There are different ways of extracting the essential oils, or scents, from plant matter and I will explain the methods in this post. Some oils can be extracted through different methods and give EO’s different in scent: Rose, for example, is both distilled; Rose Otto, and solvent extracted; Rose absolute, giving very different scents. Jasmine can be both solvent extracted; Jasmine absolute, and extracted through enfleurage; Jasmine enfleurage, but it can’t be steam distilled.
STEAMDISTILLATION: The most commonly used method. Steam is passed through the plant matter, “popping” the essential oil cells in the plant, carrying the light-weight EO with it into a cooler where the steam returns to water and the essential oil separates from the water. This is then collected in a vessel where water and essential oil will separate since EO’s don’t mix with water. Depending on the density of the EO, it will either sink to the bottom or stay on top of the water. The EO is then taken out and bottled while the water is either used again or bottled as a hydrolat. The steam will only carry molecules that are light-weight enough, leaving behind waxes and other heavier plant-matter. Other light-weight molecules that are water-soluble will be carried by the steam and stay in the resulting water, hydrolat, which also contains tiny amounts of EO.
SOLVENT EXTRACTION (absolute, concrete, resinoid):This method is used mainly for very fragile materials such as flowers (jasmine, tuberose), or to extract scents for perfumery, as absolutes tend to be more true in scent to the real thing. The plant matter is mixed with a solvent, usually hexane, in which essential oil, waxes and colour is extracted from the plant matter. The solvent is then distilled off, leaving a waxy, semi-solid substance called concréte which consists of essential oil and other plant substances such as natural waxes. The concréte is then mixed with alcohol and filtered from all substances but the aromatic material. After evaporating the alcohol, there is an absolute.
COLD EXPRESSION: This method is used for all citrus oils, where the essential oil is found in the rind of the fruit. There are two different methods: The sponge method: The rind and pith is removed from the fruit and soaked in warm water to become more pliable. It was then inverted to break the cells that hold the essential oil. The EO is collected by sponges which are then squeezed to release the liquid. Water and EO separates. Écuelle à picquer: The citrus is placed in a rotating device with needles that break the EO cells, the oil and water-based material run off through a funnel, the oil is separated from the water and bottled.
CO2 EXTRACTION: Hypercritical carbon dioxide gas extraction. CO2 is the gas we breath out and the gas that plants thrive on. Carbon dioxide becomes hypercritical when a certain amount of pressure is applied, which means that the gas is turned into a liquid. This liquid can be used as a safe solvent for extracting EO’s from plant matter. CO2 is inert and doesn’t interact with the essence that is being extracted, furthermore there is no thermal degradation of the essence, since heat is not being applied. To remove the CO2, all that is needed is to remove the pressure, turning the liquid into gas, which can be used again, leaving only the EO. To obtain EO’s, relatively low atmospheric pressure is needed, extracting only the volatile parts of the plant. When higher atmospheric pressure is used, “heavier” plant materials are extracted as well (waxes, resins), leaving a substance much like the absolutes but without any traces of solvents.
ENFLEURAGE: A very old, time-consuming method which is hardly ever used today. The only oil I have come across that is extracted this way is a lovely Jasmine. There is not much of it around and it is very costly. Cold enfleurage: Odorless fat that is solid at room-temperature (usually deodorized tallow or lard) is smeared onto framed glass-plates, called “chassis“, upon which the flower petals are spread in a single layer. The scent is then absorbed by the fat. Once the petals are depleted, they are removed and new petals are spread onto the fat. This is repeated until the fat is saturated with scent, it is then called a pomade. The pomade is mixed with alcohol, drawing the scent into the alcohol. The fat and alcohol is then separated and when the alcohol evaporates it leaves the absolute. Hot enfleurage:Petals are stirred into deodorized fat and heated. Again, depleted petals are strained and new added until the saturation is complete. The rest of the process is the same as in cold enfleurage. The remaining fat is used for soap as it is still scented. If you have read or seen “The Perfumer”, this is the method he used to extract the scent of woman 🙂