Aromatherapy Module 2 Methods of Extraction Manual compiled by Dr Gaynor du Perez METHODS OF EXTRACTION Copyright © 2016 All Rights Reserved No part of this book may be reproduced or distributed in any form or by any means without the written permission of the author. 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 A r o m a t h e r a p y M o d u l e 2 - M e t h o d s o f E x t r a c t i o n Page 2 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 A r o m a t h e r a p y M o d u l e 2 - M e t h o d s o f E x t r a c t i o n Page 3 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. A r o m a t h e r a p y M o d u l e 2 - M e t h o d s o f E x t r a c t i o n Page 4 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.