Throughout history humankind has tried to capture the ephemeral odours which fill its world. Many are still elusive, but many have been harnessed through the development and perfection of various processes. It is difficult for us to imagine in todays high-tech, scientific world that many methods still in use seemingly owe more to the alchemist than the chemist (take orris, for example, the iris rhizome has to have its roots, leaves, and flowers removed, before being dried for a minimum of three years which results in a hard, fossilised looking ‘stone’. It is now known as orris and has no real odour. Any sane person coming across it would have thrown it out, but someone in history decided to place it in alcohol and leave it there for two years. The orris dissolves into the alcohol, becomes yellowish in colour and looks like butter which has been left too near a hot stove. It is now known as orris butter, or beurre d’orris, and smells fatty, and in a vague way slightly violet-like—this is the first real glimpse of the beauty hiding within. The orris butter undergoes a final treatment to extract the oil which again does not truly reveal its hidden secret; it is only when it combines with other materials that its inherent soft, luxurious, powdery magic reveals itself. Today, the way orris is processed has not really changed, and because of this it is one of the most costly ingredients.
Compare this to one of the more recent techniques, such as ‘head space’, where man continues to try to capture the smells of nature. However, as many ingredients will not yield oil, head space technology is often deployed which records the emanations from a flower, etc., in the form of a gas chromatograph. This is then taken to a laboratory where scientists try to replicate the odour. One of the first scents to use these newly replicated odours was Red, by Giorgio Beverly Hills, in 1989. This discovery, along with other advances in the generation of synthetic materials, is used extensively in mass-market perfumery and commonplace in the so called ‘fine perfumery’.
There are various methods which are used throughout the industry to remove scented oils from raw materials. Each of the manufacturing houses will use these methods, but each will vary, leading to the specialities which are synonymous with each company. The method used for a particular ingredient is determined fundamentally by the characteristics of the raw material and, in some cases, by the effect desired by the perfumer.
OPPOSITE: A composition laboratory in Grasse, 1930. Courtesy of Alpes-Maritimes departmental archives.
Steam distillation has been known about for millennia, but it was the Arabic doctor and philosopher, Avicenna, who perfected it in the tenth century. The structure of the material being processed has to be taken into account to ensure the oils can be removed easily during the process: for example, mosses are generally softened by spraying them with water, woods are often finely grated, seeds crushed, whereas leaves and flowers need no pre-preparation as the cells containing the oils are thin walled and the oils can be removed very easily.
The raw material is placed on a grille suspended inside the still, water is put into the bottom, which is brought to the boil and turns to steam; as heat rises, the steam makes its way towards the top of the still, passing through the raw material en-route. The steam opens up the oil ‘cells’ and the oil becomes suspended in the steam as it passes out of the still via the ‘swans neck’ towards a condenser. As oil and water do not mix, the steam turns back to liquid and the oil and water separate. The resulting oil is known as an essential oil, whilst the water, which retains a small trace of scent, is known as floral water—the two most famous are rose water and orange flower water.
Scientists had tried using solvents to remove scented oils as far back as the eighteenth century, however, their attempts were often literally explosive. It was not until advances in organic chemistry led to the discovery of benzene and hexane that solvent extraction became feasible. The advantage of these two solvents was their ability to dissolve the fragrant oils, whilst at the same time being easy to ‘evaporate off’. The advantage of this method is that the oils are true to the smell of the plant, which was not always the case with steam distillation, and once perfected it meant that enormous quantities of material could be treated at one time.
The vessels used for solvent extraction are usually made from stainless steel and can contain between 3,000-4,000 litres. The raw material being treated is placed on one of many trays which have holes over their surface, allowing the solvent to pass through the material. The advantage of the trays is that they stop the material compressing and allow for huge quantities of material to be placed inside the container. The solvent is then mixed with the raw material; the length of time it remains in contact with it varies from one material to another. The oils will mix with the solvent and the remaining raw material once spent is discarded. The resulting mixture is decanted to remove moisture and generally undergoes a partial distillation under reduced pressure leaving behind a thick, waxen paste which has to be processed to remove its valuable oils. The name of this paste will vary depending on the type of material treated.
