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Various methods of extraction of Essential oils


Essential oils are extracted from the plant material in various ways, depending on the part of the plant that is used for extracting the oils. Essential oils are extracted from the flowers, seeds, leaves, stems, bark, trunk and roots of various plants. There are three basic ways for extracting essential oils.

Cold Pressing

One of the oldest ways of extracting essential oils is by crushing the plant material. Parts of the plant that have high oil content such as seeds, fruit peels, fruits, are crushed to express the oil from the plant material. The material is then filtered to separate the oil from the rest of the plant material. Some common examples are cold pressed lemon oil, Neem oil, and various seed oils. The quality of the oil, depending on the material, is very good because the plant material is not altered in any significant way.

Steam Distillation

For parts of the plants that do not have a high oil content or where it is difficult to crush the plant material, steam is used to extract the essential oils from the plant. Essential oils from roots, leaves, woods are generally extracted using steam distillation. Some flowers such as Rose, Lavender, Ylang Ylang, are also extracted by steam distillation. In the steam distillation process, steam is first generated in a boiler. The steam is sent through the bottom of another vessel wherein the plant material is kept. As the steam rises through the plant material, it softens and releases the essential oils that are present in "sacs" in the plant material. The essential oil rises along with the steam and is sent through a tube that is kept cool with running water. As the steam and essential oil cool, they condense into a liquid mixture of oil and water. The oils and water are then collected and separated. Because of the difference in density of the oil and water, the oil floats above the water or sinks to the bottom. The steam that has cooled into water, has some of the essential oil remaining in it. These waters then form what are called floral waters, such as rose water from the distillation of rose oil.

Common examples of steam distilled essential oils are: Rose oil (flower), Sandalwood oil (wood), vetiver oil (root), Patchouli (Leaves), Lemongrass (grass), etc.
Solvent Extraction

Parts of the plant that are delicate and that can be damaged by the high temperature of the steam are extracted by using solvents at cooler temperatures. Usually flowers such as Jasmine, Tuberose, Champaka are extracted by solvent extraction. Flowers such as rose are extracted by both the steam distillation process as well as by solvent extraction. Essential oils extracted using solvents are generally referred to as absolutes.


The solvent that is used, has to be of a low boiling point, so that it can be separated from the plant material with minimal heating. The most common solvent used is hexane. The solvent is passed through the plant material where it absorbs, the essential oils, waxes and fatty material from the plant. The solvent is then removed from the plant material under low pressure. The lower pressure helps to boil off the solvent at a lower temperature. Once the solvent is removed, the resulting mixture of essential oils, and fatty material is called a concrete.


The next steps involve separating the essential oil from the fatty material. The concrete is 'washed' with alcohol. The alcohol absorbs the essential oil leaving the fatty material behind. The mixture of alcohol and essential oils is then heated at low temperature under vacuum to separate the alcohol from the essential oil. The essential oil left behind is now called the absolute.


One of the newer techniques to separate essential oils from the plant material at low temperatures is by using liquid carbon dioxide or by using supercritical carbon dioxide. Carbon dioxide, a gas at normal room temperature and pressure, is pressurized to form a liquid or depending on the temperature and pressure a supercritical fluid. A supercritical fluid behaves both as a liquid and as a gas. Supercritical carbon dioxide has a higher extractive capability compared to liquid carbon dioxide, and therefore is the fluid of choice when extracting from plant material that have low yields of essential oils.


Liquid carbon dioxide, which is easier to produce, is used in the extraction of material that have a higher percentage of essential oils, for example, spices.


The liquid or supercritical carbon dioxide is produced and passed through a tank where the plant material is kept. The carbon dioxide extracts the essential from the plant material and then sent into a separation vessel. The separation vessel is kept at a temperature and pressure where the carbon dioxide would normally exists as a gas. In the separation vessel, the liquid or supercritical carbon dioxide turns into gas, and releases the essential oil. The essential oil 'condenses' in the separation vessel and is removed.


Essential oils produced by supercritical or liquid carbon dioxide have an excellent quality. Because the process involves very high pressures and sophisticated controls, the essential oils produced by this process are much more expensive.


Factor affecting quality of extracted essential oils

The quality of the essential oils produced by any of the above methods can vary greatly depending again on various factors. Two of the main factors are:

1. The quality of the starting plant material.

As is obvious, it is very critical to start with a good quality material. For example, vetiver root has to be about 5 years in the ground for it to produce a good quality oil. But for economic reasons, some of the roots are extracted after two years, thereby affecting the quality of the oil produced. The quality will also depend on keeping proper separation of the plant material needed for extraction. For example, if the essential oil is to be extracted from the leaves, care has to be taken to separate the stems, and twigs from the leaves before distillation.


Soil conditions and environment affect the quality of the oil produced. Sometimes different geographical regions produce different grades of oils. Plants grown during different seasons produce difference grades oils.

2. Process control during extraction of the essential oil.

During steam distillation, different grades of oil are produced or different fractions are produced. The first fraction is usually of the best quality whereas the oil coming out from an 'exhausted' material is usually of lower grade depending on when the first extract leaves the distillation still. Maintaining proper separation between the various grades is important for the final quality of the oil.


In some distillation units where the plant material and water are heated together, the plant material may get damaged by overheating or localized charring.


During solvent extraction, if the temperature and pressure are not controlled properly, some of the solvent may remain behind in the absolute causing a foul odor.