Nose Dive: A Field Guide to the World’s Smells

No matter where or how you’re reading these words, at this very moment there’s a world swirling all around you, and into you, that teems with the makings of delight, disgust, understanding, and wonderment. It’s an invisible nimbus of flying molecules: countless specks of matter launched into the air we breathe, whizzing at highway speeds, whose presence we perceive as smells. This book is about those specks and smells, and about making the most of our access to them. Many fine books have been written on our sense of smell, on the pleasing aromas of food and drinks and perfumes, on the nature of disgust. Here I’ve put together something different: a guide to the wide world of smells, nice and not, and the airborne molecular specks that stimulate them. Since the specks are representative bits from throughout the material cosmos, I like to call this wide world the osmocosm, from osme, the ancient Greek for “smell” or “odor,” with its inner resonance and hint of wizardly magic. The osmocosm contains multitudes—thousands of different molecules at least, possibly thousands of thousands. There’s more to it than even the most sensitive among us can experience. And much or all of it is inaccessible to the many people whose sense of smell has somehow been impaired. But no matter how much of it we happen to notice, we’re always immersed in the osmocosm. It’s a fundamental feature of the world we inhabit. It’s well worth exploring, even if only in imagination and thought. The general term for any airborne molecule is volatile, a word that derives from the Latin for “to fly” and was first applied centuries ago to birds and butterflies and other winged creatures. It was one of these original volatiles, a flavorful wild bird, that drew me into exploring the world of molecular volatiles. Let me explain how it did, and how I hope you’ll use this guide to become a smell explorer yourself.   My longtime beat is the science of cooking. Back in 2005, when experimental cooking was the talk of the restaurant industry, I traveled to Spain and England to get a taste of its innovations. The leading avant-garde chefs, the Adriàs and Rocas and Heston Blumenthal, aspired to give diners an unforgettable meal, with long menus of novel dishes that were variously startling, amusing, baffling, and sometimes delicious. It was a stimulating few days. But my most memorable mouthful came near the end, during a very traditional British lunch with Fergus Henderson and Trevor Gulliver at their London restaurant St John. It was early fall, so I ordered grouse, a game bird just then in season that I’d never had the chance to taste. It came roasted whole and plainly, on a slice of toast, with a tuft of fresh watercress. I expected to enjoy it, but not that the first bite would leave me speechless. It did. I was completely absorbed, first by intense sensation—a meatiness that was almost too strong to be pleasant, and edged with bitterness—and then by confused emotion. I was momentarily paralyzed, unable to say a word to my tablemates. They looked at me with some concern, but then Fergus smiled, nodded, and said: “Ah, of course. Your first grouse.” I’d always been interested in understanding what makes foods delicious, but that experience impressed me like no other with the power of flavor to trigger strong feeling—and to persist. That grouse was still in my mouth many hours later as I tried to concentrate on a performance of Shakespeare’s Tempest. Another moment several years later impressed me with the power of aroma alone. I had managed to grow what looked like an oversized taste bud on the tip of my tongue, maybe an eighth of an inch across: a good joke for a food writer! Eventually I saw a specialist who advised removing it. He gave me a local anesthetic, snipped it out, then cauterized the wound with an electrical instrument that burns and seals the blood vessels. There was a puff of smoke, and I smelled the typical aroma of beef on a very hot grill, burned but also slightly decomposed. Unexpected, but it made perfect sense: it was the aroma of grilled McGee! Another good joke. And as I had that light-hearted thought, I got light-headed, then leaden-limbed, and broke into a cold sweat. The physician quickly reclined the chair, and in a couple of minutes I was fine again, just embarrassed. I had thought that I was taking the experience in stride, even relishing the irony, but my body ambushed me. Another unforgettable moment and smell. The cultural touchstone for connecting flavor with emotion is the morsel of madeleine cake that Marcel Proust’s narrator dunks into a cup of linden-blossom tea in the first of his seven volumes À la recherche du temps perdu, “in search of lost time.” That bite surprises the unnamed narrator with a shudder of “exquisite pleasure” that he eventually traces back to tasting the same combination in idyllic childhood. My shudders weren’t exactly pleasurable: they seemed more likely to be instinctive warnings. The grouse was so strong and funky that it might have been spoiled; cauterized tongue probably evoked the misery of my tonsillectomy twenty years before. But was that all they meant? Somehow there seemed to be more going on. My ruminations eventually led me to a less celebrated passage of Proust that resonated much more. In the penultimate volume Sodom and Gomorrah, the narrator indulges in a favorite drink and is struck by the sensations it provokes: the orange squeezed into the water seemed to yield to me, as I drank, the secret life of its ripening growth, its beneficent action upon certain states of that human body which belongs to so different a kingdom, its powerlessness to make that body live, but on the other hand the process of irrigation by which it was able to benefit it, a hundred mysteries revealed by the fruit to my senses, but not at all to my intellect. Once again a taste of food catches the narrator’s attention and triggers a feeling of elusive significance. But this time it’s not about his past life, it’s about the food. The orange somehow evokes the mystery of its creation and its goodness for alien creatures like us. The narrator doesn’t follow up this intimation the way he does the pleasure of the madeleine. But if he did, then