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Comprehensive Characterisation of the hop-derived Sesquiterpenoid Fingerprint of American Kettle hopped Lager Beers
T. Praet, F. van Opstaele, J. Baert, G. Aerts, and L. de Cooman

In common brewing practice the typical so-called kettle hoppy aroma of lager beer results from the addition of aroma hop varieties to the boiling kettle. Years of extensive research has elucidated that hop-derived volatile flavour-active oxygenated compounds are most likely to impart this kettle hoppy aroma. In particular the oxygenated sesquiterpenoids are considered to play a key role in the spicy and herbal impression of ‘kettle hoppy’ aroma of traditional kettle hopped lager beers. However, accurate analytical detection and identification of these compounds in lager beers is everything but straightforward since these compounds are mostly present at the low ppb level. Therefore, in this study, three American kettle hopped lager beers expressing clear hoppy aroma characteristics were analysed via HS-SPME-GC-MS to obtain hop-derived volatile profiles. A relatively simple methodology using Solid Phase Extraction (SPE) was developed to enrich the hop oil volatiles, in particular the oxygenated sesquiterpenoids, present in beer and to distribute them over different fractions to overcome the analytical problem of co-elution. After analysis of these fractions, a remarkable number of 63 compounds was detected in the chromatographic region of interest. Amongst the 41 tentatively identified compounds, 33 proved to be oxygenated sesquiterpenoids. We also report for the first time the presence of iso-korajol and 3 caryophyllene derivatives, i. e. 4S-dihydrocaryophyllene-5-one, 6(5→4)-abeo-8,12-cyclo-caryophyllan-5-al and 6(5→4)-abeo-caryophyll-8(13)-en-5-al in lager beer. In addition, olfactory assessment via GC-O sniffing analyses was performed on the SPE-derived fractions of a lager beer, exclusively hopped with noble aroma hop varieties. Flavour-active zones were frequently allocated to α-humulene and β-caryophyllene derived epoxides and alcohols, sustaining the general view that these compounds might indeed play a key role in kettle hoppy aroma.

Descriptors: lager beer, hops, flavour-activity, hoppy aroma, oxygenated sesquiterpenoids, HS-SPME-GC-MS

BrewingScience - Monatsschrift für Brauwissenschaft, 67 (November/December 2014), pp. 183-194