The yield of essential oil from each plant can be quite different, after all not all plants yield up the same amount of essential oil. Let us look at just a few examples:
Peppermint yields about 0.3 – 0.4% volatile oil
Spearmint yields about 0.7% volatile oil
Sweet Marjoram yields about 0.2 – 0.8% volatile oil
Rosemary yields about 0.5% volatile oil
Rose yields about 0.02 – 0.03% volatile oil
Petitgrain yields about 0.2% volatile oil
Anyone can see from this that when you have a recipe calling for a sprig (or a tablespoon) of peppermint, or rosemary it would be a lot less than just one drop of the essential oil of peppermint or rosemary.
In the food industry there are very good guidelines set out as to the maximum use levels in food and beverage products for different essential oils. If we take our list above these are the recommended maximum use levels:
Peppermint 0.104% (1040 parts per million).
Spearmint 0.132% (1318 ppm)
Marjoram 0.004% (36.2 ppm)
Rosemary 0.003% (26.2 ppm)
Rose 0.0002% (2 ppm)
Petitgrain 0.004% (37.7 ppm)
How can someone at home figure out such very small quantities when cooking at home or considering taking an oil internally? What do we have available to measure the quantities? Our dropper insert or pipette? The size of the drop obtained in this way will depend on the size of your dropper insert or pipette and the essential oil itself. Some of the thicker oils will come out slowly in bigger drops, while the more volatile ones will flow much more easily in smaller drops. How do we figure out percentages as small as 0.104% in a regular recipe?
Let us ask ourselves why are there guidelines set up at all? Is it because of flavor intensity, or because of the safety of using that oil internally, or a combination of the two? I don’t really know the answer to that question but I personally believe that the safety issues are part of the guidelines.
What about using the oils internally for therapeutic purposes? In my opinion, anyone considering using essential oils internally should know what the chemical composition of the essential oil you are considering using in this way is and what the possible cautions of those components might be. For instance ketones (found in quite large amounts in oils like peppermint 30%; spearmint 55%) generally stimulate the formation of tissue, have mucolytic effects, dissolve fats, and are potentially neurotoxic. Ketones are the most common toxic substances in essential oils. According to Dr. Penoel, ketone molecules can penetrate the blood-brain barrier more easily than other molecules. Some of the oils high in ketones can cause liver damage. After absorption from almost all regions of the gastrointestinal tract, most substances pass directly to the liver, where the great majority will be deactivated but some may be made more toxic. Not all ketones are equally problematic but this is the reason why many oils that are high in ketones carry the caution: Do not use in pregnancy. Can the developing fetus’s liver handle the ketone content of an oil like peppermint or spearmint?
I have heard some sources refer to using essential oils internally as the French Method, and using them topically on the skin as the English Method. This is actually not quite accurate. If you go to France you will be hard pressed to find a store you can walk into and just buy essential oils off the shelf for internal use. Yes there are some Medical Practitioners, both in France and elsewhere, who prescribe the internal use of essential oils, however this is generally for the treatment of severe infectious diseases and not for daily everyday use. What is generally recommended/prescribed is the use of preparations that have been carefully formulated in a laboratory and not the indiscriminate use of individual drops of essential oil. It is important to keep in mind that all recorded cases of serious poisoning with essential oils occurred after the ingestion of relatively large amounts of essential oils.
Yes there are definitely some essential oils that can be used very effectively internally, however, it is imperative that their formulation in products for internal consumption is undertaken by someone who really understands what they are working with, knows what they are doing and is able to very carefully measure out safe dosages. And even then not all essential oils can or should be used in this way.
Just because someone else tells you that they take a drop or two of an essential oil for a specific health benefit daily, or that they flavor their water with a drop of essential oil, does not mean that it safe to do so or that it will be safe for you to do so. Keep in mind that each person’s system is quite unique and individual and not everyone’s system can deal as easily with what are relatively large doses of active ingredients.
Robert Tisserand & Tony Balacs, Essential Oil Safety, Churchill Livingstone, London, 1995