Therapeutic-grade essential oils are most often extracted via a low-heat steam distillation process in which steam is circulated under pressure through plant material liberating the essential oils into the steam. As the steam mixture cools, the water and oils naturally separate and the oil is collected in its pure form. To ensure the highest quality oil extract of correct chemical composition, temperature and pressure must be monitored very closely. Too little heat and pressure will not release valuable oil while too much can change an extract's composition and potency. As important as the carefully controlled extraction process is, the careful selection of the correct plant and plant parts harvested at the right time is also required for a successful extraction. This complex process is as much art form as it is science and requires experienced growers and distillers working together to ensure a quality product.
(Fact: It takes as much as 12,000 rose blossoms to distill 5 ml of therapeutic- grade essential rose oil.)
Steam distillation is by far the most common method of extraction, but some oils such as citrus oils are extracted through a process of compression in which the oil is squeezed from the plant. A very few essential oils are extracted using solvents that bind with the oils and are later removed from the final product.