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ROSE PICKERS OF PÉGOMAS: Workers rise each day at dawn for two weeks to pluck the fragrant flowers.

PARI DUKOVIC/TRUNK ARCHIVE

STANDARDS

NGSS: Core Idea: PS1.A

CCSS: Writing for Science Literacy: 2

TEKS: 6.2A, 7.2A, 8.2A, C.2E

What's in a Scent?

How chemistry helps perfumers bottle the smell of roses and other plants to create timeless fragrances

ESSENTIAL QUESTION: How might chemistry be important to perfume making?

Each spring, 70 workers descend upon the rose fields of Pégomas, France. Every day for two weeks, they’ll rise at dawn to harvest fragrant roses by hand. By the time their work is done, they will have picked about 37 tons of flowers—an amount comparable to the weight of five full-grown elephants.

The flowers are placed in burlap sacks and taken to a nearby factory within an hour of being plucked. Wait any longer and the molecules—two or more atoms chemically bonded together—responsible for the roses’ honey-like scent begin to break down. As soon as the petals arrive at the factory, they’re tossed into a chemical bath and heated. The liquid chemicals evaporate into a gas, leaving behind a wax that smells like a Pégomas rose (see From Rose to Perfume). A fragrant oil extracted from the wax will become the main ingredient in Chanel No. 5—one of the most popular perfumes of all time.

Each 30 milliliter (1 fluid ounce) bottle of Chanel No. 5 contains the concentrated scent of about 12 roses, along with dozens of other fragrant ingredients. The resulting aroma does more than just smell good. Scent is strongly linked to memory and emotion. Just one whiff of a perfume can evoke a different time, place, and feeling in your mind. For perfumers to create such compelling scents, they must rely on their noses—and chemistry.

Each spring, 70 workers head to the rose fields of Pégomas, France. They rise at dawn to pick sweet-smelling roses by hand. They’ll work every day for two weeks. When they’re done, they will have picked about 37 tons of flowers. That’s about the weight of five full-grown elephants.

Workers place the flowers in burlap sacks. Certain molecules—two or more atoms chemically bonded together—give the roses their honey-like scent.  The flowers are taken to a nearby factory within an hour of being picked. Wait any longer, and these molecules begin to break down. As soon as the petals arrive at the factory, they’re tossed into a chemical bath and heated. The liquid chemicals evaporate into a gas. That leaves behind a wax that smells like a Pégomas rose (see From Rose to Perfume). A fragrant oil is removed from the wax. It will become the main ingredient in Chanel No. 5. That’s one of the most popular perfumes of all time.

A bottle of Chanel No. 5 might hold only 30 milliliters (1 fluid ounce). But it contains the concentrated scent of about 12 roses, plus dozens of other fragrant ingredients. That creates a scent that smells good, but it does more. Scent is strongly linked to memory and emotion. One sniff of a perfume can make you think of a different time, place, and feeling. To create such appealing scents, perfumers must rely on their noses—and chemistry.

PARI DUKOVIC/TRUNK ARCHIVE

CAPTURING SCENT: Many perfumes contain scented oils extracted from natural ingredients like roses.

BOTTLING A SMELL

Imagine a fresh-mown lawn or a recently peeled orange. Each has its own distinct smell, caused by different kinds of molecules. When inhaled, these molecules bind to specialized scent-receptor cells inside a person’s nose. The cells then send a signal to the brain, which identifies the signal as scent.

For thousands of years, people have sought to capture the smells of nature and put them in a bottle. The easiest way to do this is to extract and collect fragrant oils that occur naturally in most plants, from roses and grass to oranges. “The oils you extract from nature are a complex mixture of maybe hundreds of molecules,” says Jen Bayline. She’s a chemist at Washington & Jefferson College in Pennsylvania who teaches courses on the chemistry of perfume. “Together, they create a rich and complex fragrance.”

Once an oil is obtained, perfumers often dissolve it in alcohol. This solution can then be easily sprayed to distribute the scent.

Think of a fresh-mown lawn or a newly peeled orange. Each has a one-of-a-kind smell.  Different kinds of molecules cause each smell. Breathe in these molecules, and they bind to scent-receptor cells inside your nose. Then the cells send a signal to the brain, and the brain identifies the signal as scent.

For thousands of years, people have tried to put the smells of nature in a bottle. The easiest way to do this is to remove and collect fragrant oils. These oils are found naturally in most plants, from roses and grass to oranges. “The oils you extract from nature are a complex mixture of maybe hundreds of molecules,” says Jen Bayline. She’s a chemist at Washington & Jefferson College in Pennsylvania, and she teaches courses on the chemistry of perfume. “Together, they create a rich and complex fragrance.”

When they get the oil, perfumers often dissolve it in alcohol. Then this solution can be easily sprayed to spread the scent.

RE-CREATING NATURE

Natural oils can be costly to collect. Chanel No. 5 is expensive in part because extracting the oils from Pégomas roses is a time-consuming and labor-intensive process. Most perfumers rely on cheaper synthetic scents instead to create their perfumes. These lab-made molecules smell a lot—but not quite exactly—like the scents found in nature.

