And we’re back!
Myrcene is an aromatic hydrocarbon which is an important part of the essential oils of a number of different plants, most notably hops. In perfumery, it is used as an intermediate in the production of various aromatic compounds like geraniol, nerol, and linalool. In brewing, it is considered the headlining feature of the “green hop aroma” and is often found in many dry-hopped beers. It has an odor which is described as “herbaceous, resinous, green, balsamic, fresh hops, and slightly metallic” and can be quite pungent at higher levels sometimes smelling a bit like floor-cleaner. In water its odor threshold is about 14ppb, but it is a good deal higher in beer. While it is found at very low levels in kettle-hopped beers, its high volatility and low solubility in aqueous solutions means that it doesn’t tend to stick around very long during the kettle boil. In fact, some studies have shown that myrcene levels in beers which were hopped at the beginning of the boil are around 0.13
ppmppb, while beers which were hopped after wort cooling had about 66 ppmppb – a 508x difference! Myrcene is also readily oxidized and there are some ideas that if it doesn’t volatilize up and out the kettle stack, then it probably degrades and leads to a handful of other aromatic compounds.
Cascade hops tend to be regarded as the classic “myrcene hops”, and in fact it makes up roughly 50-60% of the total hop oil fraction of Cascades. Some hop varieties do have higher levels of myrcene than Cascades, however. Amarillos (~70%), Citra (65%), Crystal (40-60%), Horizon (55-65%), Simcoe (60-65%) and others can have higher levels than Cascades. Conversely, most of the European Noble hops have some of the lowest levels of myrcene: Saaz (5-13%), Hallertau Mittlefrueh (20-28%), and UK Fuggle (24-28%) are among the lowest. Keep in mind, however, that geography, growing conditions, and storage conditions all play a part in dictating myrcene levels. The same study mentioned above showed that a post-wort-cooling hop addition with hops aged at 40C for 30 days yielded myrcene levels of 0.82ppm (as opposed to the 66ppm with cold-stored hops). As with most other aspects of hop quality, there is a difference between whole hops and pellets as well. Whole hops can have as much as 70% more myrcene than pellets of the same variety, but that difference is flipped when the wort is hopped as only 5% of myrcene is extracted from whole hops compared to 17% from pellets.
(note: there are some discrepancies in the literature regarding myrcene levels in Hallertau Mittlefrueh, with some levels reported to be around 10-30% of the total oil fraction, while another study has found higher levels of myrcene in Hallertau MF than in Cascade hops. Since more sources are reporting that H.MF has very low levels compared to most other hop varieties, that is the idea I would stick under most circumstances).
Kishimoto, T., Investigations of Hop-Derived Odor-Active Compounds in Beer, Hop Flavor and Aroma, Proceedings of the 1st International Brewers Symposium, 2009, pg 49-58
10/24/12: An EDIT that took too long to initiate: fixed myrcene levels from ppm to ppb.