Essential Oils. Part 2
F rom time beyond all memory, people have been searching for ways to get the "soul of plants": essential oils. That is the unique elixir, which can replace almost all the contents of our first-aid kit. Natural antibiotics, antiviral, antifungal and immunomodulating agents, which have no side effects and are not addictive are not a myth. Today we will try to tell you about both traditional and modern technologies that allow us using the full power of essential oils, the real 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 water, and hydro distillation, 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 least loss of useful compounds in its composition. It is believed that only two methods allow to derive 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”, which is 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 aromatic and water vapor enters the condenser through the steam hose. It passes along a long spiral tube through a special "refrigerator", and its temperature gradually decreases. This makes the vapor cool back into liquid form.
Next step, this liquid substance gets into so-called Florence, or separating, flask, which is basically a receptacle with two drain tubes. Water and oil do not mix. If the specific gravity of the essential oil is less than the specific gravity of water, it floats as a layer on top of the water, and water will be drained off through a tube located at the bottom of the separator. Otherwise, if the oil is heavier than water (e.g., such as clove essential oil), it is found at the bottom of the separating flask, and water will be 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.
Not all aromatic plants can be treated with hot steam. The essential condition is a high oil content in the parent plant, along with its resistance to 100 ° C temperatures, and a 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. In the novel by Patrick Süskind "Perfume" (and in the eponymous movie), this method is well illustrated. It is based on the natural absorption of volatile substances by non-volatile 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 sorbent is completely absorbed by the essential oils. Withered petals are replaced with fresh ones, repeating the procedure until the fatty base is completely saturated with oils. This semi-finished product is called floral pomade, if animal fat was used as a sorbent. In 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 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 the hand, it becomes fluid. It is important to understand that absolute is not pure essential oil, but its mixture. In fact, this is solution, with other components of the plant, mainly with vegetable fats.
A modern type of enfleurage is the method of 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. Remember the nice smell on your hands after you peel a grapefruit or a mandarin. This invigorating light aroma is given to a fruit by natural oil, the content of which in citrus can reach up to two percent of the weight of the fruit. The simplest technology that was practiced in ancient times is a hand pressing. A little later special spiked drums were invented, where fruits were rolled on the surface, puncturing the skin and collecting 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, then add a little water and press; on the output there will be a mixture of water, juice and essential oil. 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 for aromatherapy or cosmetics, it is better not to use such oils. Fruit for juice is grown using a lot of chemical fertilizers, the fruit rind is sprayed with special compounds for long-term storage, and many hazardous chemicals can penetrate into the essential oil. Therefore, you should choose the essential oils made by specialized companies, who do not save on the processes of cultivation, harvesting and production.
Many aromatic plants can not be distilled because of the low content of essential oil (e.g. rose, jasmine, narcissus), or because of the instability of the oil components to high temperatures. In this case, solvent extraction is used; a very popular method, first tested in the 1930s. Just a few volatile organic solvents are suitable for this process; they have to have some certain characteristics, such as: high degree of purification, low boiling point, and no odor. The solvent, reacting with essential oils, should not originate substances that may contain toxins or can alter the smell of the product. 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 special 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 completely 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 substances 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 concrete. Accomplish this, the concrete is dissolved in ethyl alcohol, and filtered from insoluble wax particles and unnecessary impurities. The solution is discolored with activated charcoal and evaporated in vacuum. As a result, we get the already known absolute and resinoids (fragrant resin extracts, which are used in perfumery to give the composition durability). However, some traces of the solvent can remain in the 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 to derive an oil of extremely high quality, without foreign inclusion, exposure to high temperatures or pressure. At temperature of 33 ° C and pressure of 200 atmospheres, the carbon dioxide is in an aggregate state in between gas and liquid. This empowers it with dissolving properties, which makes it possible to extract essential oils almost instantaneously; and without further solvent removal. Most often, 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.