Extraction Methods for Essential Oils

Production of Volatile Oils

Extracting the essential oils from plants requires different methods, specific to the plant containing the oils. The most common method is either distillation or pressing, but other methods include injecting carbon dioxide, maceration, or enfleurage. Distillation methods include steam, water, or water and steam distillation. Solvent extraction commonly relies on alcohol as the solvent.

The method chosen relies on a few factors. If the plant has low oil content, pressing will not suffice to obtain all of the oil content. Parts of the plant, like flower petals, generally lend themselves better to distillation or solvent methods, or even maceration followed by distillation or solvent extraction. Some seeds or fruit have high oil content and can be cold-pressed, in order to generate the purest oils. Roots often are macerated to break up the fiber, then the oils are extracted by other methods.

Interestingly, although volatile oils evaporate quickly in the air, they often remain in the plant parts even after drying, since they may be trapped in the plant more effectively than water. Coriander, for instance, usually is dried after harvest, but the oils are released, sometimes months later, when pressed. This is true for most oilseeds used for food, like canola, soybean, sunflower, or corn.

Steam Distillation

Extraction of essential oils often occurs using distillation and, in particular, steam distillation. This method eliminates the need for further distillation of alcohol from volatile oils and creates a safer product, less likely to be abused.

An example of the risk of alcohol distillation misuse is the production of commercial vanilla. Many vanilla products contain 35-50% alcohol, making it a target for illicit drinking. However, many herbal remedies use a process related to alcohol distillation: tinctures. These will be discussed later.

Steam distillation requires pure, distilled water. In the process of distillation, the water steam vaporizes the plant’s volatile compounds, then the vapor is condensed and collected.

The extract produced is concentrated.

To produce a stem distillation extraction, you will require several components. The basis of the process is the “still.” Similar to that seen in the TV show, Moonshiners, but on a much smaller scale.

A still consists of a tank in which you place water, heated to create steam.  In a normal still, the main tank would contain “mash” consisting of the fermented material, along with some water. The mix would be heated to 68-70C (the boiling point of alcohol), with the vapor travelling along cooling tubes to a condenser tank. Here, the resulting condensate would consist of alcohol produced in the fermented mash and a little of the water that had evaporated.

An extraction for essential oils works a little differently.

Steam is injected into the small tank holding crushed or fractured plant material, loosely gathered. This tank is raised above the cooling or condensation lines.

The steam picks up the volatile oils, and then travels along the tubes that are looped or slightly inclined, so that they carry the vapor to the condensation tank, where the oil and water gather. The essential oils, being lighter than water and non-soluble, rise to the top and are gathered. Some, though, are heavier than water and fall to the bottom of the collector.

Some systems use a cold-water loop system in the condensation tank to cool the oil/water mixture, but this is a more complex, costlier method than a simple still.

A cautionary note: many states and provinces have strict regulations on the use of stills, in order to avoid the making of ethyl alcohol, or home brew, by private entities. Check your local regulations prior to making your still.

Solvent Extraction

This method has more risk associated with it than steam distillation, because it uses food-grade solvents that include hexane and ethanol. Hexane is considered highly carcinogenic, and is banned in any quantity in the air during the oil refining process, yet the FDA allows it to be used as a solvent for foods, so long as it leaves only miniscule amounts behind.

Hexane is used to produce soy margarines, canola oil and margarines and other oilseed products.

However, oils, waxes and pigments in the plant material are more easily dissolved in alcohol and hexane, since they do not dissolve in water.

Some aromatics and delicate plant material are unable to withstand the pressure of steam distillation. Others may yield low amounts of oil. Solvents draw out almost all of the resins and oils from these plants. With solvent extraction (particularly alcohol), a finer fragrance than by any other extraction method also results.

Once the solvent has been introduced into the plant material, a waxy compound, called “concrete,” is generated and mixed with alcohol. This releases the oil particles. The solvents, however, remain in the oil and the compounds are used in the aromatherapy, cosmetic or perfume product. Aromatherapy oils, therefore, should never be used internally, and any topical use should be done with caution.

CO2 Extraction

This process is not a method that can be undertaken at home. It requires expensive and specialized equipment.

Because the heat is controlled in CO2 extraction, the quality of the oils is often higher than for steam distillation.  In CO2 extraction, none of the constituents of the oil are damaged by heat.

The primary difference between steam and CO2 extraction is that CO2 is used as the dissolving agent, rather than heated water. CO2 operates at 95-100F (38-40C).

This process’ purity is seen in such oils as Chamomile, where steam distillation “browns” the oils, while CO2 leaves the natural green tinge to the oil. The oils also are thicker than steam-distilled oils, since there is no water remnants in the CO2 production. This gives off more of the aroma of the original herb and holds more of the original constituents in the oils than steam.

 To extract the oils, liquid (pressurized) CO2 is injected into the plant material chamber, absorbing the oils. When the CO2 returns to a gaseous state, the residue is pure oil. Since CO2 is colorless and odorless and is completely removed when pressure keeping it as a liquid is relieved, when it is off gassed, there is no environmental or health harm done.

Maceration

Maceration may seem like a complex concept, but it is nothing more than crushing or fragmenting the plant material before extracting the oils. It is the same process that is used in making a tincture, except without using alcohol.

The resulting oils are known as infused oils.

To begin the process, pound, cut or grind the dry plant material as fine as possible. It is important that the material is dry, to avoid having the oils go rancid after production. Moisture also encourages microbial growth. Use 5% Vitamin E oil to reduce the risk of rancidity.

Use a carrier oil as a solvent. Good carrier oils are olive, almond, or grapeseed oil. These also absorb into the skin more safely and efficiently than petroleum oils, making them suitable for massage oils or topical applications.

Mix the oil and plant material and store in a closed glass container. Allow the mix to stand for a week or two, shaking occasionally to mix. Then, strain the solid residue out. Press the oily solids to retrieve more of the oil. Lastly, clarify the liquids using filtration. Cheesecloth works well for this purpose.

Pour the end product into an airtight container and store in a cool, dark place for up to twelve months.

Enfleurage

This is a fancy name for one of the oldest methods of volatile oil extraction. Using either animal fat or vegetable fat, oils are drawn from the delicate flowers, buds, and petals, by pressing the plant parts into the fat. Over days, weeks or even months, the essence of the flowers is infused into the fat. Ideally, the fats are odorless and solid at room temperature. This makes coconut oil particularly useful.

As the petals fatigue, or lose their color and scent to the fats, they are removed and new ones pressed into the fat. Using a hot fat speeds and intensifies the process. This method is used for the same flower parts, but also is better for heavier petals and other more dense oil-carrying plant parts.

The last steps are to wash the fats with alcohol, which removes the oils. Sometimes, the oil/alcohol is used directly as a scent (perfume or aromatherapy) and sometimes the alcohol is allowed to evaporate. The fat left behind is used to make fragrant soaps.

Cold Press Extraction

This process is similar to pressing olive oil and is employed with citrus peels and other oily or moisture-laden parts. The press separates the oils and water from the plant parts. Next, the liquids, containing suspended solids, are centrifuged to separate solids from liquids. The oils separate from the juice, generally with the oil rising to the top and being skimmed off.

Water and Steam Distillation

This process uses the same equipment as an alcohol still, and the macerated plant parts, with water, are distilled using the same process, except that steam is introduced externally to the mash mix.

Water Distillation

Delicate plant parts, like blossoms and flowers, are inserted in boiling water to separate the oils. Once the liquids cool, you can separate the small amount of oils that separates, as well as use the water as a fragrant water (rose water, etc.).