Don't you know, a visible ring of residue which appears after the essential oil has dried, is an indication that the oil has been diluted with a carrier oil. Given its volatile nature, pure essential oils do not leave any residue when it dries. Pure essential oils do not feel greasy or oily, and they never should.
Organic Commercial Food-Grade essential oils are also used as a means of extracting essential oils. In this process, used, for example, to extract the onion, garlic, wintergreen and bitter almond essential oil, the plant material is macerated in warm water to release the volatile compounds in the plant.