There are several methods for extracting aromatic compounds from plant material: maceration, enfleurage, solvent extraction, gas extraction, pressing and distillation. Each suits different plants, and each gives a different product.
Where extraction began: alchemy
"Solve et coagula, et habebis magisterium." Dissolve and bind, and you will have the magistery.
Alchemy is the ancient art that brought us the practice of extraction and distillation. It is the art and science of separation, purification and cohobation. The quest of the alchemist was to separate the most basic elements in nature, as those elements were known at that time, and to recombine them to create things which had never existed. Alchemical practice is the foundation of chemistry.
- Separation through fermentation or maceration.
- Purification through heat, distillation or calcination. Calcination is the process of heating a solid (such as an ore) in air below its melting point to effect thermal decomposition or phase transition, or to remove volatiles, thereby changing the original solid into something else. Heating calcium carbonate to release CO₂ gas and form calcium oxide is one example.
- Cohobation, or recombination, is called the "Chemical Wedding".
Maceration
Maceration is soaking raw material in water or vegetable oil. Making tea at room temperature without boiling the water is one type of maceration.
Placing dry plants in vegetable oil is another type of maceration. Sweet almond oil, jojoba oil or any other base oil can be used for macerating plants. This is an ancient method for extracting aromatic compounds from plants. The end product is not a pure essential oil. It is a mixture that contains the essential oil and the vegetable oil.
Enfleurage
Enfleurage is cold or hot fat extraction. Cold enfleurage uses odorless fats that are solid at room temperature. Traditionally, lard or tallow is used.
A large plate of glass is first coated with odorless fat, and flowers are placed on top. The fat absorbs the aromatic compounds found in the flowers. The flowers are left on the fat for between 1 and 3 days. They are then removed, and new flowers take their place. This continues until the perfumer is pleased with the aroma of the scented fat. This first product is called the "pomade".
The pomade is then washed or soaked with ethyl alcohol, which absorbs the fragrant components from the fat. The alcohol is allowed to evaporate, leaving behind the fragrant flower absolute. The fats used for the process are then used for making soap.
For hot enfleurage, the plant material is soaked in heated odorless fat. The fat is then filtered to remove the flowers and used again until it is considered to be saturated with fragrance.
Solvent extraction
Solvent extraction is the use of ethanol, hexane or other volatile compounds and mixtures for extracting aromatics from plant material. Flowers such as jasmine are soaked in the volatile solvent.
The solvent extracts the fragrant compounds from the jasmine. After the flowers are removed, the solvent is evaporated from the mixture. The remaining product is the absolute.
From the field: Jasmine Sambac in southern India
Robert Seidel, founder of The Essential Oil Company, described the jasmine harvest from a Jasmine Sambac plantation about an hour outside of Madurai, in southern India:
"Jasmine Sambac is the most important flower in this region, and it goes to the market for religious purposes, hair decorations, necklaces, things like that. It's harvested bright and early in the morning because at this time of day the buds are closed. They'll be harvested in the closed state because it maintains their fragrance. Once they go to the extractor, it takes about two hours and then the jasmine flowers open up, and they're very fragrant, and at that point is when they start the extraction. Jasmine is extracted using hexane as a solvent and you make jasmine concrete. The net result is jasmine absolute, which is very fragrant, and ends up in perfumes and foods across the world."
Gas extraction
Gas extraction uses CO₂ or other gases to extract volatile compounds. When a gas is placed under pressure, it becomes a liquid. This liquid is then used as a solvent to extract volatile components from dry plant matter. When the pressure is released the gas evaporates, leaving behind the gas extract. The gas is then re-compressed for further use.
Pressing
Pressing is used for extracting citrus essential oils. There are two types of presses.
One type of machinery scrapes the skin of the citrus fruit, which is where the essential oil is located. The thin scrapings are then washed with water, and the essential oil is separated from the mixture using a centrifuge. This type of extraction is used for bitter orange, where the juice is not extracted.
The second method is part of the citrus juice extraction process, and the essential oil is a by-product. Here the whole fruit is crushed. The resulting liquid contains juice, pulp and essential oil, which are then separated in a centrifuge.
Distillation
Distillation uses water and steam to extract essential oils from plants. There are three types of distilling used for essential oils: hydrodistillation, water/steam distillation and steam distillation.
Hydrodistillation
In hydrodistillation the plant material is soaked in water and the mixture is boiled. This is most commonly used for orange blossoms and rose petals. Hydrodistillation can be used for almost all plants.
Above: hydrodistillation of cananga flowers.
Water/steam distillation
In water/steam distillation the plant material in the retort does not sit in the boiling water but above it. The steam from the boiling water passes through the plant matter. Water/steam distillation is done under ambient pressure. This method is used for patchouli, clove leaf and citronella. It can also be used for almost all plants.
Above: water/steam distillation of geranium flowers.
Steam distillation
In steam distillation the steam is produced outside the distillation equipment, in a separate boiler. The steam then passes through the plant material under low pressure. This method is faster than hydrodistillation or water/steam distillation. We see it commonly with peppermint and lavender, and it can also be used with almost all plants.
Condenser and essencier
In all three methods, the steam containing the essential oil must go through a condenser. The condenser cools the steam back to a liquid state. The distillate is a mixture of essential oil and water. The water does not mix with the essential oil, but remains separate.
The distillate is then captured in an essencier (receiving can), where the essential oils and hydrosols are separated.
