The story (feel free to skip down to The Question):
Last night, the BF's mom asked me about EOs versus FOs (as the incredibly patient BF sighed in the background and clicked through Gizmodo). I gave her the basic rundown--synthetic v. natural, etc. But then she asked, "Are there coffee EOs?"
"I don't think so," I said. "You'd have to use an FO."
"Why not?" she asked.
And... I had no idea.
The question: Why not? Coffee beans are oily. Why are some things EOs but not others? Why lavender but not gardenia?
I have a cabinet of these things but don't know how they're made or what makes certain ingredients (tulips, honeysuckle) unsuitable or impossible to make into EOs.
Enlightenment much appreciated!
EOs are produced by steam distillation which has already been mentioned. Some plants don't produce enough EO to make distilling viable, and others are ruined by heat.
Absolutes are different from EOs in that they contain more of the non water soluble parts of the plant making them more *complete*, and they are produced using solvents. A lot of Aromatherapists won't use absolutes as they believe some of the solvent will be left in the resulting *oil* making it less therapeutic. They are used extensively in high end perfumery though. This method is often used with plants which don't yield good results from steam distillation such as jasmine and some rose. They are often extremely costly though as it take a lot of plant material to produce.
Some plants will not yield a good *oil* with either of these methods such as violet, and are being tested using different methods so maybe in the future...
A more recent method called CO2 extraction may provide better results and also something called "headspace" (I think?) extraction.
I have had relatively good results using an oil maceration with flowers such as violet and use the resulting fragrant oil as a base in some of my oil based perfumes and solids.