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).
IndieHops, In Hop Pursuit Blog, Hop Oil: Is Bigger Better? A Preview of Ongoing Research at OSU
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.
Interesting post. Any thoughts on fiddling with temperature to maximize myrcene levels beyond just full boil v. dry hop? I forget the temp at which this volatilizes (160F??) but would there be any benefit in doing a late addition to the whirlpool to try to maximize this compound? I’m just thinking solubility would be up at those temps. Not worth the trouble? What do you think?
Myrcene boils at about 167C (not F), but it volatilizes at every temperature from its freezing point up to boiling (more so the higher you go obviously). And while solubility may be slightly elevated with the higher temperatures in the whirlpool, I doubt it would be enough to make much difference. It seems the best way to get it into the beer is by dry-hopping or some other cold-side addition where exposure time and ethanol would assist the process.
“with hops aged at 40C for 30 days” … wouldn’t myrcene degrade into nothingness by then? most brewers dry hop 3-6 days max
Have you come across any work which has looked at the potential for metabolism of myrcene by brewers’ yeast in dry hopped beers? Structurally it looks like it has good potential for biotransformation into some interesting flavours.
Yeast cells are also capable of partitioning hydrophobic compounds so while the compound may be exceed its solubility limit in beer it may well partition into the yeast and deliver flavour in that way.
That’s pretty interesting Bill. I haven’t seen any research about that, but I’ll start looking. If you know of any, let me know.
A quick look to see about myrcene metabolism has given some answers. It appears that under this study no myrcene was detected within cell bodies, but the people conducting this study did not dry-hop to give large amounts of myrcene, so it may have been below limits of detection especially considering the low solubility of myrcene. I cite this study
Biotransformation of hop aroma terpenoids by ale and lager yeasts, Andrew J King, J.Richard Dickinson, FEMS yeast research, March 2003
Thanks for the info Trevor.
I love this blog.
Do you know what does mycrene oxidize or degrade into? I have been trying some old IPA’s and I’m curious if that signature mycrene aroma foes away to reveal other compounds, or develops into something else altogether.
I’d like to second Flagonofale’s question. I’d be very interested in your (or other peoples) opinions about the likely degredation products of myrcene exposed to heat, but not allowed to volatilize away.
Hey Thirstyboy and FlagonofAle,
Sorry I’ve taken so long to address this, but what I’ve found so far (not much) is that myrcene can degrade into linalool, geraniol, and geranyl isobutyrate, among many other things I’m sure. These flavors are also normal parts of hop aroma, so while the myrcene intensity will drop after packaging (or disappear) it may be replaced to some extant by some of these other flavors.
More info can be found here (but I haven’t found the whole article yet):
“Autoxidation of some constituents of hops. I. Monoterpene hydrocarbon, myrcene”
Robert H. Dieckmann, S. Rao. Palamand
J. Agric. Food Chem., 1974, 22 (3), pp 498–503
Publication Date: May 1974
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