- Steam distillation - produces a good quality oil
- Water distillation
- Carbon dioxide gas extraction - produces a higher quality oil than steam distillation (the total method is slightly better than the select method for getting more essence out)
- Cold pressed citrus oils - produces a good quality citrus essential oil
- Solvent extraction - produces a less pure oil because some residues from the solvent stay behind
All the information below this line is purely optional - extras for the super keen mixtress - the process names above are enough for you to go shopping for good quality essential oils.
Steam distillation is represented in the diagram. It is the most common method used to produce essential oils. Steam from boiling water is used to extract the essential oil from plant material. The steam rises and passes through a cold coil thereby turning into liquid. Essential oils float on top of the water in the second vessel; these are skimmed off and properly separated from the water.
The remaining water is also useful because it can be sold as a "floral water" - floral waters possess many of the qualities of an essential oil and can be used instead of actual water in my DIY Hair Care Recipes.
2. Water distillation
Hot water is used instead of steam. Some plants e.g. lavender do not take well to this method if the are left exposed to the hot water for too long much of the goodness in the essential oil is destroyed. Water distillation can be done under lower pressure to preserve more of the plant's essence and goodness.
Flower blossoms and finely powdered plant material can be extracted well with water distillation.
Both essential oils and floral waters a.k.a. hydrosols are produced using this method.
Carbon dioxide gas extraction uses carbon dioxide gas, high pressure, low temperature and expensive equipment to extract essential oils. There are two types:
a. Select carbon dioxide gas extraction
In the select method essential oil is extracted at a temperature of 31 degrees celsius (88F).
- Plant material is placed in a chamber then compressed CO2 is released into the chamber;
- As the gas passes through the plant material components are extracted;
- Pressure is then lowered and the extracted plant material is separated out;
- The CO2 is completely removed from the extracted material without leaving any behind in the essential oil;
- The same CO2 is recycled to run the process again.
b. Total carbon dioxide gas extraction
In the total method a higher temperature is used. The essential oil produced contains more essence from the plant is thus a little better than the select method.
This is only done for citrus fruits.
- Fruits are placed onto a conveyer belt and dropped into a container with knives;
- The knives pierce the fruit as the container is closer releasing the juice from the fruit;
- Water is sprayed onto the peel and the pile of mush is the put into a centrifugal container to extract the essential oil.
5. Maceration extraction
With maceration, flowers (e.g. rose, jasmine) are soaked in hot oil so that their cell membranes are ruptured and the essence absorbed into the hot oil. The oil is then separated out and the essential oil bottled. This is similar to the solvent method but hot oil is used instead of a solvent.
With the solvent extraction method plant material is soaked in a solvent e.g. petroleum ether, methanol, ethanol or hexane. The cell membranes of the plant material are ruptured and the essence absorbed into the chemical.
The solvent is then separated and the essential oil bottled. However, some chemical residues are left from the solvent so the resulting oil is not pure.
The amount of solvent left could range from 6-20% with some solvents. With hexane, however, the residue left is said to be 10ppm which is a very low concentration; it's equivalent to 0.001%.
Personally, if I could prove that the solvent used was hexane and the price of the essential oil was comparatively low just for this reason then I would be happy to take my chances on this one because I spend a small fortune on ingredients for my DIY Hair Care Recipes.