How Is Perfume Made? Notes, Fixatives and the Chemistry of Scent

The raw materials come from two sources:

• •Naturals: essential oils distilled from flowers, leaves, woods, resins and citrus peel, or extracted with solvents into absolutes; a kilogram of rose absolute takes about four tonnes of petals, jasmine is picked by hand at dawn, sandalwood and oud come from trees that take decades, and the animal materials, musk from the deer, ambergris from the whale, civet and castoreum, are now nearly all replaced
• •Synthetics: single molecules made in the laboratory, some copies of natural ones, such as vanillin, and some that do not exist in nature, such as the aldehydes that gave Chanel No. 5 its shimmer in 1921 and the white musks that replaced the deer; synthetics are consistent, cheap and often cleaner in smell than the natural oil, and every modern perfume is mostly synthetic

Molecules evaporate at rates set by their size and their attraction to each other, and a scent is smelled only as it leaves the skin into the air. Small, light molecules such as citrus terpenes and the green notes of leaves are gone in fifteen minutes; the medium ones, most flowers and spices, last for hours; and the heavy ones, woods, resins, musks and vanillin, cling for a day. A perfume is composed as a sequence: the top notes make the first impression and sell the bottle, the heart is the character, and the base is what a person smells of at the end of the evening. The base materials are also fixatives, slowing the evaporation of everything else by holding it in a film, which is why a perfume with good musks lasts and one without vanishes. The concentration sets the rest: an eau de toilette is 5 to 15 percent fragrance in alcohol and water, an eau de parfum 15 to 20, and an extrait up to 40.

A perfumer, a nose, trains for years to recognise the materials blind and to know how each behaves with the others, and composes on paper before smelling, writing a formula of a few dozen lines that a laboratory weighs out in grams for trial. The great perfumes are built on accords, combinations of a few materials that read as one new smell, the chypre accord of bergamot, oakmoss and labdanum from 1917, the fougere of lavender, coumarin and oakmoss from 1882, the oriental of vanilla, amber and spice; a new perfume is usually a variation on one of them. Most commercial perfumes are made not by the brands whose names they carry but by a handful of fragrance houses in Grasse, Geneva, New York and Holzminden, which employ the perfumers and compete for briefs, and the brand's marketing budget is often larger than the cost of the juice by a factor of a hundred.

Smell works by molecules fitting receptors in the nose, of which humans have about 400 kinds, each responding to several molecules and each molecule to several receptors, so that a scent is a pattern of activation that the brain learns to name. There is no map from a molecule's shape to its smell, and chemists cannot yet predict what a new compound will smell of; the smell of a rose is a few hundred compounds of which one, phenylethyl alcohol, dominates, and the difference between a real rose and a rose perfume is the hundreds of trace molecules that no formula reproduces. Smell also goes to the parts of the brain that handle memory and emotion before it reaches the parts that name things, which is why a perfume worn by a person long ago can bring the person back, and why the industry sells memory in the shape of a bottle.

The Egyptians burned resins to the gods, which is what perfume, through smoke, means; the Persians and Arabs distilled rose water, and Avicenna's improvements to the still in the eleventh century made essential oils available; the Renaissance Italians scented gloves and Catherine de' Medici brought her perfumer to France, where Grasse, a tanning town that needed to cover the smell of leather, became the centre of the flower trade. Eau de Cologne, citrus in alcohol, was made in Cologne in 1709 and is still sold. The synthetic era began with coumarin in 1868 and vanillin in 1874, and the perfumes of the twentieth century, from Jicky in 1889, the first to use synthetics deliberately, through No. 5, Shalimar and Chanel's rivals, were compositions in which chemistry gave the perfumer smells that no flower had. About 2,000 new perfumes are launched a year, most of them variations, and the ones that last are the accords that a nose found first.

Getting scent out of a plant without spoiling it takes different methods for different materials. Steam distillation passes steam through leaves, wood or petals, carrying the volatile oils off to be condensed and separated from the water; it suits lavender and many woods but damages delicate flowers. Those are extracted instead with solvents, which dissolve the fragrant compounds along with waxes, producing a concrete that is then washed with alcohol to give an absolute. Citrus oils are simply pressed from the peel. An older method, enfleurage, laid petals on trays of cold fat that slowly absorbed their scent, and it is now almost abandoned as too slow and costly.

A more recent technique leaves the flower alone. In headspace analysis, a glass dome is placed over a living blossom and the air around it is drawn through a trap that collects the molecules it gives off. The sample is then separated and identified with gas chromatography and mass spectrometry, which reveal which compounds are present and in roughly what proportions. Perfumers use the result to rebuild the smell from synthetic materials, which is how the scent of flowers that yield no usable oil, such as lily of the valley, reaches a bottle. The same analysis lets rival companies study a competitor's perfume.

Within minutes of putting on a fragrance, most people can barely smell it, while others nearby still can. This is olfactory adaptation: the receptors and the brain circuits behind them respond strongly to a new smell and then turn down their response to a steady one, so that attention stays free for changes in the air. It is the same reason you stop noticing the smell of your own home. The perfume has not gone; you have stopped registering it, and people who keep adding more to make up for it often end up wearing far more than anyone around them would choose.

Adaptation also shapes how perfume is sold and tested. Smelling many scents in a row blurs them together, which is why some shops offer bowls of coffee beans to clear the nose, though experiments have found little evidence that coffee works better than breathing ordinary air or sniffing your own skin. Perfumers judge on paper strips called blotters and then on skin, because skin warmth, oils and moisture change how quickly each material evaporates. A sensible way to choose is to try no more than a few at once, on skin, and judge them again hours later, when the base notes are what remain.

Ambergris, one of the most famous perfume materials, is produced in the intestines of sperm whales, probably to protect the gut from the sharp beaks of the squid they eat. Lumps are expelled and can float on the ocean for years, slowly weathering from a sticky dark mass into a pale, waxy material with a sweet, earthy scent prized by perfumers as a fixative that makes other scents last longer.

Lumps occasionally wash up on beaches, and finders have sometimes sold them for large sums. Because sperm whales are protected, trade in ambergris is restricted in some countries. Most modern perfumes use synthetic substitutes, such as a molecule called ambroxide, which reproduces the warm character of ambergris without any need for whales.

Perfume is a formula of natural oils and synthetic molecules dissolved in alcohol at a few to forty percent, composed in top, heart and base notes according to how fast each material evaporates from the skin, with heavy base materials acting as fixatives that hold the lighter ones back. Perfumers build on classic accords from a palette of some three thousand materials, most modern perfumes are largely synthetic and made by a few fragrance houses, and the smell reaches memory and emotion before it reaches a name.