Extraction of Hop Oil
The most common way to extract hop oil is by using a steam distillation method. Freshly dried hops (Figure 1) are best to use for direct steam distilling, so that the steam can penetrate the hop flower much easier (Guenther -V.6, 1949). The rate of distillation must be controlled carefully because of the fragility of the hop components.
Source:http://www.wsu.edu/~gmhyde/433_web_pages/433Oil-web-pages/essence/essence-oils.html
