CHEMISTRY OF PERFUMES II: THE ESSENCE OF ESSENCES

Now that we already have an overview of the process of producing perfumes, how about knowing in more detail each stage of the process? In this text, we will talk about the first stage, which is the basis for the production of the aroma, the extraction of the essential oils.

Now that we have an overview of the history of perfumes, let’s talk about the first stage of perfume production, which is the essential step of extracting the essential oils.

Extraction of vegetable oils

There are several methods that allow the extraction of vegetable oils, such as: steam distillation, boiling, solvent extraction, enfleurage, maceration and expression. Essential oils can be extracted from various parts of a plant, including flowers, leaves, stems, barks, roots and even seeds. The choice of extraction method is related to the part of the vegetable and its sensitivity as well as the sensitivity of the essential oils themselves to heat and other factors.

Steam Distillation → This is the most widely used process for extracting essential oils worldwide, as it allows the oils to be extracted from a variety of plant species and plant parts. For plants very rich in starch, the oils generated may have undesired characteristics, since the starch under high temperatures ends up undergoing a caramelization process and the oil ends up with a burnt aroma. Even so, this can be minimized by adjusting some process parameters, such as the time of exposure of the plant material to the method.

This process is also called drag distillation and is very similar to simple distillation. The vegetable material is placed in a container containing water. A source of heat vaporizes the water and the water vapor generated entrains the natural oils, which vaporize with the thermal shock. This vapor containing the oils passes through the plant material and the oil and water vaporize. This steam containing the essential oils passes through tubes cooled with water and condenses. As the product, there are the essential oils and an aqueous product called hydrolate. Both are easily separated by decanting. A scheme of this process for extraction of essential oils can be seen in Figure 2.

Figure 2: Steam distillation scheme for extraction of essential oils

Boiling → This process is similar to steam distillation, but the plant material in an enclosed container is placed in cold water and brought directly to the boil for a few minutes. The extraction usually takes place at temperatures below 100oC to avoid the loss of sensitive compounds. The boiling time depends on the plant material, since barks and roots generally require more time than stems and leaves. It is a slow and relatively obsolete process, but it is still used in some cases.

Solvent extraction → This process is used for sensitive plants that lose certain components when subjected to temperature processes, such as steam distillation or boiling. In that case, the plant material is placed in rotating tanks and a solvent, usually benzene or petroleum ethers are poured over the flowers, extracting the essential oils. The flowers dissolve in the solvent, giving rise to a waxy material that contains the oil, called concrete. This concrete is placed in ethanol, which dissolves the oil. A heat source is used to evaporate alcohol which, once fully evaporated, leaves a higher concentration of perfume in the background. A schematic of the process can be seen in Figure 3.

Figure 3. Extraction scheme of essential oils by solvent

Enfleurage → This process is used for the extraction of essential oils from more delicate raw materials such as flowers, especially pink, jasmine and violet. It is a very slow method, artisanal and high cost, but that has been revived more and more with the help of high technology. In the traditional process, the flowers are scattered on grease coated glass sheets. The glass sheets are placed between moldings of wood forming a “sandwich” as shown in Figure 4. The flowers usually remain in this mixture for a few weeks and are removed by hand and replaced by fresh petals. The process is often repeated several times until the grease has absorbed its fragrance. After that time, the fat is filtered to give an aromatic oily concentrate which is then, as in the case of solvent extraction, mixed with an alcohol which is distilled to give the essential oil.

Figure 4. Enfleurage method for the extraction of essential oils from flowers

Maceration → This process is similar to the enfleurage method but heated fats are used to absorb the odor of flowers. Then the fat is also put in alcohol to get the essential oils.

Pressing → The cold pressing method is the oldest and simplest for extraction of essential oils. It is the most used method for extraction of oils from citrus fruits. Often, this process is carried out by the juice producers themselves, who pour fruit into a hydraulic press and the juice and oils are extracted simultaneously. The oils are then removed with water in an emulsion consisting of oils, water and other solid particles. This mixture then passes through a cyclone, obtaining an oil rich phase, a water rich phase and a solids rich phase. The oil rich phase then passes through a series of centrifuges for clarification and concentration and then goes through a settling for final separation.

This method is not only used for the extraction of citrus oils, but also for certain vegetable oils such as almonds, nuts and others which, in aromatherapy, are widely used to convey or dilute the essential oils themselves.

Figure 5. Cold pressing for extraction of essential oils

This text belongs to the author and should not be reproduced without permission from BetaEQ and the same.

Author of: Clarissa Alves Biscainho

Chemical Engineer – Multinational Company – Germany

Sources: Methods of Extraction of Essential Oils; How Products Are Made; How Perfumes Are Made.