Essential oils are made from the parts of plants that give them their aroma. Plants use these oils to attract pollinators, to ward off predators, to oxygenate themselves and to increase their immunity to disease. Essential oils can come from any part of a plant: the leaves, flowers, bark, roots or fruit. Pure essential oils contain only these aromatic oils and can be quite expensive to make because a pound of essential oil can require several tons of plant material. There are three main ways that essential oils are made.
Solvent Extraction
Solvent extraction is the simplest approach to making essential oils. Plant material is soaked in a solvent to draw out the scent. Then, the plants are removed from the solvent and the scented solvent is bottled. Solvent extraction is the method you would most likely use to make essential oils at home with wild-crafted plants or plants from your garden.
The most common solvents are carrier oils like sunflower, olive or sweet almond oil. Other solvents include hexane or pure ethyl alcohol. Some essential oils are extracted with carbon dioxide, where the plant material is heated in a pressure chamber with hypercritical carbon dioxide. Hypercritical means the carbon dioxide is in a both solid and gaseous state. Extraction is fast with this method, and the resulting oil is the purest.
A more work-intensive method of solvent extraction is called enfleurage, where plant matter is left to soak in a carrier oil until all of the aroma is removed, then the spent plants are replaced with fresh ones until the carrier oil is saturated. This carrier oil may be used as essential oil, or it may be separated further by mixing it with alcohol to separate the carrier oil from the essential oil.
Distillation
Some essential oils are made in stills with a process of distillation. In the water distillation process, the plant material is boiled in water. The condensation is collected and cooled, and the oil is separated from the water. Water left over from this process is often sold as floral water, like rosewater or lavender water. Steam distillation is similar, where steam is forced over plant material to extract the oils, which are then collected from the condensation.
Expression
Expression, also called cold-pressing, is the method used to extract carrier oils like nut oils and high- quality olive oil. It is also most commonly used to extract citrus oils from the rinds of citrus fruits. In the expression process, the plant material is placed in a machine that uses high pressure to squeeze the oils out.
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