Building Protocols for Essential Oil Distillation


Or should I say, the process of learning what NOT to do. In similar fashion to everything else in grad school, building methods and protocols for my research has been challenging. One of the biggest components of my project is to extract and evaluate the essential oils of the 14 different varieties of holy basil. I went through 2 months of information gathering and trial and error just to figure out the proper procedure to distill and collect an accurate mass of essential oil.

I wrote about it here, but the first challenge was figuring out what glassware to get for the distillation. All the literature I read used a ‘modified clevenger trap’. I searched all the glassware companies,  I looked on eBay, I consulted with my food science committee member. Finally I found the right glassware from Wilmad-LabGlass.


It is called a clevenger trap for oils lighter than water and allows the essential oil layer to collect over a layer of water. The arm that connects the two vertical pieces takes extra condensed water back into the flask so the distillation can run continuously without having to add extra water during the distillation.

Once I found the glassware I had to get the rest of the items needed to set up a distillation, this included a round bottom flask and a condenser.


The flask sits in a heating mantle connected to a rheostat (keeps temperature constant). The flask contains ground up holy basil and water. The flask is connected to the clevenger trap and a condenser sits on top of that. The condenser has two parts. The inner part that is exposed to the vapor and the outer part that has cold water running through it. When the water boils it releases vapor that is mixed with the vaporized essential oil and travels up from the flask. As it hits the condenser on top, the water and essential oil condense and form two layers in the clevenger trap.

I looked up the ratio of water to holy basil in the literature.  For each distillation I am using 50 grams of ground holy basil to 650 mL of water. So, I obtained extra holy basil for testing, I measured everything out and started the distillation. Then I realized my first mistake.


My flask was too small and it boiled up into the clevenger trap.


I also started taking notes and making a list of everything I needed just to prepare for the distillation, a bowl and scale for measuring out 50 grams (usual lab scales only go up to ~30 grams), coffee grinder to grind up the plant material, funnel to get the powdered herb into the flask, strainer to strain plant material from the water after distillation, vials to store the extracted essential oil, labels for the vials, etc…


I collected the supplies I needed. Then I got a bigger flask and added glass beads to the ground up holy basil and water to keep things boiling evenly.


I ran the distillation again and everything worked out great. You can see the vapor coming up the clevenger and condensing to create a layer of essential oil, and extra water traveling through the connecting arm back into the flask.


The next problem was the question of how long to run the distillation. I went back to the literature and couldn’t get a clear answer. Some papers said 90 minutes, some went as long as 6 hours. I began to ask around. I called a lab in North Carolina that does essential oil composition analysis, I called 6 or 7 essential oil companies and distilling companies and nobody knew. Since I was dealing with a small glass distillation set-up they couldn’t give me any advice, since normal essential oil companies work in much larger quantities and they use stainless steel or other metals for their distillation apparatuses. The labs I called usually  just do a composition analysis by extracting the essential oil with a solvent like hexane. This tells them what compounds are in the essential oil, but not how much total essential oil is in the plant. We want to know how much essential oil each plant produces, so we have to extract it through distillation.

After much deliberation, we finally decided to just run the distillation until 30 minutes after we collected our last amount of oil. This took 3 hours. With set-up and cleanup each distillation takes 3.5 hours. 3.5 hours is a long time and I have 84 samples to run before April. But at least we were making progress. We finally figured out our set-up and how long to run the distillation to collect the essential oil.


The next challenge was to figure out how to get an accurate mass of the essential oil collected. Like I said earlier, knowing how much essential oil is produced in the plant is an important piece of quantitative data, especially since our goal is to make a recommendation to growers on which variety of holy basil to grow. You will find out tomorrow how we did that!

To read more about my research, funding, and masters program, check out my page, Holy Basil Research.

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