Session Chair:
Filip Van Opstaele (Manager of the analytical centre of EFBT, KU Leuven, BE)
Application of atmospheric pressure chemical ionization gas chromatography-mass spectrometry (APGC-MS) to assess hop aromatic quality, terroir effects, and harvest maturity
By Nils Rettberg et al., VLB / TUB
From a brewers perspective minor hop volatiles (terpenoids, esters, ketones, acids, and S-compounds) appear of primary importance. They are well extracted when dry hopping, are transformed by yeast (enzymes), and impact beer flavor in very low quantities (ng/L-µg/L). The analysis of these volatiles is challenging, yet the search for analytical assays enabling effective qualification/quantification is ongoing. In the current study APGC-MS was evaluated for its use in hop volatile analysis. First, a suitable APGC-MS method was developed and the ionization parameters were optimized to yield maximum (protonated) molecular ion intensities. Successful validation was done by comparing quantitative data of 15 major hop volatiles as determined by EBC 7.12 and APGC-MS in >150 hop samples from >50 varieties. Most importantly, to evaluate the performance of APGC-MS to detect, identify, and quantify minor hop volatiles the method was applied to a unique sample set which was originally collected to study the effect of variety, maturity, and farm on hop quality metrics. By doing so, the ability of APGC-MS to enlarge the current understanding of hop chemistry is demonstrated.
Boosting release of hop-derived thiols with interspecies hybrids
By Kistoffer Krogerus et al., VTT
Interspecies hybridization has been shown to be a powerful tool for developing and improving brewing yeast in a number of industry-relevant respects. Thanks to the popularity of heavily hopped IPA-style beers, there is an increased demand from brewers for strains that can help boost hop aroma and reduce the cost impact of high hopping rates. Here, we explored whether hybridization could be used to construct strains with an enhanced ability to release hop-derived flavours through beta-lyase activity, which releases desirable volatile thiols. Wild Saccharomyces strains were shown to possess high beta-lyase activity compared to brewing strains, however, they also produced phenolic off-flavours (POF) and showed poor attenuation. To overcome these limitations, interspecies hybrids were constructed between three brewing and three wild Saccharomyces strains (S. uvarum and S. eubayanus). Hybrids were screened for fermentation ability and beta-lyase activity, and selected hybrids showed improved fermentation and formation of both volatile thiols (4MMP, 3MH and 3MH acetate) and aroma-active esters compared to the parent strains. Undesirable traits (e.g. POF) could be removed by sporulation.
Yeast and Enzymatic Release of Odorant Polyfunctional Thiols from Cysteinylated and Glutathionylated S-Conjugates
By William Donck et al., UC Louvain
In hops, 41 free polyfunctional thiols (PFTs) have been evidenced, including many sulfanylalkyl alcohols and their corresponding esters. More recently, besides the free forms, cysteinylated (Cys-) and glutathionylated (G-) adducts of PFTs have been identified in various hop cultivars at much higher concentrations. The release of PFT’s from Cys-adducts can be performed in several ways, including through primary fermentation by yeast. Incubation with apotryptophanase is also a solution to release free PFTs. Finally, chemical reactions during boiling and aging are able to release free forms of PFTs. Yet the release of PFTs from G-adducts has been less studied so far, despite their higher concentrations in hops. Two main strategies are currently investigated: either by using only selected yeasts or by incorporating exogenous enzymes. Enzymes such as gamma-glutamyl transferase are able to transform G- into Cys- adducts. In the present work, selection of efficient yeast strains (alone or mixed) and optimization of the primary and secondary fermentation parameters (wort density, temperature, duration, tank shape ..) will be investigated.
Development of thiols and thiol precursors in different hop varieties during hop harvest and their impact on beer flavor
By Christina Schönberger¸ BarthHaas
Thiols are sulfur containing aroma compounds that can exhibit, due to their very low aroma threshold, strong fruity flavors in dry hopped beers. In brewing, available scientific data is scarce. However, thiols are known to be hop variety specific. Their analysis is challenging, and the sensory importance is not unequivocal proven. We have investigated 5 different hop varieties. We have found that free thiols behave variety specific over harvest time and that the terroir effect is less important. We have also found that precursor structures decrease over harvest time with no increase in free thiols in the harvested hops. Benchtop fermentation trials and different dry hopping trials using different yeast strains show a very low impact of fermentation and dry hopping on the generation of thiols. Although both analytical and sensory data confirm the importance of the choice of a suitable combination between yeast strain and wort quality on flavor profile, sensory data shows a very low correlation with analytical data of free thiols. Further research needs to investigate the importance of wort composition to increase the potential of thiol release in brewing.