Essential Oil Production
Essential Oil distilleries have classically used hydrodiffusion (steam distillation) to produce Essential Oils. During distillation, steam runs through the plant material. The hot steam breaks down the cells of the plant and carries the essential oils to a cooling chamber where the hydrosol (water portion of the plant) and the essential oil (volatile oils of the plant) are then separated. Notice the separation of essential oil (top) and hydrosol (bottom) in the image of fresh lavender distillate to the left. This image was taken at the California School of Herbal Studies during an essential oil distillation class.
Like fine wines, the end result is dependent upon several factors which include: growing methods (preferably Organically grown, Bio-dynamically grown, or Ethically wildcrafted), geography, climate, soil conditions, and most importantly, the technique and expertise of the distiller. The amount of essential oil that each distillation yields is dependent upon the plant. Price is usually a reliable indicator of how much oil each crop yields. For example, it takes approximately 30 rose buds to produce a single drop of rose otto essential oil. 1 ml (approximately 30 drops) then, is sold for about $35 on the retail market. Lavender, on the other hand, yields approximately 4 liters of oil per ton of plant. A 5 ml (1/6 of an ounce) bottle of true lavender is found for about $10-$15.
A relatively new method of extraction that is being employed is called carbon dioxide extraction, or CO2. This process utilizes the "supercritical" state of CO2, when it acts both as a gas and a
liquid. The required equipment used for this method is quite expensive but yields a higher volume of essential oil, making more expensive oils such as frankincense and myrrh more widely available. CO2 extraction, which is cooler than steam distillation, is also gentle on the plant material and yields essential oils with exceptionally true aromas.
Most high quality citrus essential oils are obtained from a cold pressing of the rind or peel. This process is often called scarification. As in steam distillation, to insure high quality essential oils it is necessary to use only the finest plants available. The common use of chemical pesticides in industrial citrus farming makes using organic citrus essential oils especially important. Many citrus essential oils on the market are bulk essential oils of inferior quality made by steam distillation of the peels rather than scarification.
Another method used to extract essential oils from plants is by using solvents. These oils are called absolutes. Absolutes are commonly used to extract the essence from very delicate plant parts like flower petals. Common absolutes are Rose, Jasmine and Mimosa. These are used primarily for perfumery and blending, and because of the solvents used in extraction, are not considered to be a therapeutic grade.
Most flowers contain very little volatile oil to undergo expression and their chemical components are too delicate and easily denatured by the high heat used in steam distillation. Instead, a solvent such as hexane or supercritical carbon dioxide is used to extract the oils. Extracts from hexane and other hydrophobic solvent are called concretes, which is mixture of essential oil, waxes, resins, and other lipophilic (oil soluble) plant material.
Although highly fragrant, concretes contain large quantities of non-fragrant waxes and resins. As such another solvent, often ethyl alcohol, which only dissolves the fragrant low-molecular weight compounds is used to extract the fragrant oil from the concrete. The alcohol is removed by a second distillation, leaving behind the absolute.
In supercritical fluid extraction, supercritical carbon dioxide is used as a solvent. This method has many benefits, including avoiding petrochemical residues in the product. It does not obtain an absolute directly. The supercritical carbon dioxide will extract both the waxes and the essential oils that make up the concrete. Subsequent processing with liquid carbon dioxide, achieved in the same extractor by merely lowering the extraction temperature, will separate the waxes from the essential oils. This lower temperature process prevents the decomposition and denaturing of compounds and provides for a superior product. When the extraction is complete, the pressure is reduced to ambient and the carbon dioxide reverts back to a gas, leaving no residue. Although supercritical carbon dioxide is also used for making decaffeinated coffee, the actual process is different
