PRODUCTION METHOD OF ESSENTIAL OILS
There are many methods to extract the aromatic qualities from plants. Teas, tinctures, decoctions, infused oils, herbal beers, and wines all extract and concentrate the volatile components of the plants, but these are not essential oils. Essential oils are much more concentrated and are produced by steam distillation, cold pressing, CO2 hyperbaric extraction, and solvent extraction. Each method has advantages and disadvantages and produces a different oil quality. Steam distillation is the most common method of essential oil extraction.
Distillation uses the extraction abilities of steam, and sometimes pressure, to pull the plant material is placed on screens over boiling water, or super-heated steam from another source is piped through the plant material. As the steam passes through the plant material, the volatile components are lifted, condensed in a cooling coil, and precipitate out as a combination of distilled water and volatile components. The mixture is collected in a florentine vase (which has an hourglass shape). In most cases, the distilled water is heavier and sinks to the bottom, while the essential oils, being lighter, rise to the top, at which point a valve can be opened and the essential oils drained off.
There are very primitive methods of steam distillation that use very low heat and may take as long as a month to distil one batch of essential oils. The advantage of ‘slow’ distillation is that the long time (and patience) allow some of the larger molecules to be gently coaxed out and can produce an essence that has a broader range of smells. More modern distillation methods may use higher temperatures to very quickly extract essential oils, sometimes in minutes. This method can produce oils quickly, cheaply and efficiently; however, the bouquet, or range of smells, is somewhat restricted by this method and involves a loss in some of the possible therapeutic qualities.
Cold pressing is the second most common method of essential oil production. It is most helpful in processing citrus rinds such as lemon, orange, grapefruit, tangerine, bergamot and mandarin. The rinds, or in some cases the whole fruit, are chopped or ground and pressed to extract the essential oil components found in the fruit’s skin. In the early days, and some places in the world today, the rinds of these fruits were squeezed into sponges. Take a piece of citrus rind, fold it, skin it out, and notice the spray of essential oils (watch your eyes). Do this into a candle flame and witness the flash of blue as the volatiles ignite.
Cold pressing produces a combination of essential oils and watery components that can be separated from the essential components collected. This process’s mechanical nature produces essential oils that are not as pure and tend to oxidize or lose their potency if left unrefrigerated for more than two years. On the other hand, the steam-distilled essential oil will grow richer in smell over the years and, in some cases, have an unlimited shelf life.
The CO2 hyperbaric production method utilizes as much as 22 atmospheric pressure in the presence of pure CO2 gas (the same pressure found at ocean depths of 660 feet). At high pressure, the CO2 becomes liquid and has the ability to extract essential oil components from the plant material. This liquid is drained off and allowed to depressurize, at which point the CO2 becomes a harmless gas. What’s left in the bottom of the chamber is pure essential oil. This method benefits lighter fragrances, such as tuberose or jasmine, where the flowers have light, easily lost aromatic components. The cost of the compression equipment is excellent, and the oils produced are more expensive than steam distilled.
The solvent extraction method is also helpful with light aromatic flowers. The flowers are collected, and a solvent such as hexane or ether is poured over them. The solvents are evaporated using a vacuum, and what’s left is a very thick, sticky residue known as a ‘concrete’. The concrete can be dissolved in alcohol, the alcohol pulled off, and the remaining essential oil be known as an ‘absolute’. Perfumers like this method because it doesn’t involve heat, pressure, or mechanical pressing, which can change the odour of the flowers. Perfumers maintain that absolutes are more faithful to the original smell of the flower than oils produced using any other production method. Aromatherapists, however, know that a small amount of petroleum solvent always remains and can harm the human immune system, causing reactions in sensitive people. In aromatherapy, it is the method least preferred, and oils produced in this manner are never used internally.