Terpenes are the molecules in hops that give hops their unique aroma: citrusy, floral, earthy, piney, etc. Individual terpenes are not unique to specific hop. However, the ratios of several terpenes allow us to interpret the primary and secondary aromas differently. We use supercritical CO2, not liquid, not gas, not solid, but somewhere in between those to extract the terpenes from hops.