The best place to start when learning about perfumery materials is with the naturals. Learning these will give you a good frame of reference before moving on to the synthetics. So what makes a material a “natural” in perfumery terms?
Natural materials are defined as being those produced by a physical rather than chemical means of separation.
The part of the plant used very much depends on the material in question and some plants produce more than one type of aromatic substance.
For example the bitter orange tree produces Neroli from the flowers, bitter orange oil from the peel of the fruits and Pettigrain from the distillation of the twigs and leaves.
Other parts of plants can include:
Ariel Parts: Lavender, Rosemary
Wood: Cedarwood, Sandalwood
Flowers: Rose, Jasmine,Ylang
Berries or Seeds: Coriander, Juniper
Peel: Orange, Lemon, Bergamot
Resin: Olibanum, Myrhh
Production Methods Classed as Natural:
The majority of citrus oils are produced by expression as distillation creates an inferior product; the exception to this is lime where steam distillation is most often used. The peel of citrus fruits contains tiny oil sacs that you will notice when you peel and orange for example. The oil is mechanically expressed by rupturing these sacs and separating the oil from any juice present. Citrus oils have a fairly short shelf life and are prone to oxidation, they should be stored away from heat and light in tightly closed full containers. Citrus oils may be rectified to create a more stable product for use in fragrance as well as to remove any problematic components such as the furanocoumarin – bergaptene in Bergamot oil. Bergaptene is known to cause a phototoxic reaction on the skin and you should therefore only use furanocoumarin free bergamot oil.
Steam or Water Distillation:
Steam or water distillation is used to extract the volatile components of the plant and whilst this is considered to be natural we have to be clear on the fact that the very act of processing the material in this way will change it from how it naturally occurs in the growing plant. Some materials such as clove are extracted via water distillation it is a slow process and any plant material that is too delicate to undergo the the prolonged heating involved is steam distilled instead.
The process of steam distillation is very simple and has been done for centuries. The water is heated in the still with the plant material held above but not in contact with the water. As the water heats up and turns to steam it carries the volatile components through a pipe into a condenser where it is cooled and turned back into a liquid. The water and essential oil from this liquid are then separated and the resulting water is often sold as a hydrolat or flower water.
Another method of collecting the volatile parts of a plant with steam is fractional distillation. As different points in the distillation process different volatiles or portions of the distillate are collected. For example with Ylang Ylang there are several grades. Ylang Complete is produced using the full distillate. Ylang extra is the first collection of oil over several hours and is the highest quality. Ylang grades 1 to 3 are collected at increasing intervals with 3 being the final and poorest grade.
Natural isolates can also be produced by fractional distillation although in many cases it would be too costly to do so and so they are recreated synthetically instead. Naturally occurring materials such as Eugenol, Geraniol and Citronellol can be isolated for use in perfumes separated from their original source. Another method used to isolate the chemical components of naturals is freezing to produce crystals as is the case with Menthol.
Materials that cannot be economically distilled are extracted with the use of volatile solvents. Solvent extraction can remove different parts of the plant which are lost in the distillation process and so often you may see an essential oil and a solvent extracted absolute of the same plant. Both will have a slightly different aroma due to differing components being present in the extract. During the extraction process the material is gently washed with the solvent until as much of the essential oil as possible had been dissolved. Once the material is exhausted the solvent containing the dissolved essential oil is then distilled. This process is to remove the solvent leaving behind the extracted matter known as a concrete. The concrete is further processed to produce an absolute for use in perfumery. Resinous extracts produced in this way are known as resinoids.
Supercritical C02 Extraction:
Extraction by Carbon Dioxide is increasing in popularity due to its advantages over solvent extraction. Carbon dioxide as a solvent is preferable due to its low toxicity and flammability. It is also used a a low temperature giving it an advantage over steam distillation for many materials.
Some materials such as Ambergris are ground to a powder and macerated over a period of time in alcohol to create a tincture. Tincturing is another way to extract plant material but does not produce a very strong aroma in most cases.