Hydrodistillation of Holy Basil Essential Oil

*This post is part of a series of posts based on my research as a masters student at UGA. To find out more go to my page Holy Basil Research.


The moment we have all been waiting for. Running a real distillation on a real sample of holy basil from my research!!

If you have been keeping up with the blog you have read my posts on building the protocols for distilling the essential oil, and collecting it for analysis. You might have also read about how my research plan has changed since I started grad school last summer. This change of plans meant I had to do a preliminary screening of the fall harvest of holy basil samples by combining the three reps of each variety into one sample.


To do this, I used equal amounts from each of the three reps for plant #3. Otherwise I would do the same thing for a normal distillation, just with 50 grams of plant material from one sample.

So, before I begin each distillation I have to get my plant samples out of the freezer, bring them to the lab and measure out 50 grams of plant material. I use a coffee grinder to powder the plant material and then use a funnel to get it into the 2 liter round bottom flask.


I measure out 650 mL of water and add it to the flask.


Finally, I add in 10 glass beads to the flask. This keeps the plant material from getting stuck or boiling up the sides of the flask.


Then I take the flask and the heating mantle over to the fume hood and connect it to the rheostat (it controls the temperature).


Then I connect the clevenger trap (read more here).


Then I put the condenser on top of that.


The last step is to connect the condenser to the water supply. The bottom opening of the condenser connects to the faucet and the top opening of the condenser flows into the drain. Then I turn on the rheostat and record the time in my notebook.


I wash all the dishes from weighing and powdering the herb.


After about 20 minutes of heating up, the water starts to boil and I begin to see steam and essential oil vapor traveling up the glassware.


When that happens I turn down the rheostat to keep things at a low simmer.


As vapor goes up the tube it hits the condenser and collects in the clevenger trap.


Each distillation takes 3 hours from turning on the rheostat. So while the distillation is happening I prepare for collecting the essential oil.


I have to build my pipette filters for filtering the essential oil after distillation. I take a glass pipette, roll up some glass wool and measure out .65 grams of anhydrous sodium sulfate.


This allows me to filter the essential oil after I collect it to remove any water residue.


Then I get the beakers ready for weighing out hexane and collecting the second fraction of essential oil by covering them with parafilm. A fancy type of saran wrap used in labs.


I record the mass of my essential oil vial and beakers. At this point I still have 2 hours to kill so I usually work on homework, blogging or other pertinent research activities :).


Once 3 hours have passed, I turn off the rheostat, turn off the water, disconnect the tubing and condenser, and take the flask over to the counter.


I let off a little water from the bottom until the top of the essential oil layer is in line with the top red line. Then I can record a volume measurement for the essential oil.


Then I position my glass pipette with the glass wool and sodium sulfate over an amber vial.


I use a pipette to extract the essential oil from the top.


And pipette it over the top of the sodium sulfate.


Once the majority of the essential oil passes through I remove the amber vial and replace it with a beaker covered in parafilm.


Then I measure out 1 mL of Hexane into another beaker covered in parafilm and record the mass.


And pipette the hexane over the sodium sulfate to wash through the second fraction of essential oil.


Then I record the mass of the collected essential oil, and the second fraction of essential oil with the hexane.


I printed off some data collection sheets and have taped them into a notebook to keep track of all the numbers for each distillation.


At the end of the distillation I have to wash all the dishes.


I also have to strain out the plant material from the water and sift through it to find the glass beads.


I pick them out, wash them off and store them for next time.


Then I hang up all the glassware to dry.


While the glassware is drying I do my calculations to determine the % oil from each sample. I have completed all 14 distillations for our preliminary screening, and I have gotten a range from 0.6%-1.35%. This tells me that there is definitely a difference in yield of essential oil between plant varieties.


At the end of the distillation and data collection, I place my vials of pure essential oil for analysis in the freezer. The next step is to figure out how to use the Gas Chromatograph Mass Spectrometer to do the analysis. I keep reminding myself, one step at a time :).

Thank you for reading! I hope you enjoyed learning about distillations and essential oils.

To find out more about my research, you can go to my page, Holy Basil Research.

One Response

  1. Which plant produced the greatest yield? Where can we ready a paper with your results. Very interesting research. I am very interested in your research. Thank you for publishing your blog!

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