his recherche would shift away from lost time and toward found fact, toward the natural histories and inner workings of fruit and animal. Proust’s orange encouraged me see my taste of grouse as an invitation to consider its mysteries. It was a call to stop and think and learn, to ask Why did that bird have such a strong and distinctive flavor? So I did ask, and I learned. Unlike domestic ducks and pigeons, British grouse are true game birds, living in the wild on open heathlands, constantly scrounging for food and evading predators, often infected with gut parasites that make them more easily scented by foxes and dogs. They’re driven from cover and shot on the wing, their carcasses matured—"hung”—for several days, guts included, to tenderize them and intensify their flavor. In 2007 I made a pilgrimage to western Scotland and shared an unforgettable weekend with St John’s game supplier Ben Weatherall and his family. I spent hours on Overfingland heath watching the birds, marveling at their explosive takeoff when flushed from the low brush, and their dazzling speed and maneuvers to hug the rolling hillsides until they were out of sight. No wonder their flight muscles are so dark with flavor-making metabolic machinery! I chewed the astringent, bitter heather they live on, and smelled the heaviness in the cool storeroom where they were hung. Harsh wild feed, powerful and well-exercised flight muscles, damaged guts leaking feed and digestive juices in a carcass on the cusp of decomposition: these are elements that combine to give traditional grouse its distractingly strong flavor. Having grown up in the prepackaged, sanitized, deodorized late twentieth century, with that initial bite I was tasting flesh for the first time, recognizing in my mouth the transfixing funk, chemical and emotional, of animal life and struggle and death. Yes, maybe a health warning, but at the same time so very much more! I felt my hunger for understanding satisfied, the experience retroactively enriched. And I got to wondering what meanings I might find hinted at in more ordinary eating experiences. Of course most foods just taste of themselves, as we expect them to from past experience. It’s the unusual, the incongruous that can capture the attention. I’d often been struck by the ways that unrelated foods can seem to echo each other. Parmesan cheese can taste like pineapple. What connection could there possibly be between old cow’s milk and ripe tropical fruit? Raw oysters can taste like cucumber. Sherry wine can taste like soy sauce, corn tortillas like honey—specifically chestnut honey. Even odder are foods that echo inedible things: the seaside in green tea, horse stables in wines, sweaty feet in cheeses. Thoughts of sea and stable and feet, and of grilled McGee, highlighted the fact that flavor echoes are similarities specifically in smells. Our sense of smell is the bridge between our experience of foods and our experience of the larger world. It normally accompanies every breath we take through the nose. We sense smells in the world when we breathe in, and flavors in the mouth when we breathe out. And smell gives us the most detailed, specific information of any sense about what’s around us or about to be swallowed. Pinch the nose and we can taste sweetness and sourness on the tongue, but we can’t tell a citrus soda from a cola; we can’t tell perfume from paint remover. It seemed to me that to understand the flavors of tea and wine and cheese would mean delving into the smells of oceans and animals and feet, to find out why they have the smells they do. This was a daunting prospect—but then increasingly exciting. In fact why stop at smells that happen to be obviously echoed in foods? Why not savor things in general the way we can savor food and drink, smelling them actively and curiously, learning from others about their backstories, and using that knowledge to experience them more fully? I got hooked. It was a kick to sniff at everything I could think of, then connect those immediate, personal sensations with precise laboratory identifications of the flying molecules that trigger them, and through the molecules, with the larger scientific understanding of the world’s workings. I often felt a sense of wonderment at those workings, and at the collective achievement of humankind in figuring them out. Despite its longtime reputation as one of the lowest of human faculties, smell clearly has the power to engage us with the world around us, to reveal invisible, intangible details of that world, to stimulate intense feeling and thought: to nudge us into being as fully and humanly alive as we can be.  So I became an amateur smell explorer and immersed myself in the osmocosm. I went on a ten-year sniffing expedition through the world and through the scientific literature. I’ve written this book to share what I’ve learned: to point out and delve into smells that are out there to be noticed, and to relate what those smells can tell us about how they came to be, about the otherwise insensible workings of the world. Not just food and drink and roses, but compost and sodden flowerpots, asphalt and laptops, old books and dog paws, the myriad mundane yet revelatory things that fill our lives. There’s a rich world of sensations and significance out there, intangible and invisible and fleeting, but vivid and real.   