There are many ways to extract oils from plant material, some of which result in inferior oil, or oil that has a significantly reduced shelf life. For example, soaking lavender in alcohol will produce a nice scent... but the result is weak and the oil may fade within months. Other methods are costly, or even impossible for the average person to attempt - this includes most methods to extract oils from delicate flowers, like roses.
The method I will describe provides a fair amount of essential oil, with a moderately long shelf life (a year or more). This is a simplified distillation process that works best with oil-heavy herbs like lavender or sage. It is not appropriate for extracting the delicate oils from any flower. Henceforth I shall describe the process as it is used for lavender.
First, the list of materials. You will need a stove, a large pot for the distillation - most probably one you would use for soups or the like. The size of the pot you have available will determine the rate at which you can extract oil, so find the largest that will reasonably fit on your stove. You will also need a metal bowl that fits snugly into the rim of the pot, a large supply of ice, a smaller pan that fits easily inside of the pot, and a mechanism to keep the smaller interior pan above water level. Some suggest a brick for this, though anything that is clean, flat, and does not float is appropriate. You will also need a dark, glass bottle to put the oil in when the distillation process is complete. If you so choose, you may wish to strain the oil from the water - for which you would need a separating funnel or a fine cheesecloth.
You will need large amounts of lavender, and the type of lavender you use will affect the quality of the resultant oil. That is, if you wish to sell lavender oil commercially, neither this distillation method nor your common garden variety lavender will be helpful! A general ratio of lavender-to-oil is approximately 0.25 to 0.5 ounces of oil per pound of lavender.
Now, do the following:
- Set up the pot on the stove, with the smaller pan inside of the pot, held up by a flat, non floating object.
- Confirm that you have an extensive supply of ice.
- Collect copious amounts of lavender from your garden. Collecting the herb gently can help preserve oils. Avoid crushing flowers, leaves, or stems if at all possible.
- Put a layer of lavender on the bottom of the pot, up to the base of the interior pan. Fill the pot with water to the base of the interior pan. Make sure the pan is not floating - if it shifts position you may lose some of the oil you are trying to collect!
- Place the metal bowl onto the pot, making sure it fits snugly. Fill this bowl with ice.
- Simmer the water in the pot for several hours - from one to four hours, depending on the size of the pot - periodically replacing ice in the metal bowl and scooping out melted water.
- When the process is complete, remove the metal bowl from the pot and take the interior pan from inside the pot. If the process has worked correctly, the pan should be full of a mixture of water and oil.
- If you so choose, you may strain the oil from the water, using a cheesecloth or a separating funnel.
- Repeat the process until you have the desired amount of essential oil, or until you run out of plant material.
How does this process work? This is similar to steam distillation, in which plant material is suspended above boiling water, the steam is condensed in tubing, and water collects in an adjoining apparatus. In this case, the steam condenses on the bottom of the metal bowl and drips into the interior pan. This steam is a mixture of the oil of the plant in the pot and water.
Cheap chemistry sets may include distillation apparati, which can simplify the process - and provide a greater amount of oil per pound of plant matter. However, the size of these sets may limit the rate at which you can extract oil, and are often breakable and more complex to use in the distillation process.
If you keep the oil you have extracted in a dark place, stoppered with a wooden cork (rubber corks can affect oils), it should last for more than a year, and be fragrant enough for homemade perfume, soaps, shampoos, or for baths (when used properly, and only certain herbs).