Extraction Methods for Essential Oils
There are many ways to extract a plant's fragrant and therapeutic parts. This can sometimes depend on the plant material and how fragile it is or on which elements we want removed. These are the most common ways to do it.
Steam distillation
This is the most common way of extracting essential oils. The plant material is in direct contact with water or steam, then the evaporated oil condenses by passing through cooling tubes, and the resulting oil is collected. This process will sometimes result in floral water or hydrosols, like in the case of rosemary or peppermint, among a few others.
Cold Expression
This method is usually reserved for citrus fruits, where the essential oil glands are on the surface of the outer skin. The fruit is put through a machine that marks the tissue and releases the oils. Water is then added to separate them out. The resulting oil can sometimes contain some of the non-volatile components of the oil, like Furanocoumarins, which are responsible for some citrus oils being phototoxic. These elements can be removed further to produce non-photo toxic oils (FCF-free).
Absolute Extraction
Some plants are too delicate for steam distillation. Absolute extraction involves putting the plant material inside a solvent (like hexane) to dissolve the aromatic molecules. The result is concrete or a floral wax, which then gets washed out and an absolute product results. The absolute will usually contain some of the heavier non-volatile molecules of the plant as well as trace amounts of the solvent used and will have a strong fragrant scent.
Co2 Extraction
Due to the high initial set-up cost, this method was usually reserved for the perfume and food industry until recently. Co2 extraction uses carbon dioxide in its compressed liquid form to extract the aromatic molecules and some heavier non-volatile elements. The amount of pressure and heat used can be adjusted to extract different components of the plant. The resulting oil scent is much closer to the living plant and has uses that can differ from the essential oil from the same source.
Enfleurage
One of the oldest methods of extracting scent from flowers that are too delicate for steam distillation. By placing the fresh fragrant petals on a layer of fat (traditionally lard) and replacing the petals with new ones over time. The fat will take on the fragrance of the flowers. This method is very time-consuming and requires a lot of manual labour and efficiency in replacing the fresh petals. Still, the result is usually a delightful product.
Infusion
Placing fresh or dried plant material in a carrier plant oil (like olive oil) and infusing it with heat or sunshine over some time until it takes on the scent and properties of the plant material soaking in it.
The method is straightforward but takes patience and some experience to get the resulting oil to be both fragrant and beneficial.
Floral Wax
The result of dissolving plant material in a solvent. It contains the wax and heavier material of the plant and a percentage of the essential oils. It usually has a powerful scent and can be used in cosmetic and perfumery products.
Resinoids
Solvents extract oil from solid tree resins in a way very similar to how absolutes are extracted. Resins can dissolve in alcohol but not oils. They are often very thick in consistency.
Oleoresins
Similar to Resinoids, except they contain both the essential oils and the resin solids. They will dissolve in water but not oil or other essential oils.
Hydrosols
They are usually the water left over from the steam distillation of the plant material and will contain trace amounts of the essential oil itself. In some cases, artisanal distillers will specifically process a plant to extract its hydrosol, with the essential oil being the by-product.
Certain factors remain constant regardless of the process used to produce a bottle of essential oil. The health and quality of the plant used and the soil and environment it grows in can significantly affect the result and its potential for effective use. Knowing the source of your material and being mindful of the work and effort that goes into each drop used in a blend is a step in addressing the sustainability of these precious resources.
