The essential oil is the active ingredient, that is to say all the components having a therapeutic effect, which is collected by steam distillation of the fresh plant. It has the smell of the plant, but much more powerful. Manufacturers sometimes distill several tons of plants to obtain one liter of essential oil (3), which explains the exorbitant price of certain oils.
Thus, a liter of essential oil such a beast as tarragon plant can cost 820 euros!
And do not be tempted by the cheap: an essential oil too cheap is necessarily low quality or "fraudulent", ie cut or mixed with other natural substances (vegetable oils, alcohols ...) or chemical (solvents, dyes, perfumes of synthesis ...).
The various essential oils utilization pathways