Aromatherapy

Module 2

Methods of Extraction

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Essential oils are derived from the flowers (e.g. chamomile), leaves (e.g. tea-tree), seeds (e.g. black pepper), fruit rind (e.g. lemon), heartwood (e.g. sandalwood), bark/sap/resin (e.g. frankincense) and rhizomes/roots (e.g. ginger) of aromatic plants. The word “oil” is misleading, as essential oils are not oily, but are volatile essences which, if exposed to air, will evaporate quickly.

Unfortunately, extracting essential oils is not an easy process . Invariably the method of extraction either affects the chemical make-up of the oil, adds other components or both.

The overriding objective is to cause the least amount of aggression and interference, resulting in oils as close as possible to their natural composition.

Historically, distillation was the only method that produced what was termed essential oil. However, whilst it does facilitate the collection of the favourable tiny, volatile, aromatic molecules from the plant, distillation is far from perfect. The aggressive use of heat alters the chemical composition of the oil and some oil is lost through evaporation.

Some methods of extraction produce aromatic substances which, although highly perfumed and possessing some therapeutic properties, are not actually classified as essential oils. This does tend to get a little confusing, particularly as many refer to all aromatic products as essential oils.

For example, absolutes, extracted using solvents, are highly fragrant and highly concentrated. However, as they contain the heavy aromatic molecules, waxes, colour pigments, fatty acids, vitamins and minerals, as well as the tiny, volatile molecules that would be derived during the distillation process, they are not technically essential oils.

The arrival of new methods of extraction such as hydro-diffusion and phytol-extraction (which are producing quality oils) has added to the grey area surrounding the definition of an essential oil.

There is no simple rule that we can give as current opinion is so widely spread. What you must ensure is that you are aware of the various methods of extraction and the effects of each on the quality of the oil produced. Also bear in mind that, in many cases, oils can be extracted from a plant using more than one method. For example, frankincense can be distilled to produce ‘essential oil’ or subjected to solvent extraction to produce an absolute.

Let’s look at the various methods used to extract essential oils and other useful aromatic substances from plants. The main points are listed first, followed by more detailed information.

Distillation

The plant material is heated from below with hot water or steam causing the tiny, volatile, aromatic molecules to vaporise. This vapour is then condensed and the essential oil separated from the water.

Hydro-Diffusion (Percolation)

Steam is passed down through the plant material causing the vaporisation of the tiny, volatile, aromatic molecules. The process is then similar to distillation in that the vapour is condensed and the essential oil separated from the water. Although this method is not

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widely used commercially, it has been found to be more efficient for the extraction of wood or tough plant material, such as seeds.

Expression

The essences are squeezed out of the rind of citrus fruit.

Solvent Extraction

Solvents, such as hydrocarbons and alcohols, are used to absorb aromatic molecules from plants. The solvent is then evaporated, leaving behind the essential oil. The end products are not classed as essential oils but rather fall into the following categories:

Resinoids

These solid or semi-solid substances (e.g. benzoin) are produced from the resins or gum like substances from the bark of trees.

Concretes

These solid, wax-like substances (e.g. rose otto) are produced from leaves, flowers or roots.

Absolutes

Absolutes (e.g. jasmine) are highly concentrated, highly fragrant, thickish, coloured liquids which can be prepared from a concrete using alcohol.

Enfleurage

Flowers are spread over cold vegetable fat, allowing the aromatic molecules to be absorbed. When the fat is saturated with the oil, it is washed in alcohol. The alcohol is then evaporated, leaving the absolute. This method is used to extract oils from delicate flowers such as Rose, Jasmine and Tuberose. It is labour intensive and a very slow process, and for this reason the cost of Rose and Jasmine absolute is very high in comparison with average essential oils. This process can take up to three months.

Maceration

Flowers are plunged into hot vegetable oil (60 to 70 degrees) and kept warm for a few days, allowing the aromatic molecules to be absorbed. The resulting liquid is then filtered, leaving the perfumed oil.

Infusion

With infusion, the plant material is placed into a container of carrier oil. It is kept warm for 2 to 3 weeks and when the plant material discolours, it is removed and replaced. This is done repeatedly until the oil is infused with the aroma of the plant. Together with the perfume, the oil absorbs many of the plant’s therapeutic properties. This infusion is known as floral oil if flower petals have been used to make it, or herbal oil if made from any other part of the plant.

Carbon Dioxide Extraction

Absolutes are extracted from the plant using carbon dioxide at high pressure and at a very

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low temperature.

