The natural perfumer’s palette: How botanical scents are captured
Fragrant plants contain aromatic compounds called essential oils. These compounds are found in the different parts of the plant - in their flowers, bark, rinds, leaves, roots, sap and seeds, and serve either to lure pollinators and propagators, or to defend against pests and predators. Essential oils often have therapeutic and antimicrobial benefits, and are especially delightful to the natural perfumer.
To capture the scent of a plant, we must separate its aromatic essential oil from its fiber, juice, wax, and sugars. How this is done depends on the plant’s composition and heat tolerance.
The journey of the orange tree
The orange tree is unique and highly valued in perfumery as it is the only plant that produces four unique essences from one tree. Its rind, flowers, leaves and twigs can be expressed, distilled and extracted, making it the perfect plant to illustrate the different methods and types of natural perfume materials.
Expression and Essential Oils
Also called cold-pressing, expression is an easy and inexpensive way to separate a plant from its essential oil. Expression is typically used for capturing the essential oils of the orange and other citrus fruit, like limes, bergamot and yuzu, as their essential oils are uniquely found in their peels.
How expression works: capturing orange essential oil
- A machine washes and separates the rind from the flesh and pith of the orange.
- The rind is then pressed through rollers, resulting in a slurry of juice, wax and essential oil.
- This slurry is separated via centrifuge and the essential oil is saved.
Distillation, Neroli, Petitgrain and Floral Water
An ancient method of selective boiling and condensation, distillation has been used for thousands of years to refine materials and separate organic matter. In the words of world-leading spirits expert and whiskey sommelier Heather Greene, “The whole idea [of distillation] is inspired by nature: Puddle water turns into invisible vapor after a day of hot sun. A cool evening reverses the process, and droplets of water form on blades of grass.”
A little chemistry lesson
Volatility measures how easily a substance evaporates. All citrus essential oils and others like fir needle and lavender are fairly volatile, while others like clove, cedarwood and ambrette seed are less so. Solvents like alcohol and hexane are highly volatile (and flammable). It is this property of volatility and the different boiling points of the chemical components found within the plant that enables us to capture a plant’s essential oils through distillation and solvent extraction.
Today distillation is used to desalinate water, distill and concentrate alcohol, and most importantly for perfumers, to capture the essential oils and floral waters of plants that are not overly sensitive to heat damage. Typically, steam distillation is used to capture the perfumer’s essential oils, as it is gentler on the plant than water distillation.
How distillation works: capturing neroli and petitgrain
- Essentially, steam is used to vaporize the orange tree’s volatile aromatic molecules.
- After cooling, the vaporized gas condenses into two substances; a water based hydrosol (also called floral water) and the essential oil.
- Because oil and water do not mix, the essential oil is easily separated from the floral water. Neroli essential oil is the term used for the essential oil obtained from the orange flower, and petitgrain refers to the essential oil distilled from its leaves and twigs.
Isolates and rectified oils
Essential oils have dozens and sometimes hundreds of molecular components. Sometimes it is desirable to isolate one molecule from the rest, or to remove specific molecules or impurities from the whole. This can be done through fractionated distillation, where the oil undergoes a series of distillations called rectification to produce an oil of a higher purity. This results in rectified essential oils like ylang ylang I, II, III, and safe bitter almond oil (unfractionated it contains arsenic), and natural isolates like damascenone from anise and ambrettolide from hibiscus.
Types of Solvent Extraction, Concretes and Absolutes
Sometimes the high temperatures of distillation damage fragile essential oils. Solvent extraction is an alternative method that captures the scent of more delicate plants - typically flowers. It is also used for plant materials yielding low amounts of essential oils or those that are considerably resinous, and can be likened to ‘dry-cleaning’ plants to release their essential oils.
In chemistry, a solution happens when a solute (here a fragrant plant) is dissolved in solvent. So a solvent is a liquid that can dilute compounds. Alcohol and hexane are popular solvents, and are also highly volatile (meaning they evaporate quickly).