Making a synthetic scent requires chemists to first identify the hundreds of molecules responsible for a particular natural smell. They then pick out just one or two of the molecules that contribute most to that scent. Finally, the scientists try to reproduce molecules with the same structure. To do so, they use specific chemical reactions in the lab. A chemical reaction transforms one set of chemical substances into another.

One molecule used to create a synthetic scent is isoamyl acetate. It’s naturally found in bananas and is responsible for the fruit’s signature smell. Bayline has her students at Washington & Jefferson College create this molecule in her chemistry class by combining a particular alcohol and a type of acid, a chemical that usually has a sour taste and eats away at other substances. Students know the reaction is working when a banana-like smell fills the lab.

Natural oils can be costly to collect. That’s one reason that Chanel No. 5 is expensive. Removing the oils from Pégomas roses takes a great deal of time and work. Instead, most perfumers use cheaper synthetic scents to create their perfumes. These lab-made molecules smell a lot like the scents found in nature. But they don’t match exactly.

Making a synthetic scent isn’t easy. First, chemists identify the hundreds of different molecules that create a natural smell. They then pick out just one or two of the molecules. These are the ones that provide most of that scent. Finally, the scientists try to create molecules with the same structure. To do so, they use certain chemical reactions in the lab. A chemical reaction turns one set of chemical substances into another.

One molecule used to create a synthetic scent is isoamyl acetate. It’s found naturally in bananas. It gives the fruit its one-of-a-kind smell. Bayline’s students at Washington & Jefferson College create this molecule in her chemistry class. They combine a certain alcohol and a type of acid. That’s a chemical that usually has a sour taste and eats away at other substances. A banana-like smell fills the lab. Then students know the reaction is working.

MAKING A PERFUME

It’s a perfumer’s job to mix together both natural and synthetic ingredients to create a new, distinctive aroma. But it isn’t just a matter of choosing scents that are interesting or pleasing to smell. Perfumers also have to consider how the scents will hit a person’s nose at different times, says Anne Serrano-McClain. She owns and operates a small perfumery called MCMC Fragrances in New York City.

Every type of scent molecule has a different volatility, or tendency to evaporate. Small, lightweight molecules evaporate quickly, so a person will smell them first. Large, heavy molecules have a low volatility and take longer to evaporate. A person may smell these scents for hours after applying a perfume (see Perfumer’s Pyramid).

It’s a perfumer’s job to create new scents. Perfumers do this by mixing together natural and synthetic ingredients. But they don’t just choose scents that are interesting or pleasing to smell. They also have to know how the scents will hit a person’s nose at different times, says Anne Serrano-McClain. She owns and runs a small perfumery called MCMC Fragrances in New York City.

Every type of scent molecule has a different volatility. That means some evaporate more easily than others. Small, lightweight molecules evaporate quickly, so a person will smell them first. Large, heavy molecules have a low volatility. They take longer to evaporate. A person may smell these scents for hours after using a perfume (see Perfumer’s Pyramid). 

“The hardest part about creating perfumes is that there are endless possibilities,” says Serrano-McClain. “There are about 1,500 scents that you can choose from, but only 20 to 50 of them wind up in the bottle.”

Some perfumers want their creations to tell a story or capture a feeling. Serrano-McClain often starts with the memory of a place she has visited. A recent perfume was based on several months she lived in Kathmandu, Nepal. She wanted the perfume to evoke the scent of jasmine flowers blooming in gardens, smoke from small wood fires used in homes around her neighborhood, and burning chai tea incense.

“The hardest part about creating perfumes is that there are endless possibilities,” says Serrano-McClain. “There are about 1,500 scents that you can choose from, but only 20 to 50 of them wind up in the bottle.”

Some perfumers want their scents to tell a story or capture a feeling. Serrano-McClain often starts with the memory of a place she has visited. She based a new perfume on Kathmandu, Nepal, where she lived for several months. Jasmine flowers bloomed in the gardens. Smoke rose from small wood fires in homes around her neighborhood. People burned chai tea incense. She wanted the perfume to capture these scents.

PARI DUKOVIC/TRUNK ARCHIVE (LEFT); COURTESY OF ANNE SERRANO-MCCLAIN (RIGHT)

  • RARE ROSES: Chanel uses special Rosa centifolia flowers. The name means “hundred petal roses” (left).
  • SCIENCE MEETS ART: Perfumer Anne Serrano-McClain works at her lab in Brooklyn (right).

Once she had her idea, she began experimenting by mixing together different scents that reminded her of those experiences. She started with natural jasmine and sandalwood oils, along with a synthetic scent that smells like chai. Then she complemented those scents with more than a dozen others. Once she had the ingredients figured out, she spent several weeks fine-tuning how much of each to include.

“You put the ingredients together, mix, smell it, and repeat,” says Serrano-McClain. “You just go through rounds and rounds of creating perfumes and evaluating them until you find the perfect one.”

When she had her idea, she began experimenting. She mixed together different scents that reminded her of those experiences. She started with natural jasmine and sandalwood oils, plus a synthetic scent that smells like chai. Then she added more than a dozen other scents. After she’d figured out the ingredients, she fine-tuned how much of each to include. That took several weeks.

“You put the ingredients together, mix, smell it, and repeat,” says Serrano-McClain. “You just go through rounds and rounds of creating perfumes and evaluating them until you find the perfect one.”  

CORE QUESTION: What are some differences between natural and synthetic scents?

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