Absolutely, Critically, Essentially, Expressly and Aromatic: The Distilled Truth of Essential Oil Distillation
- delilahproctor
- Nov 15
- 10 min read
Welcome back to Harvester’s Corner! During our recent article on Vanilla, I grew curious as to how many methods were used to distill these fantastic oils which we enjoy. So, since it was about time for our next science blog, I decided to take a look at the distillation methods being used.
The essential oil industry is booming. In 2021 the global market was $8.74 billion dollars US, with a growth rate of 9.5%. This means that the anticipated market value in 2028 is expected to be $18 billion dollars US. (1) This means a lot of distillation will be going on. But what is distillation, and how is it performed? From a chemistry perspective, distillation is a process used to separate the components of a liquid by using the different boiling points of the respective components. The process commonly requires a medium, termed a solvent, which combines with the components of interest to carry them away from the source matter.
What is a Solvent?
One concept we need to be clear on is this solvent. Solvents can be used to break something down. Dish-washing soap is a solvent used to clean dishes. Acetone is a solvent used to remove acrylic nail polish from fingernails and prepare the nails for a new color. It can also be used to thin industrial paints and clean equipment after painting has been performed. Mechanics often use gasoline as a solvent to clean oil and grease from automobile parts, so the parts can be better examined for defects. But where essential oils are concerned, water is the primary solvent being used. It is readily available all over the world, and its behavioral characteristics as it is heated are well-documented and well known. So when you hear the term “solvent,” take a look at the process and what kind of solvent is being used.
Ironically, the preceding concept is what peaked my attention where the Vanilla article was concerned. For those who have yet to read that article, Vanilla seed pods are distilled using super-critical Carbon Dioxide (sCO2), not water. As I researched the sCO2 process I became very intrigued at the versatility and adaptability that distillation method offers. We will talk about that in a few moments.
Historical vs. Modern Essential Oil Distillation
But first, let’s acknowledge one basic fact. Oils, specifically essential oils, as we know them today, are vastly different to what the people living in Roman times would have termed “oils.” Plant material available in the mighty Roman Forum would have been used in three primary methods. The first would have seen the plant ground up and taken internally, either as a herb or spice in food, or mixed by an apothecary into a concoction taken under a physician’s guidance. The second method would have been aromatic, with the plant ground up and combined with flammable material for use as incense in either a home, a temple, or a funeral procession. The third method would have seen the plant material used in a topical manner, with the plant mixed with either olive oil or a fatty substance like beef tallow and applied as a cosmetic to the skin. When mixed with the tallow, the resulting cream was known as an unguent, which became the precursor of the many cold creams and ointments available today.
Combining the plant material with olive oil was a simple process and is one that is still in use in the modern day. How many people take rosemary stems and put in a bottle of olive oil and let it sit for a couple of weeks before using the oil to cook with? In Roman times, leaves were crushed, branches and twigs broken, and bark was shredded and then placed in a vat of olive oil for a period ranging from a couple of days up to a week. The oil was then filtered through a cloth, bottled, and sold in the marketplace.
What makes the oils of today different is the process, one which commonly uses steam. Steam distillation dates back to the Bronze Age, so titled by man heating and forming bronze metal into all manner of tools. Clay vessels with metal rims and caps were filled with water and placed over a fire. The steam collected on the inside of the cap and settled into the rim before it trickled down a funnel into a waiting receptacle. Surviving examples have been found in Mesopotamia (modern-day Iraq) dating back to around 3500 B.C., and Slovakia dating back to 1500 B.C. (2) Steam distillation seemed to be a very minor means of preparing oils through most of the Roman Republic and Empire. In fact, steam distillation seemed unimportant until the 8th Century, when various Arab scientists started examining ways to create new perfumes.
