Essential oils are natural oil extracts from plants. They do have healing and therapeutic properties and have been used for centuries in medicine, cosmetics, aromatherapy and in many other fields.
How essential oils are extracted
There are several methods for extracting oils and aromatic substances from plant materials. Strictly speaking, essential oils are those extracted through distillation or expression. These two methods ensure that all the essential oil is not lost or changed in composition
This is the most widely used method and the most economical. Expertise is needed to make sure all essential oil is collected and the composition is not changed. Some plants are distilled immediately after harvesting, while others are left for days or even dried before extraction.
In this method of essential oil extraction, the plant material is heated, either by placing it directly in water and bringing it to boil or passing steam through the plant material. The heat caused the cells of the plant material to burst open and release the essential oils. The essential oil molecules and steam are carried along a pipe and channeled through a cooling tank, where they cool down and are collected in a vat. The liquid that comes out is a mixture of water and essential oil. Essential oils do not dissolve in water. This makes it easy to separate them. Essential oils that are lighter than water float on the surface and heavier oils such as clove will sink.
The cooled steam is rich in aroma and is recycled. It may be used as perfume water, such as lavender water and rose water.
During the distillation process, only the small volatile molecules are able to evaporate. Essential oils that which contain a high proportion of the smallest molecules are referred to as top notes, while those composed of the heaviest molecules are referred to as base notes. The ones with molecules in between top notes and base notes are referred to as middle notes.
Top notes oils are the most volatile. The aroma disappears within 24 hours. Examples are basil, grapefruit, lemon, lime, and eucalyptus. They tend to be stimulating and uplifting.
Middle notes oils have an aroma that lasts for 2 to 3 days. Examples are chamomile, geranium, and lavender. They are generally balancing, and primarily affect the general metabolism and the systems of the body such as digestion and menstruation.
Base note oils are the least volatile and will last at least one week. Examples are frankincense, myrrh, neroli, patchouli, and vetiver. They have relaxing and sedative qualities.
The first distillation is usually the best quality. Essential oils can re-distilled through a process known as rectification. The second and subsequent distillations will produce cheaper oils that are unsuitable for aromatherapy.
Expression (Cold pressing)
This method is reserved for members of the citrus family. These include bergamot, grapefruit, lemon, lime, mandarin, and orange. The essential oil yield is found in small sacs found under the surface of the rind.
This process was originally done by applying hand pressure, collected with a sponge and once saturated squeezed into a container. Due to the time and labour costs for the squeeze, sponge and container method, expression is done using an expression/pressing machine. Citrus for therapeutic purposes is best done using naturally grown fruit.
This process is employed to flowers, gums, and resins. It does not yield essential oils but absolutes and resinoids.
This process is employed to achieve high yields or where other methods cannot work. An example is Jasmine, which is adversely affected by heat, water, and steam.
To yield an absolute, the aromatic plant material is extracted by hydrocarbon materials such as benzene or hexane. The aromatic plant material is covered with the hydrocarbon and then slowly heated to dissolve the aromatic molecules.
Next week, we will look at how to use essential oils.