Aromatherapy & Aromacology
Extracting Essential Oils
The only methods of extracting essential oils are through steam distillation and expression. Methods of extracting plant oils include use of volatile solvents and dissolving. The choice of method is important for it will influence the ultimate quality and therapeutic value of the oil. Indeed, each method of extraction gives a different product, as each process extracts dif¬ferent constituents from the plant. I am concerned that as extraction methods become more sophisticated and mechanized, so new constituents which might alter the therapeutic balance of the oil may be extracted. They may be beneficial, but they may not: there is a huge amount of research that needs to be done into the vast subject of essential oils.
Whichever method is chosen, the extraction of essential oils is a painstaking process as the amount of oil present in plants is minute. So, huge quantities of plants are needed for viable amounts of oil: 200 kg (440 lb) of fresh lavender flowers, between 2 and 5 metric tonnes of rose petals and 3,000 lemons are needed to produce 1 kg (2 1/4 lb) of essential oils of lavender, rose and lemon respectively. This is what makes the essential oils so expensive, and why some producers are turning to more economical methods of extraction using volatile solvents and thereby cutting into the heart of the therapy. As oils extracted this way are in effect adulterated and not the pure essential oils, they should not be used for aromatherapy. Oils extracted by volatile solvents are intended for the fragrance industries, which carry their own restrictions. Steam Distillation
This has been used as a method of extracting essential oils from plant material for thousands of years. The Ancient Egyptians are known to have placed their raw material and some water in a large clay pot. Heat was applied and the steam that formed had to pass through layers of cotton or linen cloth placed in the neck before escaping. The essential oils were trapped in this material, and all that had to be done to obtain them was to squeeze out the cloth occasionally. This is the basic method still used today, although a little more refined.
In the distillation of Australian tea tree oil, for instance, a common bush-still consists of a 1,600-litre (115-gallon) capacity tank with a removable or hinged lid capable of being sealed to make the container steam-tight. A grid is fitted in the tank about 30 cm (1 ft) above the bottom to support the closely packed leaf (called the charge) and allow an even passage of steam through it. If steam is generated in the still itself (sometimes it is supplied by a separate boiler or steam generator), a constant level of water is maintained in the bottom and a fire built underneath it. An outlet at the top of the still carries the mixture of steam and oil vapour to the condenser, where the steam condenses back to water, and the oil vapour condenses as well. Because they are not water soluble, the oils separate and collect on the surface of the water when cool, and can be collected quite easily. That 1,600-1itre tank holds half a metric tonne of fresh leaves, takes two to three hours to distil, and yields 7-10 kg (15-22lb) of oil. Extraction by Volatile Solvents
The process is similar to steam distillation, with the basic material placed in racks in a huge tank like a pressure cooker. Volatile solvents are heated and allowed to flow through the racks. The solvents, when saturated with the plant essentials, are evaporated off, leaving certain odiferous molecules and constituents behind, together with some chemical residue. It is a process which many producers and the perfume industry favour because its return in terms of fragrance is so very much higher than that of steam distillation, and with rose, for example, the fragrance obtained is actually stronger. The product extracted by this method is not essential oil, but what is known as a concrete. A concrete should never be used in therapy, since it not only contains chemical residue from the solvents, but because the balance of constituents extracted by the solvents is different to those extracted by steam distillation.
Benzene used to be one of the solvents used in the extraction of essential oils to obtain a concrete, but it is now used less and less as it leaves a residue behind that is known to cause allergies. Legislation has actually recommended that the traces left should be under 10 parts per 1,000. There are also formal restrictions for its use in the perfume industry due to its toxicity for the workers that handle it. The effects of its toxicity have been recognized by distilleries in Grasse as an industrial illness Hexane and chlorure of methylene are other extraction solvents which are even more volatile than benzene. It is estimated that 700 tonnes of chemicals per year disperse in the air around Grasse alone.