Steam Distillation
While several Arab scholars wrote about steam distillation, the figure most credited as being the father of the modern-day distillation process was a physician known as either Ibn Sina or Avicenna. Ibn Sina was born around 980, and at the height of his career he was known as the “Prince of Physicians.” He is credited with writing 450 books over a broad variety of subjects, with over 200 surviving to the modern-day. As part of his experiments, Ibn Sina added rose petals to water, creating the first recorded instance of steam distilled Rose Oil and its byproduct, Rose Hydrosol. (3)
The main processes we’ve talked about, namely using an organic solvent like in Roman times and steam distillation, are still used in the modern day and are two of the three conventional methods used to obtain oil. When most people think of steam distillation the image that often comes to mind is that of large stainless steel vats surrounded by tubing and pressure gauges and, in all fairness, if you were to visit a large-scale distillation center, this is likely what you would see. The reality in developing countries is very different, however. For example, Petitgrain growers in Paraguay use stills made from wooden slats held together with bailing wire. Once the still is filled with plant material, the growers make a paste of thick mud which they use to cover any cracks and seal the lid to the still. Their stills utilize steam piped in from another container. The steam filters through the plant material and then carries the oil-laden steam through a pipe attached to the lid, to a water trough, which cools the steam and separates the oil. The oil is then allowed to then drip into the collecting receptacle. Steam distillation can produce a large quantity of oil in a relatively short time span although some oils, such as Guaiacwood, require a longer time in the stills. Guaiacwood, which like Petitgrain is sourced in Paraguay, spends a minimum of seventeen hours in the still! One drawback of steam distillation is the high environmental impact from the process, namely the resources needed to heat the water to generate the steam. Many operators, especially in developing countries, try to utilize the plant material left over from the previous batches as fuel for the fires.
Cold Pressing
The third conventional method used today is cold pressing, which is frequently employed with citrus oils. These present a challenge where extraction is concerned, as the heat from the steam causes the more volatile components to evaporate. So to obtain these volatile components, the rinds are physically compressed by mechanical means. The compression releases the oil which is collected and, in some instances, further processed by a centrifuge to separate it from any non-desirable fluids released during the process. Two hallmarks of cold pressed oils are the strong aroma associated with the oil and a high nutritional value. (4) If you see a cold-pressed oil that states that it is for aromatic use only, and not to be taken internally, avoid that oil, as it has been adulterated in one form or another.
More Distillation Processes?
Advances in technology have seen newer, innovative distillation processes that have been developed over the past few decades. These new methods are more environmentally friendly and could have great potential for changing the way we source oils. We spoke of one such method in our recent article on Vanilla. This process is Supercritical Carbon Dioxide (sCO2). Carbon Dioxide is a naturally occurring gas. Humans and other animals exhale it, and plants use it to survive. The key to the process is pressurizing the gas to a point where it shows liquid-like properties. This is reached by compressing the CO2 to 1,070 psi and storing it between 87 and 88 degrees Fahrenheit (30 – 31 Centigrade). (5) Using Vanilla as an example, the dried seed pods are chopped up and placed in the still. The pressurized gas is introduced and surrounds the material. The oil is collected and piped to another chamber, where the pressure drops and the CO2 changes back to a gas and leaves the oil behind. The gas is then recycled to its supercritical state and readied for the next batch. SCO2 distillation is superior to steam as it is non-toxic, non-flammable, and utilizes low-to-moderate temperatures and pressures. Two drawbacks with Supercritical Carbon Dioxide Extraction include the fact that the system is complex and that it requires a new infrastructure in the distillation plant. (6)
Ongoing research has identified two more innovative distillation methods which show promise. These are Microwave-Assisted Extracted and Ultrasound-Assisted Extraction. The Microwave-Assisted Extraction method is unique as it can be used with a solvent, as well as without a solvent. Consider your home microwave for a moment. You put what you want to cook into the unit, set a time, and pull out the finished product at the end. This is very similar to the Microwave Distillation method. The plant material is placed in a chamber where microwave energy waves are used to separate the oil and convert it to steam. The steam is collected and cooled, where it is reconstituted as oil. Researchers have found that some plants work better with water, while other plants produce oil without water being added. A study undertaken in 2013 which looked at microwave distillation for Rose oil (Rosa damascene) indicated that the quantity of oil produced in fifteen minutes was nearly double the quantity produced by traditional steam distillation after a three-and-a-half hour run. A drawback discovered on the analysis of the oil was that the microwave-distilled oil showed a decrease of the monoterpenes (as compared with the steam-distilled oil), which lessened the market quality of the oil. (7)
Ultrasound-Assisted Extraction requires a solvent. The base concept is very similar to an ultrasonic jewelry cleaner. Once an item is placed in the chamber with the solvent, high-frequency sound waves are emitted. The sound waves create alternating regions of high and low pressure. When a high-intensity sound source is used, the alternating pressure waves can lead to the formation of tiny bubbles, which then burst. This process is known as cavitation. In the jewelry cleansing scenario, these bubbles bursting dislodge the dirt from the jewelry. In the distillation scenario, these same bubbles release the oil from the plant material. The oil is then put through a centrifuge to separate it from the solvent. Like the Microwave-Assisted Extraction, studies have revealed higher oil yields when compared with traditional distillation methods. A recent study, published in 2024, however, included a statement relating to the ultrasound extraction, and I feel that this applies to other alternative methods as well. The authors observed, “Although ultrasound proves highly effective in a laboratory scale, to transition to industrial applications presents significant scaling-up challenges.” (8) One of the challenges would be the increased power consumption required for both Microwave and Ultrasound Extraction. This is a challenge already being looked at where Artificial Intelligence Data Centers are concerned. Where will the power come from, and how sustainable a source of energy is it? Another challenge is maintaining the purity of the oil produced. What benefit is there in producing twice as much oil if the final product is not up to established quality standards? Yet another challenge, applicable primarily to the ultrasound method, is identifying the optimum frequency for the respective plant material. Some plants release better at 50 kiloHertz (kHz), while others require a higher frequency approaching 200 kHz. For comparison, the upper limit of human hearing is 20 kHz, and most medical ultrasound applications range from 3 megaHertz (mHz) up to 18mHz. A Hertz is a cycle per second, so 100 cycles per second equals 100 Hertz.
