How are essential oils extracted?

During peak fresh lavender season, Nature's Pure Essentials used some of Sunshine Lavender Farm's crop for a Triangle Aromatherapy Meet-Up. 

We had such a good time and Caryn mentioned that sunshine lavender farm's lavender was one of the loveliest lavenders she has distilled.

Sue Dwiggins

Owner, Nature's Pure Essentials

Caryn, owner of Essential 3 Essential Oil Company,
showing the stove top distiller.

So, how are essential oils extracted? Let's start with a little history ... 

1. History of Distillation

The Practice of Distillation

Distillation appears to have been practiced throughout ancient times. Based upon the current interpretation Paolo Rovesti’s discovery of an earthenware distillation apparatus, the production or extraction of aromatic oils by means of steam distillation has been known for 5000 years. During the fifth century AD, the famed writer, Zosimus of Panopolis, refers to the distilling of a divine water and panacea. Throughout the early Middle Ages and beyond, a crude form of distillation was known and was used primarily to prepare floral waters or distilled aromatic waters. These appear to have been used in perfumery, as digestive tonics, in cooking, and for trading.

Although an extensive trade of odoriferous material has been shown to have occurred in the ancient Orient and ancient Greece and Rome, the oils used were not essential oils per se, “rather they were obtained by placing flowers, roots, and other plant material into a fatty oil submitting the glass bottles containing these mixtures to the warming influence of the sun and finally separating odoriferous oil from the solid constituents”.

In 900 AD, Avicenna, the famous child prodigy from Arabia who wrote many documents on plants and their uses and also instructions for massage, was accredited with refining the process of distillation by improving the cooling system.

Today distillation is still the most common process of extracting essential oils from plants. The advantage of distillation is that the volatile components can be distilled at temperatures lower than the boiling points of their individual constituents and are easily separated from the condensed water.

Fresh lavender is harvested at its peak in mid June in North Carolina.
The lavandula x intermedia was selected for its high oil content.

2. Methods of Distillation

Water/ Steam Distillation

a. Water distillation: The plant material is placed in boiling water. The steam and oils are captured and then separated out to produce the essential oil.

b. Steam distillation: The straight steam method involves pushing steam through the plant material and then picking up the essential oil.

c. Hydro diffusion: The steam comes thru the top rather than the bottom, there is a shorter distillation time and it is used mainly when extracting essential oils from woody or tough material or seeds.

Solvent Extraction: Some plant material is too fragile to be distilled and an alternative method must be employed. Solvent extraction is the use of solvents, such as petroleum ether, methanol, ethanol, or hexane, to extract the odoriferous lipophilic material from the plant. The solvent will also pull out the chlorophyll and other plant tissue, resulting in a highly colored or thick/viscous extract. The first product made via solvent extraction is known as a concrete. A concrete is the concentrated extract that contains the waxes and/or fats as well as the odoriferous material from the plant. The concrete is then mixed with alcohol, which serves to extract the aromatic principle of the material. The final product is known as an absolute. After the solvent extraction process has been completed, the resulting absolute will have an extremely low concentration of solvent residue, approximately 5 to 10ppm (parts per million). The current European Union standards are for less than 10 parts per million solvent residues in a finished absolute.7 However, even with such a potentially small residue (less than .0001%), many aromatherapists disagree with the use of absolutes for individuals with a compromised immune system due to the potential effect of the residual pesticide.

However, absolutes do have therapeutic value and are often used for psychological purposes and for animals, particularly horses. Many therapists incorporate absolutes,

such as rose absolute, jasmine, and tuberose, as a valuable part of their therapeutic applications of aromatherapy. Ultimately the decision to use absolutes is up to the practitioner and his/her own personal preferences. Absolutes are highly concentrated aromatic substances and are obtained from delicate flowers by either enfleurage or solvent extraction. Absolutes will most often resemble the natural aroma of the plant and are normally more colored and viscous than essential oils. Absolutes are used extensively in the cosmetic and perfume industries due to their strong aromas. There are also different grades of absolutes. The top grade is the uncut, which can be a thick or semisolid substance, making them difficult to work with. Less expensive grades are diluted with alcohol to make them more user friendly, although often the strength of aroma is slightly diminished.***Solvent extraction is used for jasmine, tuberose, carnation, gardenia, jonquil, violet leaf, narcissus, mimosa, and other delicate flowers. Neroli and rose can be distilled or solvent-extracted. The name neroli typically implies the essential oil, whereas the name orange blossom is commonly used for the absolute or hydrosol of neroli. The name rose is used to describe either the essential oil or the absolute. Companies selling essential oils should clarify whether the product you are purchasing is an essential oil or absolute. This information should be on the label and in the product catalog

