An essential oil is a concentrated liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from an assortment of tree's, flowers and fruits. Essential oils are the oil of the plant from which they were extracted, such as lavender essential oil. An essential oil is the "essence of" the plant's fragrance—the unique fragrance of the plant.
Essential oils are most often extracted by distillation.
Essential Oils are not synthetically manufactured in labs, essential oils are extracted from plants through specific removal methods. Steam distillation is the most common way to extract aromatics (essential oil) from a plant. A large container called a Still containing the plant material has steam added to it. During the steam distillation process, steam is injected through the plant material containing the oils. As the steam flows through a condenser and cools, it has a layer of oil and a layer of water. The essential oil rises to the top and is separated from the floral water and collected.
Other extraction methods include expression which is most commonly used for fruit. This method involves the rind of the fruit, or peel. This method does not require heat, so it is often referred to as “cold pressing.” The fruit is placed in the expression machine where it is passed across graters that cut up the peel. During this process the essential oils break open and release their contents. Water is sprayed over the fruit to collect the essential oil. To remove the essential oil, the mixture is filtered allowing separation of the essential oils from any water or solids from the plant.
Another method is solvent extraction. This method produces "Absolutes" witch differ from true Essential oils because they can contain both aromatic and chemicals . Solvent extraction process is another form of cold processing method, it used with flowers that are too delicate for the steam distillation. The solvent dissolves all fragrant compounds from the plants. The solution containing both solvent and plant material is filtered and then put through a low pressure distillation to recover the solvent for further use. The remaining waxy mass is called concrete. Concretes contain all of the concentrated fragrant compounds of the plant as well as waxes and plant material. The concrete is processed with a second solvent. The oil is soluble in this solvent but the other materials are not. As a final step the purified solution is cold filtered leaving the absolute oil. A small amount of solvent will remain in the Absolute oil. Absolute extraction is not considered a “preferred method” for extracting essential oils but it is necessary for some plants. Absolutes are mostly used in oils that are put into perfumes.
Resin tapping is also a form of extraction for tree's. As you might guess this is the same extraction method as used for extracting the Famous Canadian "Maple Syrup". Resins are sticky, liquid, organic substances that usually harden when exposed to air. Most resins are harvested by a process known as tapping, a fairly labor intensive process. Resin is usually collected by causing minor damage to the tree by making a hole far enough into the trunk to to let sap exit the tree. The tree repairs its damage by filling the hole with resin, this can take a few days. The tap remains in the tree to collect the remaining resin runoff. Once the resin hardens, it is collected and steam distilled to extract the essential oil.
C02 Extraction is a fairly new process that is not used as often. Steam distillation is typically considered the best way to obtain essential oils for use in aromatherapy - because CO2 extracts were not available until recently. C02 extraction produces a better extract. When pressure is applied to C02, it produces a liquid solvent. (Plants live on C02 - photosynthesis is when the plants use the sunlight to breakdown the C02 & water into sugar and oxygen which gets released at night). The difference between C02 extraction and distillation is that C02 is used as a "solvent" instead of steam. Another difference between C02 extracts and distilled essential oils is that C02 extracts can contain more essence found in the plant than just the essential oil. CO2 can be totally removed which produces a purer oil than other methods.
The Florasol extraction method. This extraction method uses a new type of gas solvents. The solvents are used for the extraction of aromatic oils and other components from plants. Extraction occurs at or below ambient temperatures, so there is no degradation of the materials. The extraction process uses the solvent and produces a clean oil free of waxes.
There are a few other types of extraction, but the ones above are the more commonly used.