Tag Archives: dry hop

Linalool – Fresh and Floral Hop Aroma

Linalool has a rather prominent, but at times contested, place in hop aroma. Over the past several years, many brewers and research groups have attempted to use it as a marker in the assessment of the qualities and quantities of hop aromas, both in the hop field and in the beer bottle. Other investigators have been hesitant to distill the representation of such a complex phenomenon as hop aroma into a single compound, and have downplayed its usefulness as a chemical marker. Nevertheless, linalool is an influential part of hop aroma in many varieties and, depending on hopping regimes, in finished beers as well. Here, we’ll discuss the importance of this aromatic compound in hops and brewing.

Linalool is a terpene alcohol, and is closely related to myrcene, being its hydration product.  It is found in dozens (if not hundreds) of plants, flowers, and spices, but in freshly dried hop cones it is generally found at levels of about 25-150ppm (mg/kg).  Due to the ability to have two configurations at the #3 carbon, linalool is found as two stereoisomers (S, R), each having different thresholds and aroma qualities:  S-linalool has a sweeter, more floral aroma and an odor threshold of about 7ppb, while R-linalool has a wood, spicy, and lavendar-like character and a much lower threshold at less than 1ppb.   Regardless of the total level of linalool in a hop variety, the ratio of these stereoisomers in fresh hops seems to be fairly consistent:  about 93% of it is in the R form.  Generally, linalool’s threshold in beer is much higher – upwards of 100ppb  (2.2 and 180ppb, for R and S respectively).   The pure linalool that I use in my sensory department (which I have to assume is a mixture of isomers) has a very pleasant sweet, tropical, fresh floral character, but is also not unlike the aroma of Froot Loops® cereal.   To be honest, it’s one of the most pleasant aromas I’ve ever smelled, which is probably why it’s a very popular addition to many fragrant commercial products, from perfumes to laundry detergents.   Apparently, it’s so pleasant smelling that it has been shown to reduce stress levels in laboratory rats and inhibit the activity of genes associated with stress hormones.

Despite having an aroma that is only remotely reminiscent of hops, linalool is widely accepted as one of the few compounds that directly contributes to hop aroma in beer.  Being a volatile flavor-active compound, however, the presence of linalool in beer hinges greatly on a number of factors.  Not surprisingly, the variety of hop plays a crucial role in the amounts of linalool available for the beer, but also the growing conditions and the maturity of the plant at harvest time.  Some research breeders have considered using linalool as a way to gauge the readiness of a crop for harvest.  Apart from variety, growing conditions, and maturity, production processes in the brewery have the biggest impact on linalool levels in the beer.  The sweet and floral aroma characteristics of linalool are quite distinct from the hop aromas generated by the noble hop varieties favored by many European brewers, but this is not necessarily due to the varieties themselves (although they do tend to be lower in levels relative to the newer American aromatic hops).   More influential is how these nobel hops are often used in such beers, and that is often via “kettle hopping”, where noble aroma hops are added near the beginning of the boil.  Despite most of the hop essential oils being lost via steam distillation throughout the boil some hop aromas must remain, as this kettle hop aroma is generally described as spicy, woody, and herbal – terms which are obviously not malt-related.   But these aromas are also dissimilar to that of linalool, which must be lost with the rest of the essential oils.  As one might expect, European kettle hopped beers have very low levels of linalool and “sweet, fresh, and floral” hop aroma terms are not associated with these beers.

So, just like hop aroma in general, in order to get more linalool in the beer, one would need to add hops later in the boil so that not so much is lost via distillation.  “Late hop aroma” is imparted by adding hops at kettle knockout or in the whirlpool.  This is where you really begin to notice the impact of some of the essential hop oils, leading to various aromas like citrus, piney, floral, perfume, etc.   The later the addition (ie, the closer to wort chilling) the more linalool will remain in the wort.  Some research has demonstrated that when adding hops at 10 minutes prior to the end of boil, linalool levels can rise from about 8ppb to 60ppb before tailing off near 30ppb by the end of boil.   By contrast, adding the hops just 2 minutes before the end of boil, linalool levels can rise to 85ppb before stabilizing at about 80ppb.   Even without any indication as to what hop variety was used or other parameters, this is a dramatic demonstration of the importance of timing with regards to hop additions.

As you probably already know, dry hopping is the best way to get the elusive hop aroma into beer in significant amounts.  But, interestingly, research has shown that this doesn’t necessarily apply to linalool.  While some linalool may be imparted by dry hopping, it seems that it is rather negligible compared to late kettle hopping.  In addition, many of the other aromatic compounds contributed to the beer during dry hopping (such as methyl esters and ketones) will likely mask the presence of linalool to the point that it would be difficult to detect.

The final way that linalool is introduced to beer is via glycosides (which I’ve discussed before).  Glycosides are interesting because they can carry aromatic compounds into the beer rather surreptitiously and release them under various circumstances.   A glycoside is essentially a sugar molecule which is bound to another molecule at its #1 carbon position, and in such a configuration they are not flavor-active.  However, during fermentation, yeast enzymes break this bond and release the aromatic molecule.  Some of these glycosides contain linalool as the aromatic compound.  It’s not always enzymes that are needed to cleave these molecules in twain;  sometimes an acidic environment is all that is needed.  In fact, glycosides also play an important role in wine flavor, as wine is quite acidic.   But while most beer not as acidic as wine, acid hydrolyzed glycosidic cleavage reactions still take place in beer.   It’s been shown that if glycosides survive into the finished beer, they can continue to release linalool as the beer ages, and depending on what kind of hop product is used and other production parameters, this source of linalool may actually be more influential to beer flavor than the linalool which comes from the hops directly.  I’d really like to delve a little deeper into glycosides and how they are introduced and modified throughout the brewing process, but besides the little bit of research I’ve found regarding them, all the references I can find now are in German…  and I don’t speak German.  If anyone knows of any papers about glycosides and beer flavor, please let me know.

And, for now, that’s all I have to say about that.  I think the next posts will be about some beer we’ve drank recently.

See you next time!


Peacock, V., “The Value of Linalool in Modeling Hop Aroma in Beer”, Master Brewers Association of the Americas Technical Quarterly, 47:4, 2010, p.29-32.

Kaltner, D., Mitter, W., “Changes in Hop Derived Compounds During Beer Production and Aging”, Hop Flavor and Aroma:  Proceedings of the 1st International Brewers Symposium, MBAA 2009, p.37-47.

Myrcene: the Green Giant of hop aroma

And we’re back!

Myrcene chemical structure

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 0.13ppmppb, while beers which were hopped after wort cooling had about 66ppmppb – 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.