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Authors: Avery Gilbert
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even have applications for environmental issues. Livestock feeding operations, for example, generate a big, messy stink that can annoy nearby residents. A typical Iowa swine barn contains more than 300 different volatiles, which sounds like a lot of bad news for the downwind neighbors. Yet a recent study found that four molecules account for about 85 percent of the piggy odor. One of these—para cresol—has a smell that by itself closely resembles the overall barnyard odor. This discovery may turn an overwhelming odor problem into a manageable project. Instead of going after all 300 suspect chemicals in the swine barn, one might suppress a handful of character-defining molecules. Pinpoint sensory targeting could produce bigger benefits at less cost.
T HE SUCCESS OF aroma models—those minimalist imposters—casts nature’s abundance in a new light. Lifelike smells can be made from a handful of molecules, and the same molecules turn up in smell after smell. Is nature’s chemical cornucopia really so impressive if only a tiny portion of it matters? And what does it say about our sensory abilities if there is so much more out there than meets the nose?
Terry Acree, the Cornell scientist who helped develop GC-olfactometry, has the numbers to back this up. He searched through hundreds of food-aroma studies and made a list of volatiles present at smellable concentrations. The first edition of the FlavorNet list was posted online in 1997. It contained three hundred chemicals. Today he has posted about eight hundred. Acree expects the list to top out at fewer than one thousand. In other words, all the smells in nature are built from fewer than one thousand smellable chemicals. What are those other thousands of volatiles doing? They may subtly round out a scent, give it shading and complexity. Acree speculates that many of them are intended for the noses of creatures other than ourselves; the scents of nature are largely a chemical conversation between plants and animals, and humans merely eavesdrop. Just as we are blind to certain patterns on the wing of a butterfly or the petals of a flower because we cannot see in the ultraviolet, our mammalian noses are not tuned to certain olfactory broadcasts.
It is odd to think that a childhood’s worth of olfactory memories can be boiled down to a pocket chemistry set. Were the tomato fields of Davis and the cooking ketchup of the Hunt’s cannery—so powerfully evocative to me as a kid—just a particular shuffle of sixteen key odorants? Evidently so. Knowledge also brings insight. I now understand in molecular detail why my grade-school field trip to the Spreckels Sugar Company plant was such a stunning disappointment. As beets are processed into pure white refined sugar they first release geosmin (damp earth) and dimethyl disulfide (onion, cabbage, putrid). Later comes propionic acid (the pungent, rancid note in Swiss cheese and sweat), and finally hexenoic acid (musty, fatty). Those four notes were the heavy stew that oppressed my soul that day in third grade. Somehow, knowing that makes me feel better.
CHAPTER 3
Freaks, Geeks, and Prodigies
D ON G IOVANNI :
Zitto: mi pare sentir odor di femmina!
[Hush! I think I scent a woman!]
L EPORELLO :
Cospetto! Che odorato perfetto!
[My, my! What a nose!]
D ON G IOVANNI :
All’aria mi par bella.
[And a pretty one at that.]
—M OZART,
Don Giovanni
T AKE A FEW DOZEN PEOPLE AT RANDOM, AND YOU WILL find a range of olfactory talent that stretches from
American Idol
–tryout bad to unbelievably excellent. There are people who cruise untroubled past the fetid plumes of garbage cans and subway vents, and others for whom the faintest milk fart escaping from an elderly relative is a nasal crisis. Olfactory sensitivity (technically, the lowest concentration at which someone detects a smell) is just one dimension of smell talent; other factors include an awareness of smells, and the ability to identify them and discriminate among
T HE SUCCESS OF aroma models—those minimalist imposters—casts nature’s abundance in a new light. Lifelike smells can be made from a handful of molecules, and the same molecules turn up in smell after smell. Is nature’s chemical cornucopia really so impressive if only a tiny portion of it matters? And what does it say about our sensory abilities if there is so much more out there than meets the nose?
Terry Acree, the Cornell scientist who helped develop GC-olfactometry, has the numbers to back this up. He searched through hundreds of food-aroma studies and made a list of volatiles present at smellable concentrations. The first edition of the FlavorNet list was posted online in 1997. It contained three hundred chemicals. Today he has posted about eight hundred. Acree expects the list to top out at fewer than one thousand. In other words, all the smells in nature are built from fewer than one thousand smellable chemicals. What are those other thousands of volatiles doing? They may subtly round out a scent, give it shading and complexity. Acree speculates that many of them are intended for the noses of creatures other than ourselves; the scents of nature are largely a chemical conversation between plants and animals, and humans merely eavesdrop. Just as we are blind to certain patterns on the wing of a butterfly or the petals of a flower because we cannot see in the ultraviolet, our mammalian noses are not tuned to certain olfactory broadcasts.
It is odd to think that a childhood’s worth of olfactory memories can be boiled down to a pocket chemistry set. Were the tomato fields of Davis and the cooking ketchup of the Hunt’s cannery—so powerfully evocative to me as a kid—just a particular shuffle of sixteen key odorants? Evidently so. Knowledge also brings insight. I now understand in molecular detail why my grade-school field trip to the Spreckels Sugar Company plant was such a stunning disappointment. As beets are processed into pure white refined sugar they first release geosmin (damp earth) and dimethyl disulfide (onion, cabbage, putrid). Later comes propionic acid (the pungent, rancid note in Swiss cheese and sweat), and finally hexenoic acid (musty, fatty). Those four notes were the heavy stew that oppressed my soul that day in third grade. Somehow, knowing that makes me feel better.
CHAPTER 3
Freaks, Geeks, and Prodigies
D ON G IOVANNI :
Zitto: mi pare sentir odor di femmina!
[Hush! I think I scent a woman!]
L EPORELLO :
Cospetto! Che odorato perfetto!
[My, my! What a nose!]
D ON G IOVANNI :
All’aria mi par bella.
[And a pretty one at that.]
—M OZART,
Don Giovanni
T AKE A FEW DOZEN PEOPLE AT RANDOM, AND YOU WILL find a range of olfactory talent that stretches from
American Idol
–tryout bad to unbelievably excellent. There are people who cruise untroubled past the fetid plumes of garbage cans and subway vents, and others for whom the faintest milk fart escaping from an elderly relative is a nasal crisis. Olfactory sensitivity (technically, the lowest concentration at which someone detects a smell) is just one dimension of smell talent; other factors include an awareness of smells, and the ability to identify them and discriminate among
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