From plant to essential oil
Essential oils are highly concentrated aromatic extracts that are distilled or expressed from a variety of aromatic plant material, including flowers, flowering tops, leaves, grasses, needles and twigs, fruits/zests, seeds, resins, roots, and woods.
It is very common in the massmarket today to refer to just about anything that is liquid in a brown bottleand smells as an essential oil. Even within the aromatherapy profession, manycall absolutes and CO2 extracts essential oils. Technically, however, onlydistilled or expressed substances are essential oils. The InternationalOrganization for Standardization (ISO) in their Vocabulary of Natural Materials(ISO/ D1S9235.2) defines an essential oil as a product made by distillation with either water or steam or bymechanical processing of citrus rinds or by dry distillation of naturalmaterials.Following the distillation, the essential oil is physically separated from thewater phase.
According to Dr. BrianLawrence “for an essential oil to be a true essentialoil, it must be isolated by physical means only. The physical methods used aredistillation (steam, steam/water and water) or expression (also known as coldpressing, a unique feature for citrus peel oils). There is one other method ofoil isolation specific to a very limited number of essential oil plants. Thisis a maceration/distillation. In the process, the plant material is maceratedin warm water to release the enzyme-bound essential oil. Examples of oilsproduced by maceration are onion, garlic, wintergreen, bitter almond, etc.”
Resins, such as frankincense,myrrh and benzoin are thick and sticky when extracted from the tree. Distilledfrankincense and myrrh are more liquid and benzoin stays thick.
Two methods of extractingessential oil:
- Steam Distillation: when essential oils and hydrosols are produced
- Expression: when citrus oils are produced.
The advantage of distillationis that the volatile components can be distilled at temperatures lower than theboiling points of their individual constituents and are easily separated fromthe condensed water.
Preparation of plant material:some plants require preparation prior to distillation. It is sometimesnecessary to crush, open, or in some other manner prepare the plant material inorder for the plant to release its essence during the distillation process.Roots, woods and seeds do need preparation. Woods are usually cut intoshorter lengths in order to expose the oil glands. The main purpose isto allow easier access to the volatile constituents as the steam passes throughthe material.
Plant material must bedistilled immediately after preparation and if it is not, two things mighthappen:
- The total amountof oil may be reduced
- Composition andaroma will be altered because some of the constituents will evaporate
These are the three types ofdistillation:
- Waterdistillation: this method is often used with flowers (rose and orange blossoms),the plant material comes in direct contact with the water. It is the ideal typeof distillation for flowers because direct steam causes these flowers to clump together.
- Water and steam:this method is used with herbs and leaves, the water remains below the plantmaterial, which has been placed on a grate while the steam is introduced fromoutside the main still.
- Steam distillation:it is the most commonly used method, steam is injected in the still, usually atslightly higher pressures and temperatures than the above methods.
Hydrosols: a co-product of distillation, whichcontains a small amount of essential oil components. Every liter of hydrosolcontains between 0.05 and 0.02 milliliter of dissolved essential oil.
Extraction is a method used for citrus essential oils: tangerine, lemon, bergamot, sweet orange and lime. Most modern expression techniques are accomplished by using machines using centrifugal force. The spinning in a centrifuge separates most of the essential oil from the fruit juice.
Written by Lena Isayev, B.A., C.A.