Medicinal and aromatic plants have species specific chemical components that give them their unique properties. These are the “active ingredients” if you will. Modern medication is made up of active ingredients which have been mixed with other stuff so that it can be made into a readily ingested and absorbed form allowing the active ingredient to have the desired effect. Plants are not just active ingredients, there is a lot of plant material containing the active ingredients. The plant oils, or essential oils, tend to accumulate in greater concentrations in different parts of the plant; such as the flowers (rose, lavender, jasmine); leaves (mint, lemongrass); stems (geranium, patchouli); bark (cinnamon, cassia); wood (sandalwood, cedar); resin (myrrh, frankincense); roots (angelica, vetiver); rhizomes (ginger, calamus); fruit (orange, juniper); or seeds (fennel, coriander). The essential oils are the concentrated active ingredients of the plant and there are several different ways in which these essential oils can be extracted from plants.
Technically, true essential oils are extracted through mechanical means or distillation – using either water, steam, or a combination or recombination of the two. Aromatic plant oils extracted through other means can be called concretes, absolutes, resinoids or pomades, depending on the technique used to extract the oils. In biblical times, the most likely methods of extracting plant oils were distillation or expression . This means that true essential oils have been in use for longer than we have historical records for. Olive oil was an oil of enormous economic and cultural importance and has been extracted through cold pressing for millennia. The Egyptians used distillation and expression for the oils used in embalming rituals. The following is a brief description of the most commonly used methods of extraction.
Distillation is the most commonly used extraction method and may be one of the oldest. There are records of distillation being used by Arabs 3000BC but the technique may have been discovered as far back as the Indus Culture about 5000 years ago . Distillation involves passing either water or steam through the plant material. The heat of the water or steam releases the phytols from the plant cells and they are carried into the collection section of the apparatus. The essential oils do not mix with water, and so they are siphoned off the water (which is then known as a hydrosol or floral water).
Expression is a mechanical extraction technique also known as cold pressing – basically squeezing the essential oils out. In order to get all the essential oils possible, it is rinsed with water and then the essential oils (which do not mix in water because it is a different weight) are separated out. This technique was certainly used in ancient Egypt to extract citrus oils. Due to the fairly simple technique (if you’ve ever been misted by an orange while peeling it, you will know how simple it is), it is likely that this method has been around for longer than distillation has.
CO2 extraction is similar to distillation, except that instead of water, highly pressurised liquid carbon dioxide is passed through the plant matter. The carbon dioxide turns into a gas at a much lower temperature than the essential oils, and so evaporates leaving only the essential oils.
Enfluerage is an old, costly, and mostly redundant form of extraction, which makes use of a layer of fat or wax (known as a chassis) onto which the plant material is placed. The oils diffuse into the fat or wax and, once the plant material has been replaced a number of times, the essential oils are separated from the chassis using alcohol. Once the alcohol has evaporated we are left with the essential oils known as an absolute.
Some plants have higher concentrations than others. For example, when peeling an orange, you will often get stains on your fingers from the essential oils in the peels. However, jasmine flowers are a completely different story – for one drop of essential oil, about 190 jasmine flowers are needed. This also explains why some essential oils are more expensive than others – not because they are more effective, but because they are scarcer.
- Gordon-Conwell Theological Seminary, “Cultural and Historical: Perfumes and Anointing Oils,” in Archaeological Study Bible, Michigan, Zondervan, 2005, p. 1746.
- E. Schmidt, “5. Production of Essential Oils,” in Handbook of Essential Oils: Science, Technology, and Applications, 2nd edition, London, CRC Press Taylor & Francis Group, 2016, pp. 127-162.