Aerts, Guido

De Cooman, Luc

De Keukeleire, Denis

Dresel, Michael

Naudts, Dirk

Praet, Tatiana

Van Holle, Ann

Van Nieuwenhove, Jan

Van Opstaele, Filip

Ghent University Academic Bibliography

Michael DRESEL1, Tatiana Praet1, Filip Van Opstaele1, Ann Van Holle2, Jan Van Nieuwenhove2, Dirk Naudts2, Denis De Keukeleire3, Guido Aerts1 and Luc De Cooman11 Flavour+ | Lab of Enzyme, Fermentation, and Brewing Technology (EFBT) | KU Leuven @ KAHOSL, Gent, Belgium; 2 De ’proef’brouwerij | R&D Department  | Lochristi, Belgium; 3 Em. Professor | UGent, Gent, BelgiumFrom Wort to Beer: The Evolution of Hoppy Aroma of Single Hop Beers produced by Early Kettle Hopping, Late Kettle Hopping and Dry HoppingKU Leuven @ KAHOSL | Faculty of Engineering Technology | Dept. Microbial and Molecular Systems (M2S) | Cluster Bio-engineering Technology (CBeT) | Gebroeders De Smetstraat 1, B-9000 Gent, Belgium | T +32 9 265 86 10 | F +32 9 265 87 24 | E michael.dresel@kahosl.be | iiw.kuleuven.be | Member of LIBRCONCLUSIONINTRODUCTIONMethodsAll beers were prepared on a semi-industrial scale (40 hl) using single-____hopping-technology with particular hop varieties (Var. A, B, Cand D). Wort and beer samples were taken at different timepoints (see Table 1) and immediately stored at -20°C untilanalysis. Semi-quantitative determinations of hop oil-derivedconstituents were performed using HS-SPME in combinationwith GC-MS operating in both full scan and selected ion-monitoring mode. The sensomics heatmap was calculatedusing the heatmap function of GENE-E (Version 3.0.12).Therefore, z-scores were calculated and the dendrogram wasconstructed by means of Kendall’s Tau agglomerative linkagealgorithm. Comparative and descriptive sensory analyseswere performed to assess flavour impressions according toDIN 10954 (1997) und DIN 10964 (1996).Knowledge of the impact of early kettle, late kettle and dry hopping on the final flavour sensation of beers is rather fragmentary. To gaininsights into the way hoppy aroma develops, samples were taken at different stages along the brewing process of single-hop beers________and analyzed using HS-SPME GC-MS, thereby aiming at accurate determination of the full spectrum of hop oil-derived volatiles. This study pinpoints analytical and sensorychanges induced by the boiling and fermentation process, as well as the influence of dry hopping.Cluster Analysis Cluster analysis (Var. D) revealed significant differences in the volatile composition of wort samples taken before fermentation and beer samples.In total 5 clusters (clusters 1- 5) that represent different compound classes can be distinguished. Cluster 5 consists of branched esters and the____terpenoids α-terpineol and α-ylangene. High concentrations of these compounds are more characteristic for the wort samples taken after late-hopping. Cluster 4 contains by far mostof the volatile compounds thereby reflecting the original hop essential oil composition. This cluster consists of characteristic estery compounds, sesquiterpene hydrocarbons andoxygenated α-humulene and β-caryophyllene derivates. High concentrations of these compounds are characteristic for the wort samples when compared with the late- and dry-hopped beers derived from the same brew. Cluster 3 contains the monoterpene alcohols geraniol and linalool as well as 2 branched esters (isoamyl propionate and isobutylisobutyrate). Clearly, these compounds are present in higher concentrations in the late-hopped wort and in the dry-hopped beer, but not in the late-hopped beer without theadditional dry-hopping step. Cluster 1 and 2 contain compounds that are characteristic exclusively for the beer samples. Besides some unknown compounds, Cluster 1 containstransformation products of terpenoids whereas the compound spectrum of cluster 2 is more diverse (esters, alcohols and β-citronellol). Sensory characteristics of the unhopped wortwere described as ‘typical wort aroma’. Early