28 May 2009

Essential Oil Extraction

It is pretty common in the bath and body products industry to go natural these days. One of the ways that companies have found successful is to eschew fragrances and perfumes, which are, by and large, synthetic and opt instead for essential oils. This results in not only a more natural end-product, but one that is often more delicately scented. However, before we can use essential oils in soaps, lotions, perfumes or other cosmetics, we have to extract them from the source plant, whether it be lavender, chamomile or vanilla. The extraction method has an effect on the essential oil - it can change it, or even contaminate it, in which case the claim of natural cannot be maintained.

There are a number of ways in which essential oils can be extracted. All, except expression are solvent based, however we will separate them out, and refer to the solvent method as using something unnatural, resulting in solvent residue.

Distillation refers to water or steam distillation. The base plant material is permeated with water and essentially boiled at 100 degrees C. Similarly in steam distillation, steam is injected, often under pressure to separate the essential oil from the plant material. This happens at temperatures above 100 degrees C. Because of this, constituents in the essential oils can often decompose into oxidative products. However, this process is considered to be natural and the yield is high, little is wasted.

Expression is often referred to as 'cold pressed'. Olive, coconut and avocado oils are often cold pressed. No heat is used, so volatile constituents remain unchanged. Yield can be low though, so this is often not a very efficient or cost effective method. There are several methods of expression that we won't go into here, but citrus oils are uniquely suited for this extraction method.

Supercritical CO2 is carbon dioxide above 31 degrees C and under extreme pressure (>72.9 atmospheres) that is used as a solvent. The supercritical CO2 bonds with the essential oil constituents in the plant material and extracts them. When the pressure is removed, the CO2 simply evaporates, leaving the pure essential oil. Since no heat is employed, the essential oil is unrefined and in its natural state. Often the scent, potency and crispness of the essential oil are enhanced as compared to steam and water distillates, scenting more closely to the original plant. While more expensive, the essential oil often goes further. The oils produced by this method are, like those extracted through expression, the purest and most natural.

Solvent extraction for our purposes here is where an organic, but not necessarily natural, solvent such as alcohol, petroleum ether or hexane (among others) is used. Often used because of cost effectiveness, it is also used for very delicate essential oils or where the essential oils are found in very minute quantities, such as rose or jasmine. This type of extraction produces a waxy substance called concrete. This concrete is then heated and dissolved into alcohol. This is then distilled in a vacuum, resulting in an absolute. Absolutes are generally very expensive. The problem for the natural community is that after extraction, quantities of the solvent may remain, often in large percentages. Hexane extraction leaves 8-10 ppm of hexane (a petrochemical) in the essential oil. This method is not viewed in the natural community as being natural and is avoided by those companies that are truly committed to natural products.

It is important to know the extraction method of an essential oil to determine not only its quality but if it can still be considered a natural product. Essential oils on an ingredient list do not guarantee natural and are often used in greenwashing exercises. The good news is that the demand for really natural products by consumers has opened up essential oils to serious scrutiny.

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