Hydro distillation, or steam distillation, is often used to extract volatile compounds. Hydro distillation uses steam that permeates the plant containing the desired terpenes. After the steam passes through the plant bringing along the terpenes, the steam is then condensed, creating a water and terpene distillate mixture. The the water is then drained, only leaving the terpene distillate.
Vacuum distillation is an offshoot of Hydro distillation, but offers a much more sensitive extraction method. Vacuum distillation lowers the boiling point of the water used in steam distillation by sucking out part of the atmosphere in the distillation set up. This maintains lower pressure and provides a more pure, less warped terpene.
In a study done by the University of Kentucky, Lexington, researchers explored how to collect terpenes already emitted into the atmosphere by plants. The scientists took a live plant and placed it into a gas chamber. They then had a flow of air entering the chamber and a vacuum line extracting gasses from the chamber. The outgoing gasses were passed through a tenax resin packed pipette to trap the terpenes. The pipettes were changed every couple of hours and the terpenes were then pulled from the resin.