Phytol-Extraction

This very new method avoids the use of heat, solvents or gas to extract the natural oils.

Now that you have read the main points, let’s look at each of the extraction methods in more detail, starting with distillation.

1. Distillation

Distillation is the oldest, most widely used method of extracting essential oils from plants and is also considered to be the most economical. Remember that it is not without its faults, as the aggressive use of heat alters the chemical composition of the oil and some oil is lost through evaporation.

The timing of the distillation process after harvest varies from plant to plant, and so the skill of the distiller is critical to achieve the optimum amount of essential oil.

Below is a diagram representing the distillation process:

The process of distillation can be broken down into 6 steps:

1. The plant material is heated from the bottom with either hot water or steam.

2. The heat causes the tiny, volatile molecules that make up an essential oil to evaporate.

3. These tiny molecules are taken in the steam along a pipe into the condenser.

4. In the condenser, the pipe containing the oil molecules and the steam pass es through cold water.

5. The reduction in temperature causes the vapour to condense back into liquid form.

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6. As the density of the essential oil differs from that of the water, the oil either floats (if it is lighter) or sinks (if it is heavier). This allows the essential oil to be easily separated from the water.

The process of distillation creates aromatic waters as a byproduct. Aromatic waters contain some soluble components of the essential oil, together with some of the larger plant molecules which, although they do not evaporate, are also water-soluble.

Due to the presence of essential oil components, aromatic waters do have some of the properties of essential oils. However, the presence of other molecules affects the aroma.

2. Hydro-Diffusion (Percolation)

This is a very new method of extraction and the process is both simple and quick. Steam is passed down through a container holding the plant material. The vapour produced is then treated in the same way as in distillation: condensed and then separated.

Hydro-diffusion is generally quicker than distillation. As the plant materials are subjected to the steam for a shorter period of time, the essential oils produced tend to be of a better quality and have an aroma closer to that of the plant.

3. Expression

Expression is the process by which the essences are ‘squeezed out’. It is used only for the oils of the citrus family (e.g. lemon, orange, bergamot, grapefruit, mandarin and tangerine) where the oil is located in little sacs just under the surface of the rind.

Until approximately 1930 the ‘sponge’ method was used. The fruit rind was squeezed by hand using a sponge. When the sponge was saturated the oil was then squeezed out of it. This process was labour intensive and it is now done by machine.

As expression does not use steam, the best citrus oils are extracted using this method. Expressed oils contain both tiny molecules (as collected in distillation) and large molecules such as waxes.

4. Solvent Extraction

Solvent extraction is a process in which solvents are used to absorb aromatic molecules from plants. The end products (resinoids, concretes and absolutes) are not classed as essential oils, but are still highly therapeutic and highly perfumed products with some uses to the Aromatherapist.

Resinoids

Resins are the gum-like substances produced from the bark of trees or bushes. Solvents, usually hydrocarbons (e.g. benzene, hexane) or alcohol, can be used to extract the aromatic molecules from resin. The solvents are then removed by distillation, leaving the highly perfumed, solid or semi-solid resinoids.

Concretes

Concretes are solid, wax-like substances that can be extracted from plant materials such as leaves, flowers and roots using hydrocarbons (e.g. benzene, hexane) as the solvent. The solvent is then removed by distillation. Concretes are often used in food flavouring.

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Absolutes

Absolutes are prepared from concretes by using alcohol to extract the aromatic molecules . The alcohol is then evaporated leaving the thickish, coloured liquid known as the absolute. They are also produced by enfleurage and carbon dioxide extraction.

Absolutes are widely used in the world of perfumery and also have uses in Aromatherapy. Due to the method of extraction absolutes, as the name suggests, are absolutely complete in their aromatic complement. They contain not only the tiny, volatile, aromatic molecules (as collected during distillation) but also the heavy molecules, waxes, colour pigments, fatty acids, vitamins and minerals. Absolutes can also retain traces of the solvent used in the extraction process, which may be irritating to the skin.

There is a school of thought that questions the use of absolutes in Aromatherapy, due to the lack of therapeutic value of some of the components and the presence of the solvent. However, it has been shown that absolutes do not always contain traces of solvents and the appreciation of absolutes is growing.

It is important to remember that absolutes are highly concentrated. They must therefore be used in lower concentrations than the essential oil.

5. Enfleurage

Enfleurage is a process in which specially prepared cold vegetable fat is used to absorb the aromatic molecules from plants.

A thin layer of the cold vegetable fat is spread onto a sheet of glass, mounted in a rectangular frame. A layer of freshly picked flowers is then spread over the fat. In approximately 24 hours, all the aromatic molecules are absorbed. The flowers are then carefully peeled off and another layer of flowers applied.

