People have been searching for ways to get the "soul of plants": essential oils from time beyond all memory. That is the unique elixir, which can replace almost all the contents of our first-aid kit. Natural antibiotics, antiviral, antifungal, and immunomodulating agents with no side effects and are not addictive are not myths. Today, we will try to tell you about traditional and modern technologies that allow us to use the full power of essential oils, the natural healers of the plant world.
Steam distillation (Lat. distillatio – "dripping") is one of the oldest methods, which have been used at least since the 5th century AD. There are two main methods of distillation: direct, in which plant raw materials are dipped directly into the water, and hydrodistillation, where plants are laid on a grid through which hot steam passes. Hydro distillation is the most popular and cost-effective option, as it allows you to get a large amount of essential oil with the minor loss of valuable compounds in its composition. It is believed that only two methods allow deriving pure essential oil; these include steam distillation and cold pressing. Let's take a closer look at this process. Pre-cleaned and cut-up plants are placed into a large container called "still", usually made of stainless steel. Then hot steam, injected through the plant material, breaking down the cells, which contain essential oil, releasing the plant's aromatic molecules, and turning them into vapor. The mixture of fragrant and water smoke enters the condenser through the steam hose. It passes along a long spiral tube through a particular "refrigerator", and its temperature gradually decreases. It makes the cool vapor back into liquid form.
Next step, this liquid substance gets into the so-called Florence or separating flask, which is a receptacle with two drain tubes. Water and oil do not mix. Suppose the specific gravity of the essential oil is less than the specific gravity of water. In that case, oil floats on top, and water drains off through a tube in the bottom of the separator. Otherwise, if the oil is heavier than water (e.g., clove essential oil), it is found at the bottom of the separating flask and water removed through the hole in the upper part of the flask.
Essential oils derived by steam distillation: sandalwood, tea tree, ginger, lemongrass, cedar, patchouli, etc.
Can treat not all aromatic plants with hot steam. The essential condition is the high oil content in the parent plant, its resistance to 100°C temperatures, and the small size of molecules; such oils are most easily evaporated. Some essential oils, such as chamomile or yarrow oil, can only be derived by distillation. However, for oils extracted from a particularly delicate and tender raw material, such as jasmine petals, orange, and rose flowers, other technologies are used: enfleurage, maceration, solvent extraction, dynamic adsorption, and extraction with carbon dioxide.
Enfleurage is another traditional way of obtaining essential oils, which has survived from the remote past to our days. This process is quite long, time-consuming, and, as a consequence, expensive, so from the middle of the twentieth century, enfleurage is used quite rarely, mainly for elite varieties of essential oils. This method is well illustrated in the novel by Patrick Süskind "Perfume" (and in the eponymous movie). It is based on the natural absorption of volatile substances by nonvolatile solvents, such as animal or vegetable fats. The technology looks like this: glass or fabric base, mounted into a frame, is coated with a layer of fat, so-called sorbent. Then, the petals of flowers or whole inflorescences are manually laid on fat and left until the essential oils absorb the sorbent entirely. Withered petals are replaced with fresh ones, repeating the procedure until the fatty base is wholly saturated with oils. This semi-finished product is called floral pomade if animal fat was used as a sorbent. In the case of using vegetable fats, that would be fragrant oil. Then this substance is placed in alcohol until completely dissolved, and then the alcohol is evaporated or distilled off in a vacuum. The resulting compound with a high content of essential oils is called “absolute” and usually has a viscous consistency. However, the absolute of rose oil at room temperature is solid, and only when the bottle is warmed up in hand becomes fluid. It is essential to understand that final is not pure essential oil but its mixture. It is the solution, with other components of the plant, mainly with vegetable fats.
A modern type of enfleurage is dynamic adsorption, where activated carbon serves as a sorbent. A stream of hot moist air is passed through the raw material placed on the mesh in a sealed chamber. Then the air, saturated with oil vapors, is absorbed by activated carbon; the coal is placed in ethyl ether, and after distilling the solvent off, there is pure essential oil.
