Fennel oil, Bitter, USA is also known as Common Fennel oil. It is obtained by steam distillation of the dried seeds. Yields range from just above two percent to nearly seven percent. Chemically it is quite similar to sweet fennel with high anethole content, up to 60 percent. However it has a spicier less-sweet aroma. Analysis of USA Bitter Fennel reveals minor components like GERMACRENE-D, methyl chavicol, camphor, and even trace amounts of menthol (probably due to wild mint in the fields). The resulting aroma is grassy-herbal and mildly sweet.