1. 2) Barth-Haas group"Hop varieties"; (http://www.barthhaasgroup.com/cmsdk/content/bhg/hop_varieties.htm)
2. 3) Hopsteiner"Hop varieties"; (http://www.hopsteiner.com/varieties.html)
3. 4) New Zealand Hops Limited. "Hop varieties"; (http://nzhops.co.nz/varieties/ndex.html)
4. 5) Yakima Chief, Inc. "High quality hops from Yakima valley"; (http://www.yakimachief.com/hopvarieties/hopvar.html)
5. 8) Tressl, R., Friese, L., Fendesack, F., Koppler, H.: Gas chromatographic-mass spectrometric investigation of hop aroma constituents in beer. J. Agrlc. Food Chem., 26, 1422-1426(1978)