Now that I’ve explained the eccentric path by which I came to write this book, I should explain the eccentricities of the pages that follow: why they’re filled with what look like mashups of ingredient labels and tasting notes, and why the first chapter begins with the unsmellable Big Bang. Smell is such a powerful and revealing sense because it detects actual little pieces of things in the world. It gives us direct evidence of what those things are made of—unlike the indirectness of vision or hearing, which register light waves and air movements. Those little pieces are volatile molecules, so little that they’re able to break away from their source and fly invisibly through the air to reach our nose. To begin to understand a thing’s smell, then, is to identify the many volatile molecules it emits. Its overall smell is a composite, created by the component smells or “notes” of its most prominent volatile molecules. When different things seem to echo each other with shared component smells, it’s a sign that those things have some volatile molecules in common. And the chemical identities of the molecules are keys to why they’re there. They’re tokens of the processes that created them. So: much of this book is anchored in volatile chemistry. And chemistry of any kind is seldom an inviting subject for anyone but chemists! But I am not a chemist, and the chemistry in this book is not an end in itself. It’s a means of gaining insights into your own personal experience in the physical world, a means of smelling more and knowing what the smells mean. In fact, many of these molecules are longtime friends that that have been pleasing or annoying you all your life without your knowing they exist. We know and recognize and appreciate these significant bits of the world by smell, but they’ve never been properly introduced, individually and by name. The names that chemists have given them can be confusing at first, but they do have their own logic. And when we meet up with smells and named molecules often enough, the names begin to stick. These days many beer lovers can tell you about the esters and volatile phenols in their favorite ales; cannabis connoisseurs know their terpenes, craft perfumers their aldehydes. Because each chapter describes dozens of different things, each emitting many volatile molecules and component smells, I’ve distilled the relevant information in the smell tables that you’ll see throughout. They’re designed to make it easy for you to control your chemical exposure. Most of the tables have three columns. The first column lists a handful of related items of interest: particular parts of the body, or flowers, or cheeses. The second column lists some of the component smells that contribute to each item’s overall smell. These may look like tasting notes from ads and reviews, but they’re not merely subjective impressions. They’re the smells of specific molecules that have been objectively identified as significant volatiles in that item. Those molecules are listed in the third column. If you’re mainly interested in the component smells you might get a whiff of on your skin or in a some parmesan shavings, and you don’t want to be distracted by the chemistry, then just stay to the left and center of the tables. Simply paying attention to these nuances of smell can be rewarding. In a 1948 poem, the Scots poet Hugh MacDiarmid poked fun at the chemical approach of modern “osmology” while praising plain attentiveness: “a flower’s scent by its peculiarity sharpens / Appreciation of others.” But if you’re curious about why a gardenia smells so unlike a rose, why your skin sometimes has a metallic tang, or parmesan can seem both fruity and a little sickening, then look to the rightmost column to see what particular molecules are involved, and in the surrounding text to see where they come from. These details further sharpen appreciation and pleasure with understanding.   So much for navigating the tables; now for navigating the book as a whole. I’ve written this guide both for casual browsing and for learning about the greater osmocosm. It’s organized not by smells but by the familiar things in our world that emit them. So you’ll find the human body in chapter 6, flowers in chapter 10, cheeses in chapter 19. You’re welcome to head right for favorite or despised or newly encountered smellables. Or browse the pages and tables and see what catches your eye. For readers who want to explore the world of smells more systematically, and refresh their understanding of just what a molecule is, I’ve organized the chapters in a sequence that helped me get my own non-chemist bearings among volatile molecules, and that I hope will do the same for you. It emerged from pondering smell echoes: if oysters can smell like cucumbers, then which was the first to carry that particular molecule? And did something else carry it before either of them? I came to realize that like everything in the physical world, the molecules of smell have histories that are part of the ongoing history of creation itself, the evolution of the cosmos as a whole. That evolution started billions of years ago in the mysterious simplicity of the Big Bang, before there was a single molecule of any kind, and ever since has moved in the direction of increasing complexity. When I looked into the early history of the cosmos, I was fascinated to find that some of the molecules that we smell every day existed long before there was any creature around to smell them, before there was even a planet earth for creatures to live on. They’re among the simplest molecules, just a handful of atoms, as easy to grasp as H2O. Some of them remain the source of smells produced by most forms of life. And as life has diversified over the eons, so have the volatile molecules it emits. The simple is easier to understand than the complex, and it’s a stepping-stone to grasping complexity. So I’ve structured this book in five parts that introduce the molecules of smell a few at a time, roughly as they emerged. I invite the novice smell explorer to imagine yourself alongside the Chef of the cosmos, superhuman but with a human nose: sniff the stew of matter and energy as it cooks over the eons, notice how its smells develop, and become familiar with the increasingly complex—and pleasant!—molecules they arise from. Part One starts with the sparse primordial volatile molecules of outer space, the sulfurousness of Earth and its early single-cell life, and the basic starter set of volatiles and smells shared by all living things. Part Two documents how animal bodies, ours included, owe most of their smells to their mobility and the communities of microbes that they host. Part Three celebrates the creativity of the plant kingdom and its terrifically diverse volatiles and smells, fresh and woody and flowery and fruity. Part Four describes the smells that emanate from the planet’s waters and soils, and from life’s remains when they’re transformed into smoke and tar, fuels and plastics. And Part Five concludes with the smells that humankind loves and pursues for their own sake, in fragrances and foods and drinks.  Welcome then to the osmocosm, the world aswirl right under our nose.