Enfleurage, hexane solvent extraction, supercritical CO2 extraction, and maceration are all types of solvent extraction, and are used to create pommades and absolutes. Essentially, a plant is soaked in a solvent - hexane, CO2 or fat, depending on the process - to dissolve any essential oils. This produces a waxy aromatic paste, called a concrete or pommade, which contains non-volatile plant material such as waxes and pigments in addition to the essential oils. The residual plant materials are then separated by an alcohol wash, and the solvent removed, resulting in a thick, viscous absolute. Absolutes and pommades are much more concentrated and longer lasting than essential oils, and are often described as being truer to the original plant in scent.
How hexane solvent extraction works: capturing orange blossom absolute
- Orange blossoms, placed on racks in a hermetically sealed container, are washed in hexane.
- Because hexane is highly volatile it is easily removed, resulting in an aromatic concrete, a combination of essential oils and plant waxes.
- The concrete is repeatedly washed with alcohol to dissolve the wax. What remains is viscous and highly fragrant orange blossom absolute.
Supercritical CO2 extraction
CO2 extraction is similar to steam distillation and hexane solvent extraction, but instead of steam or hexane, carbon dioxide is used as solvent. Because CO2 extraction requires a lower temperature than steam distillation (100 F vs 140 - 212 F), and the gaseous CO2 evaporates completely, CO2 extraction often results in a truer-to-life representation of the plant than steam distillation.
Enfleurage and Pommades
Translating to ‘in-flower’, enfleurage refers to the process of infusing flowers in fat, as their volatile aromatics are fat-soluble. Dating back to the 18th century in France, but no longer commercially viable aside from artisan micro operations, enfleurage is an extremely time consuming and manual nature. A thin layer of solid, odorless fat is spread on a glass plate, called a chassis. Petals are placed upon the fat and allowed to soak for one to ten days, after which they are discarded and replaced with fresh flowers. This ‘recharging’ must be done dozens of times to create a highly saturated, aromatic pommade. Sometimes the pommade is washed with alcohol to produce an absolute and fragrant fat. The aromatic flower-soaked fat can then be used to make naturally-scented soap!
Macerations, Tinctures and Extracts
This simple process involves infusing raw aromatic materials, like resins or balsams, in a carrier oil or alcohol. The aromatic material can be ground to increase absorption, and in the case of an oil maceration, is also dehydrated to avoid contamination. The resulting liquid is filtered to remove particulates and is now called an extract. Vanilla extract and truffle oil are examples of common household extracts.
Determining quality: all naturals are not created equally
The quality of an essential oil, concrete, absolute or pomade is determined by many factors, from the aroma of the original plant and its terroir to the way it is processed and stored.
Natural oils can easily be contaminated, adulterated or oxidized anywhere along their journey to the perfumer and wearer. An experienced perfumer will select materials for their perfume organ and formulations based on their quality and desirable facets.
Working with, smelling and daydreaming about raw plant aromatics is the best part about being a natural perfumer. The intensely beautiful, living ingredients demand one’s attention, appreciation and respect. In each 55 mL bottle of Tangled Garden eau de Parfum, there are the oils of 120 rose, 60 orange blossom flowers, 15 tangerines and 90 black currant buds. Anointing oneself with this fragrance is truly an act of pleasure, reverence, and communion with nature.
A note on natural isolates
Isolates can be obtained naturally, synthetically and bio-synthetically. Let’s use the example of vanillin to examine the different types of isolates. Synthetic vanillin can be made very cheaply by a number of common organic chemistry reactions, some of which render it useless for food/flavor use. ‘Bio-synthesized’ vanillin’ can also be made inexpensively, using modified strains of fungus or bacteria, to produce a form of synthesized vanilla that is food safe.
Natural vanillin is obtained through fractional distillation. The Natural Perfumers Guild defines natural isolates as “natural occurring chemicals (single chemicals) that have been “isolated” from their natural sources using the least invasive methods of extraction, usually fractional distillation. They have been extracted by purely physical means and have not undergone any chemical transformation.”
In compliance with the Natural Perfumers Guild, House of Forbidden Fruit only uses natural isolates. For example, my natural vanillin is isolated from cloves.
