Investigating the contribution of hop components to the perception of beer flavour

Considering the substantial amount of research that has been published in the field of hop science during the last decades, very little is known with regard to the multimodal flavour perception of hop-derived volatiles that not only contribute to the pleasant ‘hoppy’ aroma and flavour, but are also involved in other sensations of gustatory and trigeminal origin perceived in beer. The aim of this research was to further understand the sensory complexity of Magnum hop essential oil and scCO2 hop oil fractions extracted therefrom. This PhD project combined static and dynamic sensory techniques, an established gas chromatographic method, and comprehensive statistical analyses to investigate the relationship between hop volatile compounds and their sensory characteristics (quantitative and qualitative) in different matrices. The olfactory, gustatory and trigeminal differences between five hop oil fractions representing the main chemical classes of Magnum hop oil were determined in a simple model solution (4% ABV) using a newly established attribute lexicon and following a Quantitative Descriptive Analysis (QDA) approach. The fractions induced a range of different aroma and flavour sensations, which could partly be attributed to specific hop aroma compounds. The most polar compounds in the terpene alcohol fraction were suggested to be responsible for cross-modal interactions eliciting both aroma and/or taste and trigeminal sensations. A peppery tingling mouthfeel was perceived, which is assumed to be a sensation innervated by the trigeminal nerve. The terpene alcohol fraction was further categorised into monoterpene alcohols (i.a. geraniol, linalool) assumed to be mainly responsible for olfactory sensations and sesquiterpene alcohols (i.a. humulol, humulenol II) to foremost induce gustatory and tactile sensations. Further fractionation specifically targeting single compounds and compound groups (sub-fractions) that were added to a commercial lager beer base (4.5% ABV) to measure the impact of perceptual interactions between compounds and the beer matrix using a revised attribute lexicon and adjusted dosage rates. A clear cause-effect-relationship could be located between geraniol and the sweet taste perceived in the beer. Geraniol also induced a smooth bitterness, which was opposed by the harsh bitterness quality added by sesquiterpene hydrocarbons. Linalool was classified as a aroma/flavour ‘enhancer’ rather than individually contributing to the sensory profile. Significant effects on lingering mouthfeel sensations remained absent, which illustrated the need for temporal sensory assessments to adequately and holistically discriminate the samples with regard to these sensations. A Temporal Check-All-That-Apply (TCATA) by modality approach was used to assess multiple sensory characteristics of selected hop flavour products perceived simultaneously. The products contained the previously studied hop oil fractions and were combined with either iso-alpha-acids or oxidised beta acids (hulupones) in a lager base beer brewed without any hop materials. Bitter acid extracts were found to significantly affect the duration and sensory profiles of the hop flavour products in the beer suggesting a sensory interaction induced by the co-occurrence of hop aroma compounds and hop bitter stimuli. Lingering sensations (peppery tingling, astringency) were foremost found to significantly discriminate between the samples at the end of the evaluation period (>2min). Since temporal sensory data is inherently noisy, a part of this research included the examination of TCATA data pre-processing approaches using comprehensive statistical analyses. This revealed that time standardising the TCATA by modality data could not remove inter- and intra-individual variation between the panellists and thus, not improved the quality of the sensory data. This research has provided new and in-depth knowledge on the sensory properties of scCO2 hop oil fractions, sub- fractions, and key compounds extracted from Magnum hop. Moreover, different sensory characterisation strategies and tools are presented that captured the fine nuances of the sensory profiles of these hop extracts. The findings demonstrated the involvement of hop volatile compounds in sensory interaction effects causing multi-modal profiles in beer. Their ability to modify gustatory and trigeminal sensations should be considered for future developments of flavour preparations