A number of essential oils are obtained by steam distillation. Distillation is a separation process and in the case of essential oils involves separating oils from plant material by using heat which comes from steam. This is a gentle way of extracting oil, although may involve more heat than cold pressing. (Please see our page on cold pressing for more on this). In steam distillation the plants are not directly submerged in boiling water because at high temperatures the subtlest aromas might be altered.
Steam is passed at low pressure through a tank containing aromatic plants.
The steam moves through the organic material naturally capturing the volatile essential oil compounds that are released into the still as a vapour.
This vapour travels through a cold-water refrigerated pipe which condenses the steam into a liquid.
When the steam goes back into a liquid the oil will sit above the water because the oil molecules are lighter and so float to the top and water molecules are more attracted to each other than they are to oil so they do not combine. Occasionally an essential oil is heavier than water and is found on the bottom rather than the top, as with clove essential oil.
The essential oil and water can be easily separated. The remaining water, referred to as a hydrosol or floral water, is retained and sold separately.
Absolutes are highly concentrated aromatic substances and are obtained from delicate flowers by either enfleurage (which is almost obsolete) or solvent extraction. Absolutes often take a lot longer to come out of the bottle. Some people pre-warm their oil bottle in warm water.
Absolutes resemble the natural aroma of the plant and are normally more coloured and viscous than essential oils. Absolutes are used extensively in the cosmetic and perfume industries due to their strong aromas.
The solvent will pull out the essential oil from the plant, as well as the chlorophyll and other plant tissue, which produces a highly coloured or thick/viscous extract.
The first product made via solvent extraction is known as a concrete. A concrete is the concentrated extract that contains the waxes and/or fats as well as the odoriferous material from the plant.
The concrete is then mixed with alcohol, which serves to extract the aromatic principle of the material. The final product is known as an absolute.
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Tags: naissance, aromatherapy, essential oils, steam distilation, solvent extraction