can detect. But we use taste and flavor almost interchangeably to refer to the bigger picture—the whole jelly bean, if you will. And when it comes to verbs, we make no distinction at all, using taste for everything, all the time. We say that dinner tasted good and mean much more than merely that it was properly salted and not too bitter. Indeed, when we have a cold we say we can’t taste anything—even though, in fact, taste is all we have left when our nose is plugged. One word, two meanings—that just about guarantees confusion. We also have the verb “savor,” but it doesn’t help much. To savor something usually implies that we ate with pleasure. No one would say, “I savored dinner and didn’t like it.” (Other languages are no better. Rozin polled native speakers of nine other languages and found that most use just a single word to cover both taste [in the strict sense] and flavor. Only two—French and Hungarian—have two different words, and even the French blur the distinction somewhat.) There’s no easy solution to the confusion. Throughout Flavor, I do my best to be clear about whether I’m talking about a taste or a flavor, but I fall back on the verb “taste” for both. I hope the context clarifies which meaning I intend.

  In fact, flavor has even more dimensions than just taste and smell. Every one of our five senses—taste, smell, touch, sound, and even sight—contributes meaningfully to the way we perceive flavor. The best way to think about flavor is that it is the sum of all the sensations we get when we have food in the mouth. That leads to some surprising discoveries: the weight of a bowl, the color of a plate, the crunch of a potato chip, and even the choice of background music can have a direct effect on how we perceive flavor.

  The meals we cook and the foods we eat are more than just a daily source of pleasure, of course. They also affect our health in profound ways. That’s especially true now, when poor diet and excess calories have fed an epidemic of obesity that threatens, for the first time in centuries, to shorten our life expectancy. More Americans are overweight than not, and the rest of the Western world is catching up quickly. Many experts point to our taste for sweetened soft drinks and high-fat, high-carbohydrate, high-calorie fast food as a primary cause.

  Once again, that puts flavor at the center of the picture. If we’re to do something about obesity, as individuals and as a society, we’ll need to understand why we eat what we eat. We’ll need to know how flavor drives our food choices, and whether we can use it as a lever to shift our consumption patterns. We’ll need to understand how flavor helps tell us when we’re full, and whether we overeat when meals are especially tasty. These turn out to be complex questions th
at scientists don’t fully understand yet, but some of the answers they’ve found may surprise you.

  Until recently, a book exploring the science of flavor would have been much shorter and more limited in scope. Within the past few years, however, scientists have made huge strides toward understanding every step of the pathway from food to perception to behavior. It’s no exaggeration to say that the science of flavor is one of the fastest-moving and most exciting disciplines around these days. A large proportion of the hundreds of scientific papers I read in the course of research for this book are just a year or two old. No doubt even more big discoveries await in the next few years. And as a bonus, it’s science that everyone can relate to, because it’s about the foods we eat every day, the pleasure we take in a glass of wine, a mug of beer, or a cup of coffee, and the question every one of us faces every day: What would I like to eat for dinner?

  In the early 1990s, biologists Linda Buck and Richard Axel identified the receptors responsible for detecting odor molecules, work that earned them a Nobel Prize in 2004. With receptors finally in hand, and aided by the human genome sequence completed early this century, other researchers are racing to crack the code by which the nose encodes the many different smells—possibly many millions—that compose the flavors of the foods we eat. Others are identifying the chemical receptors that detect a chili pepper’s fire and the cool of mint. Even the five basic tastes that we’ve known for a century are having to share the tongue with at least one, and possibly several, other tastes, as we’ll see.

  As scientists refine our understanding, we’re coming to realize that every person on the planet lives in their own unique flavor world defined by their genetic endowment, their upbringing and later food experiences, and the culture in which they live. We’re beginning to learn how these unique flavor worlds help define some of our strong likes and dislikes for certain foods. Take for example, former U.S. president George H. W. Bush’s famous distaste for broccoli. (“I do not like broccoli,’’ Bush told reporters back in 1990. ‘‘And I haven’t liked it since I was a little kid and my mother made me eat it. And I’m president of the United States, and I’m not going to eat any more broccoli!’’) We can’t know for sure without testing the former president’s genes, but it’s a pretty good bet that Bush carries a particular genetic variant of one specific bitter taste receptor, which makes broccoli and other mustard-family vegetables taste especially bitter to him. Your own genes undoubtedly shape your food preferences in similar ways—although genetics is not destiny: not everyone who tastes the bitterness hates it.