Essential Oils Library: Metamorphosis


Essential oils are obtained from the specific plant matter in which they reside.  “Long gone are the days when oil was produced at home in very slow, mallet-hammered, manually-operated wedge presses. Seeds were poured into a wedge-shaped container, and a wooden wedge was driven into it. Every hour or so, the housewife would hit the wedge with a wooden mallet, and the oil would drip for about an hour. Then she would give it another whack repeating the process again. She would carry this on all day, to produce the oil needed for her household.”1

“With the exception of consuming fresh or dried plants, a traditional method of herb use was aqueous extraction and preparation of herbal soup or tea.” Water extraction is probably the simplest and cheapest method of removing essential oils, but the quality of the oil has the greatest potential to be modified due to the effects of direct heating and contact with water.  The water extracted oils are commonly darker in color and have stronger still ‘off-note’ odors than oils produced by the other methods, and therefore tend to be of the lowest value.”2 In the water extraction method, the chopped plant matter is submerged directly in boiling water. Water acts as a solvent that extracts carbohydrates, peptides, glycosides, and tannins. Leaves and flowers are usually steeped, and roots and barks are usually decocted (simmered). Unfortunately, water extracts are susceptible to fermentation, which limits their longevity. Arabic medicine included the discovery of distillation,”3 “Ibn Sina, a great physician of the age, known in Europe as Avicenna (circa 1000 AC), invented a pipe which steam distilled the plants and produced true essential oils and not aromatic waters as in the past.”4 The Bundjalung Aborigines, who live North of New South Wales have been crushing the leaves of the Tea Tree to release the oils, and then soaking them in water to use in compress or infusions.

Today, Water Extraction, Cold Pressing, Steam/Dry Distillation and Solvent Extraction are the main large scale methods used to remove precious oils from plants.

Cold expression is the oldest of the “modern” methods of extracting essential oils.  This extraction, without the use of extraneous heat was in practice long before distillation. The main reason for this was due to the fact that the needed tools such as stones or simple wooden tools were readily available. The main oil extracted in this manner is citrus, which includes orange, tangerine, grapefruit, lemon, mandarin and others. Today countries vary by what can be labeled as cold-pressed. “In Switzerland, 'cold-pressed' is defined to mean that oils have reached temperatures not exceeding 50°C (122°F) during their entire journey from seed to bottle. In North America, there is no such agreed-upon definition.  The temperature of oil that drips out of huge presses may be between 85 and 95°C (185 to 203°F). Inside the press, the temperature is somewhat higher due to the delicate nature of the skin and the instability of the aldehydes in them cold expression is the primary means of removing the essential oil from citrus. In this process oil glands within the peels of citrus fruits are crushed to release their content.5 Lime is the one citrus fruit that can be cold pressed or distilled.  Citrus oil production is now a major by-product process of the juice industry”6

Steam distillation is without a doubt the most frequently used method for extraction of these precious oils from plants. “To extract the essential oil, by steam distillation the plant material is placed into a still (very similar to a pressure cooker) where pressurized steam passes through the plant material. The heat from the steam causes globules of oil in the plant to burst free from the cells walls due to the increasing pressure and the oil then evaporates. The essential oil vapor and the steam then pass out the top of the still into a water cooled pipe where the vapors are condensed back to liquids. At this point, the essential oil separates from the water and floats to the top.”7 The advantages and disadvantages of steam distillation are as follows:

  • The amount of steam and the quality of the steam can be controlled.
  • Lower risk of thermal degradation as temperature generally not above 100 °C.
  • Most widely used process for the extraction of essential oils on a large scale.
  • Throughout the flavor and fragrance supply industry it is the standard method of extraction.
  • There is a much higher capital requirement and with low-priced oils the pay back period can be over 10 years.
  • Requires higher level of technical skill and fabrication and repairs and maintenance require a higher level of skill.”9

The type and variety of Steam Distillation plants vary greatly all over the world. This ranges from the use of traditional and sometimes primitive methods in developing countries to the use in industrialized countries of technologically more evolved and complex computer aided equipment. While these methods are vastly different both can produce excellent oil. The true difference comes from the operator’s skill and experience. Generally, the process of steam distillation is the most widely accepted method for the production of essential oils on a large scale.”9
Dry Distillation, has been permitted under ISO Standard 9235, which states that products of dry distillation without added water or stream are in fact essential oils. This method involves the heating without aerial oxygen in a closed vessel thus preventing combustion. The plant material used in this process is broken down into new chemical substances. Birch Tar and Cade oil are made this way but as both oils contain carcinogenic phenols they are no longer commercially demanded. Today dry distillation is only used in very rare cases.

Solvent extract with organic solvents are questioned as to whether they are true Essential Oils. “A hydrocarbon solvent is added to the plant material to help dissolve the essential oil. When the solution is filtered and concentrated by distillation, a substance containing resin (resinoid), or a combination of wax and essential oil (known as concrete) remains. From the concentrate, pure alcohol is used to extract the oil. When the alcohol evaporates, the oil is left behind. This is not considered the best method for extraction as the solvents can leave a small amount of residue behind which could cause allergies and effect the immune system.”10

“Hypercritical carbon dioxide extraction” appears to be an improvement. Unlike the products produced by regular solvents (absolutes and concretes) the solvent (CO2) can be easily and totally removed, just by releasing the pressure in the extraction chamber. This process happens in “a closed chamber where the most volatile and most fragile fractions of the fragrance and plant can be collected.”11

  2. Susanne Poth, Tea tree oil for health and well being, (Sterling, June 1999), 10.
  3. Heather S. Oliff, Ph.D. The Case for Non-Standardized Herbal Products
    Brinker, F. Variations in effective botanical products. The case for diversity of forms for herbal preparations as supported by scientific studies HerbalGram. #46, 1999:36-50.
  6. Poth. Tea tree oil for health and well being, 10.
  8. Poth.Tea tree oil for health and well being. 12.