Maceration (Lat. “macerare”) differs from enfleurage in the fact that the raw material is preliminarily cut up and placed in a receptacle filled with a vegetable oil or animal fat, pre-heated to 50-70°C. The mixture is infused for a certain amount of time with a periodic replacement of the plant material; after that, it is filtered.
For each ether-bearing plant, there is the most optimal way of obtaining oil. For citruses like grapefruit, orange, lemon, mandarin, bergamot, and many others, the best method is cold-press extraction. The great virtue of cold pressing is that the temperature caused by the pressure at the moment of pressing does not exceed 40° C. Thus, there is no heating and subsequent destruction of nutrients and trace elements. Most of the essential oils are concentrated in the zest, in microscopic "tanks" right under the surface of the fruit. Do you remember the pleasant smell on your hands after you peel a grapefruit or a mandarin? This refreshing light aroma is given to the fruit by natural oil, the content of which in citrus can reach up to two percent of the weight of the fruit. The most straightforward technology practiced in ancient times is pressing by hand. Unique spiked drums were invented a little later, where fruits were rolled on the surface, puncturing the skin and collect the juice. Nowadays, of course, industrial extractors are in use, but the essence of the technique remains the same. Cut off an upper layer of zest, add a little water, and press; there will be a mixture of water, juice, and essential oil on the output. Set the mixture aside and wait until the oil rises to the surface, or separate it with a centrifuge. In our industrial age, many factories, which produce packaged citrus juice, use the remaining cake to make essential oil by pressing, distillation, or solvent extraction. The economic benefits are obvious, but it is better not to use oils for aromatherapy or cosmetics. Fruit is grown using many chemical fertilizers. The fruit rind is sprayed with unique compounds for long-term storage, and many hazardous chemicals can penetrate the essential oil. Therefore, you should choose the essential oils made by specialized companies, which do not save on cultivation, harvesting, and production processes.
Many aromatic plants can not be distilled because of the low content of essential oil (e.g., rose, jasmine, narcissus) or the instability of the oil components to high temperatures. In this case, solvent extraction is a prevalent method, first tested in the 1930s. Just a few volatile organic solvents are suitable for this process; they have specific characteristics: high purification, low boiling point, and no odor. The solvent, reacting with essential oils, should not originate substances containing toxins or alter the product's smell. These requirements are met by petroleum ether, hexane, pentane, diethyl ether. In simplified form, the extraction process can be described as follows: a fine-cut vegetable material is placed into a particular device called the Soxhlet extractor. In the bottom flask, the solvent is heated until it starts evaporating; the vapor is rising upward and entering the cooling chamber where it condenses; the solvent drips through the plants and enters the lowest flask again. After that, the cycle is repeated until the solvent is wholly saturated with essential oil. Then, the volatile solvent is removed by an inert gas stream under reduced pressure. At the end of this stage, a solid or semi-solid waxy compound is formed. It contains 5 to 20% of essential oil and consists of volatile aromatic and nonvolatile components (waxes, resins, paraffin, esters of higher fatty acids). But wait, there is more.
The next step is the extraction of essential oil from the waxy compound. Accomplish this, and the waxy compound is dissolved in ethyl alcohol and filtered from insoluble wax particles and unnecessary impurities. The solution is discolored with activated charcoal and evaporated in a vacuum. As a result, we get the already known absolute and resinoids (fragrant resin extracts used in perfumery to give the composition durability). However, some traces of the solvent can remain in oils derived in this way, so they are not recommended for internal use.
Essential oils derived by solvent extraction: rose, tuberose, jasmine, neroli, violet, lavender, orange blossom.
Since the 1980s, carbon dioxide has been used to extract essential oils. This method, called CO2-extraction, allows deriving an extremely high-quality oil without foreign inclusion, exposure to high temperatures, or pressure. At a temperature of 33°C and pressure of 200 atmospheres, the carbon dioxide is in an aggregate state in between gas and liquid. It empowers it with dissolving properties, making it possible to extract essential oils almost instantaneously; and without further solvent removal. Such plants as cloves, hops, lavender, chamomile, ginger are processed this way. Unfortunately, the disadvantage of this method is its high cost. Therefore, essential oils derived by СО2-extraction are used mainly in up-scale perfume, cosmetics, or medicines.