Summery
As you can tell, there is a lot of work behind the scenes where the production of the oils is concerned. There is a large overhead for the multitude of distilleries around the world where their equipment is involved. It becomes clearer with each article I write just how important the need for an organization such as Co-Impact Sourcing is. Whether it is providing a hand to beginning farmers, teaching the next generation the importance of crop rotation, paying a fair price consistently, or helping upgrade a distillery to be more efficient, Co-Impact sourcing is working diligently to help bridge the future for oil producers.
Join us next time when we look at a product I’ve come to know and love in recent years: Fennel. Until then, stay safe and keep sharing the oils!
Sources
1. Rout, Tamby, et al. “Recent trends in the Application of Essential Oils: The Next Generation of Food Preservation and Food Packaging.” Trends in Food Science and Technology, v. 129, 2022. Online. <https://doi.org/10.1016/j.tifs.2022.10.012.> Accessed 24 July 2025.
2. Schlosser, Štefan. “Distillation—From Bronze Age till Today.” Proceedings of the International Conference of Slovak Society of Chemical Engineering, 2021. Online <https://www.academia.edu/46560203/Distillation_from_Bronze_Age_till_today>. Accessed 3 July 2025.
3. Most steam distillation processes create a byproduct called hydrosol, which is a mixture of water and oil frequently used in cosmetic applications.
4. Brah, Obuah, and Adokoh. “Innovations and Modifications of Current Extraction Methods and Technologies of Citrus Essential Oils: A Review.” Discover Applied Sciences. 27 August 2024. Online. <https://doi.org/10.1007/s42452-024-06100-z>. Accessed 27 June 2025.
5. Sousa, Parente, Marques, Forte, Tavares. “Microenapsulation of Essential Oils: A Review.” Polymers (Basel). 2022 April 23;14(9) 1730. Doi: 10.3390/polym14091730. PMID: 35566899; PMCID: PMC9099681. Online. <https://pubmed.ncbi.nlm.nih.gov/35566899/>. Accessed 27 June 2025
6. AZO Materials. “Insights from Industry: The Advantages of Supercritical CO2.” Online. <https://www.azom.com/article.aspx?ArticleID=20458#:~:text=The%20 disadvantage%20of%20this%20solvent,in%20general%2C%20are%20not%20desirable.> Accessed 24 July 2025.
7. Mohamadi, Shamspur, and Mostafavi. “Comparison of Microwave-Assisted Distillation and Conventional Distillation in the Essential Oil Extraction of Flowers Rosa damascene Mill.” 7 Jan 2013. Journal of Essential Oil Research, February 2013. Online. DOI 10.1080/10412905.2012.751555. <https://www.researchgate.net/publication/271929967_Comparison_of_microwave-assisted_distillation_and_conventional_hydrodistillation_in_the_essential_oil_extraction_of_flowers_Rosa_damascena_Mill>. Accessed 24 July 2025.
8. Khalid, Chaudhary, Amon et al. “Recent Advances in the Implementation of Ultrasound Technology for the Extraction of Essential Oils from Terrestrial Plant Materials: A Comprehensive Review.” Ultrasonic Chemistry, July 2024, vol. 107. Online. <www.sciencedirect.com/science/article/pii/51350417724001627.> Accessed 24 July 2025.
Disclaimer
All views on Harvesters’ Corner are those of the author. I am a Wellness Advocate with dōTERRA, and I use the essential oils daily. Any purchases made through my affiliate link may earn me a commission. The oils are not intended to treat or cure any illness.
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