Disclaimer: Please note that I wrote this in 2012, and the field has advanced considerably since then, so information might not be up-to-date!
This is part II of the mini-essay on hop science and factors influencing hop flavor and aroma in beer. The previous part (I – Introduction) can be found here. The topic for this post will be the composition of hop essential oil and how the individual major components contribute to the aroma and flavor of beer.
A gas chromatograph of the essential hop oil in Savinjski Goldings. Peaks represent different compounds present. (Source)
- Grassy and green flavors are mainly caused by aldehydes, such as hexanal and hexenal.
- Citrus flavors are mainly caused by esters (such as ethyl 4-methyl-pentanoate), nerol and linalool
- Floral and fruity flavors are mainly caused by linalool, geraniol, β-ionone, citronellol, 4-mercapto-4-methylpentan-2-one (4MMP), and 3-mercaptohexan-1-ol (3MH), as well as other ketones, epoxides and esters.
- Herbal and resinous flavors are mainly caused by myrcene, other monoterpenes, and oxidized sesquiterpenes (e.g. α-caryophyllene)
Table 1 – Major aroma compounds in hop oil (Kishimoto et al., 2006; Lermusieau & Collin, 2003; Nielsen, 2009; Schönberger & Kostelecky, 2011)
|3MH||Black currant, muscat|
|Ethyl 2-methyl-butanoate||Fruity, Apple|
|Cis-Rose oxide||Fruity, Herbal|
|Beta damascenone/phenyl ethyl alcohol||Grape tobacco, black tea|
|Various sulphur compounds||Cheesy/onion/garlic|
Even though there has been contradicting results, research seems to indicate that the hop aroma compounds can have additive and synergistic effects, and thus are not individually responsible for the different aromas found in beer. The combined effect of different hop aroma compounds can lead to lower flavor thresholds (e.g. in the case of a caryophyllene (flavor threshold of 210 mg/L) and nerol (flavor threshold of 1200 μg/L) mixture (flavor threshold of 170 μg/L) or farnesene (flavor threshold of 2000 μg/L) in a linalool mixture (flavor threshold of 500 μg/L). The transfer rate of the different hop aroma compounds between the hops and the wort/beer have been shown to vary with hop variety, and experiments have even shown that the concentration of some hop aroma compounds (such as linalool and geraniol) increase during fermentation (more on this below). The amount of hop aroma compounds carrying over to the beer from the hops, depend largely on when they are added to the wort (e.g. during boil, after boil, and even after fermentation), the temperature of the wort, the contact time with the wort, the alcohol content of the beer, and even the composition of the wort (e.g. sugar content). Hence, the types of hop aroma compounds present in a beer where the hops have been added at flameout differ from the types of compounds present in a beer where the hops have been added as dry hops after fermentation, even though the same hop variety has been used. Next is some information on the major hop aroma compounds and how they behave in wort and affect the hop aroma of finished beer.
Table 2 – Myrcene content of various hop varieties
|Hop Variety||Average oil content|
(ml / 100 g hops)
|Average myrcene content|
(% of oil)
|Average myrcene content
(ml / 100 g hops)
Structure of linalool.
Structure of (e,z)-1,3,5-Undecatriene.
Structure of 4-Mercapto-4-methylpentan-2-one (4MMP).
Structure of humulene or α-caryophyllene.
As you may notice, the essential oil in hops is complex, and there is yet no known certain composition that guarantees a certain aroma or flavor. We only covered a few of the major contributors, and missed important ones such as geraniol, citronellol and various esters. The next part will concentrate on the hop resins and bitterness in beer, and
should hopefully be finished in a week is available here.
- Ajisaka, N., Hara, K., Mikuni, K., Hara, K., Effects of Branced Cyclodextrins on the Solubility and Stability of Terpenes. Bioscience, biotechnology, and biochemistry 64 (2000) 731-734
- Briggs, D., Boulton, C., Brookes, P., Stevens, R., 2004. Brewing: Science and Practice. Cambridge: Woodhead Publishing.
- Hanke, S., Herrmann, M., Rückerl, J., Schönberger, C., Back, W., Hop Volatile Compounds (Part II): Transfer Rates of Hop Compounds from Hop Pellets to Wort and Beer. BrewingScience – Monatsschrift für Brauwissenschaft 61 (2008) 140-147
- Kaltner, D. (2000). Untersuchungen zur Ausbildung des Hopfenaromas und technologische Maßnahmen zur Erzeugung hopfenaromatischer Biere. Doctoral dissertation. Freising, Technische Universität München, Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt.
- Kishimoto, T., Wanikawa, A., Kono, K., Shibata, K., Comparison of the odor-active compounds in unhopped beer and beers hopped with different hop varieties. Journal of Agricultural and Food Chemistry 54 (2006) 8855-8861
- Kishimoto, T., 2008. Hop-Derived Odorants Contributing to the Aroma Characteristics of Beer. Doctoral Dissertation, Kyoto University.
- Lermusieau, G., Collin, S., Volatile sulfur compounds in hops and residual concentrations in beer- a review. Journal of the American Society of Brewing Chemists 61 (2003) 109-113.
- Nielsen, T., 2009. Character-impact hop aroma compounds in ale. In: T.H. Shellhammer (Ed.) Hop Flavor and Aroma – Proceedings of the First International Brewers Symposium 2007. St. Paul: Master Brewers Association of the Americas.
- Roberts, M., Dufour, J., Lewis, A., Application of comprehensive multidimensional gas chromatography combined with time-of-flight mass spectrometry (GC x GC-TOFMS) for high resolution analysis of hop essential oil. Journal of Separation Science 27 (2004) 473-478
- Schönberger, C., Kostelecky, T., 125th Anniversary Review: The Role of hops in Brewing. Journal of the Institute of Brewing 117 (2011) 259-267
- Steinhaus, M., Fritsch, H., Schieberle, P., Quantitation of (R)- and (S)-Linalool in Beer Using Solid Phase Microextraction (SPME) on Combination with a Stable Isotope Dilution Assay (SIDA). Journal of Agricultural and Food Chemistry 51 (2003) 7100-7105
- Steinhaus, M., Wilhelm, W., Schieberle, P., Comparison of the most odour-active volatiles in different hop varieties by application of a comparative aroma extract dilution analysis. European Food and Research Technology 226 (2007) 45-55
- Takoi, K., Itoga, Y., Koie, K., et al., The contribution of Geraniol Metabolism to the Citrus Flavour of Beer: Synergy of Geraniol and β-Citronellol Under Coexistence with Excess Linalool. Journal of the Institute of Brewing 116 (2010) 251-260
- Tokitomo, Y., Steinhaus, M., Büttner, A., Schieberle, P., Odor-Active Constituents in Fresh Pineapple (Ananas comosus [L.] Merr.) by Quantitative and Sensory Evaluation. Biosciences, Biotechnology, and Biochemistry 69 (2005) 1323-1330
- USA Hops, 2011, Variety Manual – Hop Growers of America (link)
- Van Opstaele, F., de Rouck, G., de Clippeleer, J., Aerts, G., de Cooman, L., Analytical and Sensory Assessment of Hoppy Aroma and Bitterness of Conventionally Hopped and Advanced Hopped Pilsner Beers. Journal of the Institute of Brewing 116 (2010) 445-458
- Van Opstaele, F., Borremans, Y., van Holle, et al., 2012, Fingerprinting of hop oil constituents and sensory evaluation of the essential oil of hop pellets from pure hop varieties and single-hop beers derived thereof. 10th Trends in Brewing