kettle and late kettle hopped worts expressed a ‘hoppy’ and ‘herbal’ aroma, which was slightly more pronounced in the late-hoppedwort. The final beers showed a typical ‘hoppy’ and ‘spicy’ flavour, whereas the dry hopped sample was dominated by floral, fruity and slightly citrussy sensory impressions.w/o hopsafter EHafter LHbeer NDbeer DH1 2 3 4 5OOneryl acetateOOOOHOO OHOOOHOOHHHOOOOH HOOOOOOOOHAcknowledgement: we would like to thank IWT Vlaanderen for financial support.The level and composition of the floral and sesquiterpenoid hop oil fraction significantly changes along the brewing process. Fermentation andcentrifugation were identified as the crucial process steps. As shown via cluster analysis, methyl esters, branched esters, terpenoids as well as_____________oxidized derivatives of α-humulene and β-caryophyllene are characteristic for early and late kettle hopped wort. Early and late hopping show an impact on absolute concentrationsbut not on the composition of hop-derived volatiles. Highest concentrations of geraniol and linalool are found in the late hopped wort. Although dry-hopping has a predominantlyquantitative influence on the volatiles, high concentrations of compounds like β-citronellol are characteristic for dry hopping. Clearly, this study proofs that dry hopping also boostsindividual volatiles which might be linked to the characteristic fruity and citrussy aroma impressions.Monitoring of Hop Volatiles along the Brewing Process04080120160conc. [ppb]sum of floral fractionABC0255075100conc. [ppb]β-myrcene levelABC0481216conc. [ppb]linalool levelABCThe level of the most volatile fraction of hop essential oil (‘floral fraction’), containing highly flavour-activemonoterpene hydrocarbons (e.g. β-myrcene), monoterpene alcohols (e.g. linalool), characteristic esters andketones, reaches maximal values just before fermentation and significantly decreases as a result of the fermentationstep (Fig. 1 A). The level of monoterpene hydrocarbons (e.g. β-myrcene (Fig. 1 B)) dramatically decreases uponfermentation while the level of other compounds such as linalool (Fig. 1 C) decreases to a lower extent. The level of‘floral’ compounds after fermentation is highly comparable to their level in the late-hopped beers (beer ND).Fig 1 A Fig 1 B Fig 1 CThe sesquiterpenoid hop oil fraction contains both sesquiterpene hydrocarbons as well as oxygenated sesqui-terpenoids and has been associated with the so-called ‘noble’ or ‘spicy’ character of hoppy aroma. The level of thisparticular class of hop oil constituents decreases significantly upon fermentation of the brews made with varieties Aand B (Fig. 2 A). However, the most crucial step leading to the loss of almost the entire sesquiterpenoid fraction iscentrifugation. The level obtained after centrifugation is equal to the level in the final late-hopped beers (Fig. 2 A-C).04080120160conc. [ppb]sum of sesquiterpenoids ABC0102030conc. [ppb]β-caryophyllene levelABC0306090120conc. [ppb]α-humulene levelABCFig 2 A Fig 2 B Fig 2 CTable 1: wort and beer sample codes and time points of samplingabbreviation time point of samplingw/o hops after 15' boiling - just before early hoppingafter EH after 75' boiling - just before late hoppingafter LH after 5' coolingbefore ferm. after 10' cooling - just before fermentationafter lag. after lagering - just before centrifugationafter centr. after centrifugationafter past. after pasteurisationbeer ND bottled beer without dry hopping;beer DH bottled beer with additional dry hopping

From wort to beer : the evolution of hoppy aroma of single hop beers produced by early kettle hopping, late kettle hopping and dry hopping

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From wort to beer : the evolution of hoppy aroma of single hop beers produced by early kettle hopping, late kettle hopping and dry hopping

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Ghent University Academic Bibliography