This process is repeated for many days until the fat is saturated. At this stage the perfumed fat is called pomade. The pomade is then washed in alcohol which extracts the aromatic molecules. The alcohol is then evaporated leaving the highly concentrated, highly perfumed absolute.

Enfleurage is very labour intensive and so it is not commonly used these days.

6. Maceration

Maceration uses hot vegetable oil as a solvent. The flowers are chopped up, plunged into hot vegetable oil and kept warm for a few days. The vegetable oil penetrates the plant’s cells and absorbs the aromatic molecules. The flowers are then removed from the oil and the process repeated with fresh flowers until the oil is saturated.

The resulting liquid is then filtered, leaving the ‘macerated’ oil. This highly perfumed oil can be used in its own right or the process can be taken one step further. The macerated oil can be washed in alcohol and the alcohol evaporated to produce an absolute.

7. Carbon Dioxide Extraction

This is a relatively new method of extracting absolutes using carbon dioxide at high pressure and at a low temperature. No trace of carbon dioxide can be detected in the oil

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and so this method obviously eliminates the problem of the possible presence of solvents in absolutes.

This method requires very expensive, complicated equipment. The oils produced are very similar to those in the plant. They are pure, stable, smell exactly like the flower from which they were extracted, but are currently costly.

8. Phytol-Extraction

This is a new method developed by Dr. Peter F. Wilde. The oils produced, it is claimed, are naturally prepared from organically grown, freshly harvested herbs and flowers. The plant material is placed in a glass cylinder that is then sealed at both the top and bottom.

Then, using new technology, the droplets of oil present in the plant material are extracted without the use of heat, acids, alcohol, oxygen, toxic solvents or even water. The oils produced are therefore pure and complete with all their natural fragrant and active components.

Tiny glands in the flowers, leaves, seeds, fruit, heartwood, bark, stalks, twigs, roots and rhizomes of many plants contain essences. It is believed that these odoriferous chemicals are formed in the plant by biosynthesis (the name given to the production of chemicals by a living cell). A major part of this is photosynthesis.

Photosynthesis uses the chlorophyll (the green pigment produced by the chloroplasts in the leaves of green plants) to trap light energy. This light energy is used to split the water molecules present in the plant into hydrogen and oxygen. The oxygen is either released into the atmosphere or used in other metabolic reactions. The hydrogen combines with carbon dioxide (which is naturally absorbed by the plant) and various sugars are formed. Further cellular metabolism produces complex and variable molecular structures from these sugars. The oils produced as a result of these reactions depend upon the genetic characteristics of the plant.

Many possible reasons why plants produce these oils have been put forward. It has been suggested that they may attract or repel insects, defend against the invasion of parasites, regulate the plants’ temperature, help to heal tissue wounds, promote growth, act as an emergency food supply or they may simply be by-products!

In nature the essence is slowly released but when the plant material is crushed or heated the glands burst and the strong aroma is emitted.

The value of these essences was realised many hundreds of years ago, and today a variety of methods are used to extract them. Upon extraction, the essence is generally referred to as ‘essential oil’.

The production of essential oils is big business. Aromatherapy only accounts for the use of approximately 2% of the oils produced, much overshadowed by the perfume and food flavouring markets.

The quality of the oil required by these markets also varies. The perfume and food flavouring industries require the oils to produce the same standardised aroma or flavour time after time. Therefore, it is perfectly acceptable, and indeed sometimes necessary, for the oils used by these industries to be ‘adulterated’ or changed in some way. For example,

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they may be mixed with: another cheaper oil or alcohol; a synthetic product; or may be synthesised altogether. As well as standardising oils, adulteration also reduces the resale cost as the volume of oil is effectively ‘stretched’.

An adulterated oil may have the same aroma as a pure oil, but often it will not ‘linger’ as you would expect. Its therapeutic value may also be affected. Therefore, adulteration is not a favourable practice to the Aromatherapist, to whom the quality of the essential oil is of vital importance.

Producing large quantities of essential oil is by no means easy. It is labour intensive, costly and requires a vast amount of plant material. For example, it takes about 2,000kg of rose petals to extract 1 kg of essential oil and over 6,000kg of orange blossom to derive 1kg of neroli.

Oils are now being extracted from all over the world. For example, Grasse in the South of France is notable for its production of lavender and rose, and America produces large quantities of peppermint. As well as their widespread production, their uses are also becoming universally recognised.

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