Expression: Also referred to as cold pressing, is a method of extraction specific to citrus essential oils, such as tangerine, lemon, bergamot, sweet orange, and lime. In older times, expression was done in the form of sponge pressing, which was literally accomplished by hand. The zest or rind of the citrus would first be soaked in warm water to make the rind more receptive to the pressing process. A sponge would then be used to press the rind, thus breaking the essential oil cavities, and absorb the essential oil. Once the sponge was filled with the extraction, it would then be pressed over a collecting container, and there it would stand to allow for the separation of the essential oil and water/juice. The essential oil would finally be siphoned off. A more modern method of extraction, and less labor-intensive, has been termed the ecuelle a piquer process that involves a prodding, pricking, sticking action to release the essential oil. During this process, the rind of the fruit is placed in a container having spikes that will puncture the peel while the device is rotated. The puncturing of the rind will release the essential oil that is then collected in a small area below the container. The end process is the same as above. The majority of modern expression techniques are accomplished by using machines using centrifugal force. The spinning in a centrifuge separates the majority of essential oil from the fruit juice.

Enfleurage is a cold-fat extraction process that is based upon the principles that fat possesses a high power of absorption, particularly animal fat. The fat used must be relatively stable against rancidity. It is a method used for flowers that continue developing and giving off their aroma even after harvesting (e.g., jasmine and tuberose). Today, Grasse continues to be one of the few areas in the world that continues to employ enfleurage as a method of extraction, although it is rare in the aromatherapy market due to the expense. If one finds a jasmine enfleurage on the market, this would typically be considered an absolute.

Hypercritical carbon dioxide (CO2) extraction is a relatively new process used for the extraction of aromatic products. The basic concept is that CO2 under pressure will turn from a gas into a liquid that can then be used as an inert liquid solvent. This liquid solvent is able to diffuse throughout the plant material thus extracting its aromatic constituents. CO2 extracts contain most of the same constituents as their essential oil counterparts, although they can contain some elements not found in essential oils. For instance, the essential oil of ginger (Zingiber officinale) does not contain the bitter principles, however the CO2 extract does. Also, the CO2 extract of frankincense (Boswellia carterii) has immune enhancing and anti-inflammatory activity not found in the essential oil. CO2 extracts are known for their strong similarity in aroma to the actual plant aroma. ***The three main disadvantages for this process are cost, potential pesticide residue, and the lack of information regarding their safety and therapeutic benefits. With regard to pesticide residue, Guba comments that “carbon dioxide extraction has been demonstrated to concentrate from 7 to 53 times more pesticide residues in the final extract.” Therefore, it seems pertinent to only use organic plant material for CO2 extraction. Perhaps as more CO2 extracts become available and more practitioners use them, further details regarding their applications will become apparent.

3. Parts necessary for the Steam/Water Distillation Process

• Heat source

• The holding tank which holds both the water and, just above the water will sit a grid or false bottom; i.e. similar to a vegetable steamer

• Botanical material to be distilled

• The condenser, which collects the steam and cools it, usually by piping it through a tube immersed in cold water

• The separator, which separates the essential oil from the water vapor. The separator is one of the most important pieces of apparatus a distiller can have. This enables the distiller to separate the essential oils from the distillate in a passive manner.

4. Process

• The botanical material is placed upon a grid inside the still. Once inside, the still is sealed and depending upon the method, i.e. water/steam will slowly break through the plant material to remove its volatile constituents. These volatile constituents rise upward through a connecting pipe that leads them into a condenser. The condenser cools the rising vapor back into liquid form. The liquid is then collected in a vehicle below the condenser. Since water and essential oil do not mix, the essential oil will be found on the surface of the water where it is siphoned off. Occasionally an essential oil is heavier than water and is found on the bottom rather than the top, such as with clove essential oil. The temperature of the steam needs to be carefully controlled, enough to force the plant material to let go of the essential oil, yet not too hot as to burn the plant material.

