Peppermint oil is steam distilled from the flowering tops of the perennial herbs, Mentha piperita or Mentha arvensis (aka cornmint). The principal constituents of peppermint oil are menthol and menthone with lesser amounts of menthyl acetate and menthofuran among others. Piperita is mostly cultivated in Western USA (some production in India), with the bulk of arvensis from China and India.
The arvensis plant distillates are particularly rich in menthol. This is extracted in varying degrees during production resulting in different grades of peppermint oil, graded by percentage menthol.
Peppermint essential oil is a pale yellow, yellow/green to colourless liquid with a penetrating characteristic minty camphoraceous odour.