Essential oils are often open to adulteration in aromatherapy use; in addition, there is the use of fragrance oils and hydrosols in general ‘aromatherapy’ use, although therapeutically different in their use to essential oils (if at all). The chemistry of an essential oil is complex and, depending from which plant it was extracted or distilled from, the properties of an essential oil can vary.
Furthermore, some plant material is used to produce essential oils and other substances such as concretes, absolutes, resins, resinoids and oleoresins; some plants are capable of producing the material for one or more of these substances, some not. Therefore, it is not surprising to have difficulty in deciding if an essential oil really is an essential oil.
What is an Essential Oil?
Essential oils are obtained through a process of extraction or steam distillation of the various parts of a plant; essential oils may be obtained from the roots, flowers, leaves, seeds and bark of a plant. A pure essential oil will be obtained from a single species and not be ‘adulterated’ with other botanical species. It is the ‘aroma’ of the plant (from tiny glands, sacs and hairs) which is captured in an essential oil and used therapeutically in aromatherapy.
Solvent Extraction : Concretes and Absolutes
Some plants are used to produce concretes and absolutes; concretes and absolutes are not essential oils, although some plant material can be used to produce both essential oils and concretes and absolutes. Due to methods of production, concretes and absolutes are not ‘pure’ like essential oils and therefore do not hold the same therapeutic properties.
Concretes are prepared from plant material by the use of a hydrocarbon solvent to produce a waxy, solid substance which is widely used in the perfumery industry; absolutes are prepared from a concrete by alcohol extraction and are again of much use to the perfumery industry.
Resins, Resinoids and Oleoresins
Resins are the natural material (a gum substance) exuded from the bark of a tree when it is cut; resinoids are the result of a resin extraction, by use of a hydrocarbon solvent. Absolute resins are also produced using an alcohol solvent. Oleoresins are the natural material exuded from plants and extracted using a solvent; oleoresins produce an end result of essential oils and resins (and solvents).
Plants Which Produce Concretes and Absolutes
Examples of plants which produce concretes and absolutes include:
- Mimosa (Acacia dealbata)
- Cassie (Acacia farnesiana)
- Marigold (Calendula officinalis) – absolute
- Tonka (Dipteryx odorata)
- Oakmoss (Evernia prunastri)
- Gardenia (Gardenia jasminoides)
- Jasmine (Jasminum officinale) – note, an ‘essential oil’ is steam distilled from the absolute, and not the plant, resulting in Jasmine absolute and not Jasmine essential oil, as many believe
- Melilotus (Melilotus officinalis)
- Narcissus (Narcissus poeticus)
- Linden (Tilia x vulgaris)
- Violet (Viola odorata).
Plants Which Produce Resinoids and Oleoresins
Examples of plants which produce resinoids and oleoresins include:
- Deertongue (Carphephorus odoratissimus) -oleoresin
- Opopanax (Commiphora erythraea) – resinoid in addition to an essential oil
- Myrrh (Commiphora myrrha) – resinoid in addition to an essential oil
- Nutmeg (Myristica fragrans) – oleoresin (from mace) in addition to an essential oil
- Patchouli (Pogostemon cablin) – resinoid in addition to an essential oil
- Benzoin (Styrax benzoin) – resinoid (or resin absolute)
- Vanilla (Vanilla planifolia) – resinoid.
Pure Essential Oil or Solvent Extraction?
In aromatherapy, pure essential oils are primarily used for therapeutic use; a plant material which has been solvently extracted will not be ‘pure’ and will not hold the same therapeutic powers of a pure essential oil. However, concretes and absolutes have a place in the perfumery world and resinoids and oleoresins have uses too.
It is important to identify which plants are capable of producing essential oils, concretes, absolutes, resins, resinoids and oleoresins; some plants can be extracted to produce all of these substances, some only produce an essential oil, and some only produce concretes and/or absolutes or resinoids.