• The steam which now contains the essential oil molecules passes through a cooling system to condense the steam, which forms a liquid from which the essential oil and water is then separated.

• The steam is produced at greater pressure than the atmosphere and therefore boils at above 100 degrees Celsius which facilitates the removal of the essential oil from the plant material at a faster rate and in so doing prevents damage to the oil.

***Some oils, like Lavender is heat sensitive (thermolabile) and with this extraction method, the oil is not damaged and ingredients like linalyl acetate will not decompose to linalool and acetic acid.

5. Can Distilling Equipment Affect the Oil? YES!

The size and material of the cooking chamber, the condenser type and the separator may all affect the outcome of the oil.

The cooking chambers that are best are made of non-reactive metal. This minimizes the essential oil from being adulterated (changed) by reactive metals such as copper and aluminum. The best metal that is non-reactive is stainless steel!

6. What other Factors Effect Distilling Essential Oils?

They are other factors such as temperature and pressure that affect the quality of oil. If the pressure or temperature is too high than the chemical constituents of the oil when overheated may change, the pH and polarity may also be altered.

7. Essential oil Yield examples

• Cypress Essential Oil – If we start with 2,000 pounds of material we produce 1 pound of oil. The pressure in pounds must be 0 and the optimal distillation time and temperature is 220 degrees at 24 hours! Anything less, produces oil that has 18 to 20 constituents missing from the oil completely!

• Tea Tree Essential Oil (Melaleuca alternifolia) – If we start with 1,000 pounds of material we produce ten to fifteen pounds of oil. The pressure in pounds must be 3 and the optimal distillation time and temperature is 218 degrees for 2-3 hours.

a. Define extra (Ylang Ylang) and 5 & 10 fold

FOLDER: is an essential oil that has been further distilled and concentrated from its already highly concentrated form. Citrus oils (like orange, lemon, grapefruit, lime, tangerine, blood-orange, mandarin, and bergamot) are the most commonly found in "folded" versions, and the most common "folds" are 5-fold and 10-fold. The main benefits of using a folded oil are:

• They are more concentrated/stronger oilsThey are more likely to be "purer" scents - more closely resembling the fruit/plant that they were distilled from. Often they are called "sweeter" "juicier" or "bolder."

• The terpenes that are removed as part of the distillation process are more volatile and prone to oxidation. Since the terpenes have been removed, the essential oils will last longer, both in your soaps or candles and in the bottle.

• The terpenes are also what make the essential oils phototoxic (causing sensitivity to the sun). This is not a problem for soap, since it is a "rinse-off" product. But in "leave-on" applications like lotions and lip balms, you don't want to use phototoxic essential oils. Since the terpenes are removed as part of the process, folded citrus oils are o.k. for use in "leave-on" applications like lotions and lip-balms. (Because each distiller and manufacturer may have different processes for distillation, be sure to verify this with your essential oil vendor, though.)

EXTRA: Ylang Ylang essential oil is generally sold in a number of grades – extra, first, second and third. Extra is the most expensive and chemically can be judged by its ester content. This, however, can be easily manipulated.

Basically the grades are arrived at by fractionating the distillation process. The "extra" is derived from the oil being taken at a given time, say two hours after the start; No's 1, 2 and 3 following suit.

8. What is a hydrosol / By-product of Distillation

Also, known hydrolats, are the by-product or product (depending on the distiller purpose) of the distillation process. Hydrosols contain the water-soluble constituents of the aromatic plant and retain a small amount of essential oil. Every liter of hydrosol contains between 0.05 and 0.2 milliliter of dissolved essential oil, depending on the water solubility of the plant’s components and the distillation parameters.

Note: The addition of essential oils to water is not at all the same as true hydrosols, and it is recommended that you read the ingredients label on products to ascertain whether or not you are getting a true hydrosol. When water and essential oils are mixed together with or without a dispersant, this is called a “spritzer” or “aromatic spritzer,” and this product should not be confused with a true hydrosol.

9. Chemistry

Essential oils are a mixture of fragrant organic compounds common to a number of plants. Commonly composed of two primary groups: 1. hydrocarbons 2. Oxygenated compounds. The chemical constituency determines the properties specific to each oil.

The above information was provided during the Triangle Area Aromatherapy Meet-Up on June 14, 2014. 

Thank you Sue, Caryn and all of the lavender loving friends who participated!