Are essential oils essential?

By Clive Larkman

2021 and it seems we are living in a crazy world. Without looking at COVID-19 and its maddening repercussions, we need only to look at the ever-evolving world of medicine, herbs and therapies to really be confused.

On the positive side, there is a greater acceptance of non-traditional Western therapies, however, an understanding is far from simple. Modern medicine takes influence from a wide range of indigenous cultures and many historic health beliefs. Most are based on concoctions of herbs and animal products. Some, mostly European, utilise essential oils.

So, the initial question is, what is an essential oil? At first glance, one would assume that it is something essential for survival and/ or good health, sort of like an essential vitamin or essential amino acid – but you would be incorrect. Etymology is the study of where words come from and how they evolve.  It can be fascinating following the evolution of language. The word ‘essential’, in essential oils, comes not from a perceived need, but from the origin of the oil and how it relates to the plant from which it comes.

In the case of ‘essential oils,’ the term is derived from the word essence. This refers to the fact that the extracted oil comes from the components of the parent plant that give it the flavour or aroma and which we call its ‘essence’, in the same way as we might say the ‘essence’ of Thai food is the ginger, coriander, garlic and chilli used in the cooking. We can say that the ‘essence’ of what makes lavender so appealing, is the oil that is extracted from the flowers.

Essential oils are extracted from plants and should reflect the natural smell and flavour of those plants’ concentrated plant extracts that retain the natural smell and flavour, or ‘essence’, of their source. They should be extracted using one of a few base methods and must be pure and unadulterated to be truly called an essential oil.

Traditionally, they were used in health therapy but are now a major part of our food and beauty industries. The gross worldwide production is in excess of 250,000 tons per annum. The major oils used worldwide are lemon, lavender, mint, cedar, peppermint, bergamot, orange, eucalyptus, clove and Tea tree. The largest by far is citrus (lemon, orange and bergamot), which is used in multiple food products, the biggest being Coke/Pepsi. The quantities are huge, especially in the food and beverage industry, where they are used as antioxidants, preservatives and flavours.

As mentioned above, essential oils are extracted from plants and reflect the essence of the plant. The oils come from all parts of the plant, depending on the species. Lavender oil comes from the florets, whereas sandalwood oil comes from sandalwood timber. The percentage yields vary from as low as 0.01% to 5%, with wholesale prices commensurate with yields.

The main form of extraction is distillation, where the concept is to purify the oils by removing unwanted products based on the relative volatilities. Steam distillation is predominantly done for most plants. Regular steam is generated by some form of boiler and is passed through a mass of the relevant plant matter. In doing so, the steam fractures the oil sacs and picks up the oil. It then moves up through the distillation vessel and is collected and passed through a condenser. As it moves down the condenser, the steam turns to water and when it settles in the separation unit the oil sits on top of the water. Once the distillation process is completed, the oil and water are separated. The oil is put in a dark vessel and stored at cool temperatures until needed. Sometimes the air above the oil is replaced with liquid nitrogen. 

The remaining water is called hydrosol. This has the same fragrance as the essential oil as there are minuscule particles of the oil still in suspension. The hydrosol makes great room fresheners and has lots of uses as a dilute spray. It does carry some of the benefits of the oil but nowhere near the potency. Some people attribute a whole range of medicinal benefits to hydrosol. These are doubtful at best.

The majority of essential oils are produced using this method in stills of varying size and shape. The vessel holding the plant material may be as small as 2L or as large as 5000L. There have been thousands of articles written on the design and shape of the vessels, with some authorities believing the ratio of height to diameter is critical in getting the best distillation results. The reality is a good distillation unit basically needs a constant source of steam, taller than wide in shape and a good operator.

The other main methods are solvent extraction, absolute extraction and cold pressing. Solvent extraction involves using two chemicals to dissolve and then separate the constituents, using their relative solubilities as the driver. Absolute extraction uses a hydrocarbon solvent to produce a ‘concrete’ and is the blend of the solvent and the oil, which is then treated with alcohol to extract the concrete. The resultant product is cooled and then the alcohol is evaporated off to produce the ‘absolute’. Cold pressing involves pressing the raw plant to ‘squeeze out’ the relevant oils. The system now uses a centrifuge to extract the oil and is predominantly used for citrus oils because they can be damaged by the high temperatures involved in steam distillation.

Next month we will look at some of the major oils in the world, their composition and how they are used. Although we see so little of the oils in our life, they form a small but important part of our medicinal, food and beauty products.