If a dry material, such as a wood, has been treated the resulting paste is known as a resinoid whereas, if the material was fresh (such as a flower) the paste is known as a concrete. The concretes have to undergo further treatment to remove their precious oils as they contain waxes which are insoluble in alcohol. Depending on the material which has been treated the mixture is cooled to somewhere between minus ten and minus 15 degrees Celsius so that it becomes solid. The concrete then undergoes repeated ‘washings’ with alcohol, during each of them the fragrant oils mix with the alcohol leaving the waxes behind. The waxes are discarded leaving a mixture of alcohol and oil which is heated at reduced pressure to ensure that the oil is not damaged, the alcohol evaporates, leaving behind a substance known as an absolute. Absolutes are generally full bodied and sensual.
Expression is used solely to treat citrus fruit; the resulting oils are often known as hesperidic oils and, when blended, as a hesperidic accord. The name is derived from Greek mythology and the ‘Garden of Hesperidia’. One of the ‘ 12 Labours of Hercules’ was to steal from the garden the ‘apples of immortality’ which were protected by the 1OO-headed dragon, Ladon. When this was completed he found that the golden apples where in fact the citrus fruit, orange.
The oil cells are contained within the skin and are easily opened by applying pressure to them. Citrus oils used to be obtained by squeezing the pre-softened rind by hand, which had been soaked in warm water to facilitate the process. The oil was collected on natural sea sponges as they completely absorbed the oil and ensued that literally not one drop was wasted. In Calabria, the traditional home of bergamot, the oil was also extracted by hand but by using special gloves made from leather with a surface made from pumice stone.
Today the rinds are placed between mechanical crushers that literally squeeze, or ‘express’, the oil from the skin. As the oil is removed so is a portion of water, which is not wanted, and this is generally removed using a centrifuge. The resulting oils are known as essential oils and are brisk, fresh, airy and enlivening.
This method was invented by the French perfumer, Piver, in 1750, and exploited the natural phenomenon of fat absorbing odour, to remove the scent from delicate flowers such as tuberose and jasmine. It was a great improvement on an earlier, now defunct, method known as enfleurage chaud,where flowers were immersed in hot fat, ruining the odour of the flower as it cooked, whilst leaving a waxy-fatty residual odour behind.
With enfleurage, glass plates (held in a wooden frame known as a chassis) are covered with a thin layer of highly refined, odourless fat. The fat is combed so that air can circulate around each blossom. The blooms, which are picked by hand, are laid onto the fat at precise intervals, which is where they are left until they have yielded their entire odour. The time involved in this process varies depending on the material—in the case of tuberose it is generally three days, whereas jasmine requires one day.
The flowers are then removed by hand, whilst fresh flowers are being picked in the fields. The process continues until the fat becomes saturated with oil, at which stage it is known as ‘pomade’. The pomade is then washed with alcohol and mixed with the oils, with the residue wax being discarded. This mixture is then heated, leaving an oil known as an obsolue de pommade. The Grasse-based distillery house, Robertet, is really the only company left who still produce oils by this method. It is an incredibly expensive process—due to the amount of handwork it entails—and so is only reserved for the very finest fragrances. There are only a handful of people left in the world with the skill and experience to employ this technique and, with the lack of demand due to high prices, the resulting absolutes command it won’t be long before it fades into history.These oils are absolutes, as are those obtained by solvent extraction, which was the method that largely superseded this labour intensive one.
A tincture is where a raw material is placed in alcohol and left to macerate. It was the process used for the animal notes and is still used for materials like vanilla. All that is needed is alcohol, the raw material and patience, as the oils contained in the raw material will eventually seep into the alcohol and scent it.
Naturally occurring excretions from trees—known as gum resins, such as myrrh, benzoin, or frankincense—were traditionally treated by placing them in alcohol to form tinctures but, today, they are often treated with solvents.