Essential Oil Extraction, The Theory
At Its Simplest
Heating plant matter in water until the oils are released, and separating them.
That's it. Incredibly simple, but as with many things a simple theory doesn't always make for a simple practice. However in this case, once you have the equipment, it is very accessible.
In the rest of this article I'm going to dissect some of the details that are involved with extracting oils from your favorite herbs.
Simple, but important. Whether you are foraging or gardening, it is best to have control over how your plants are harvested. Every kind is different. Some plants provide the most oils when they are flowering, others not so much. Many have their oils concentrated into a specific part of the plant that may be more fragile. Improper handling could sacrifice much of your harvest.
This topic however is as complex as the number of plants that exist in nature. So it's best to get a field guide/encyclopedia and do your own research.
Is Drying Worth It?
For do-it-yourself approaches most agree that simply cleaning the plant and drying off excess water, is as much preparation as needed. However others who are engaged on a larger scale contend that drying the herbs for days or weeks is beneficial.
Even though you'll lose some oil to evaporation, you'll be more efficient in your processing. As one can fit many more dried plants in a boiler than fresh ones. It will also have a distinct effect on the final product, giving it less of a "green" quality.
I'd recommend trying it both ways, especially if experimenting with medicinal applications.
This part is simple. You stuff as many herbs as you can fit into the pot, fill with water, and heat it all up until it's boiling. Just be aware of a few things.
Ensure that there's enough water in the boiler to last the length of the extraction (up to 6 hours). Also do your best to get the cleanest and softest water you can. Hard water is not as effective.
Don't let it get too hot, you may damage the oils before you have a chance to collect them. Depending on how full it is, you may need to keep an eye on the boiler to make sure that the steam is moving as it should. Nothing blocking its escape and nothing leaking.
Aim for a steady temperature that is appropriate for the oil being extracted.
Again very simple. If you have a professional still you simply need to ensure everything is flowing as it should, and the condenser is kept cool. For a diy build, be careful that nothing is leaking and the joints are all properly sealed.
Last, but not least, the oil must be separated from the water that it was condensed with. This is accomplished with an oil-water gravity separator. But it doesn't need to be very technical. A tall thin container would allow you to easily separate the two and siphon the water off as you'd like.
Once everything has been separated, store the oil in an airtight, tinted glass container. Leave as little headroom as possible, any interaction with oxygen will only serve to diminish its shelf life.
Be sure to carefully clean and rinse all of your distilling equipment, and that's about it.