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The impact of hop variety and hop aroma on perceived beer bitterness intensity and character was investigated using analytical and sensory methods. Beers made from malt extract were hopped with 3 distinctive hop varieties (Hersbrucker, East Kent Goldings, Zeus) to achieve equi-bitter levels. A trained sensory panel determined the bitterness character profile of each singly-hopped beer using a novel lexicon. Results showed different bitterness character profiles for each beer, with hop aroma also found to change the hop variety-derived bitterness character profiles of the beer. Rank-rating evaluations further showed the significant effect of hop aroma on selected key bitterness character attributes, by increasing perceived harsh and lingering bitterness, astringency, and bitterness intensity via cross-modal flavour interactions. This study advances understanding of the complexity of beer bitterness perception by demonstrating that hop variety selection and hop aroma both impact significantly on the perceived intensity and character of this key sensory attribute.

9516222Highlights: Aroma modified intensity, character and temporal profile of bitterness in beer. Hop aroma modified perceived bitterness by taste-aroma interactions. Hop aroma evoked trigeminal sensations in the oral cavity. Trigeminal sensations impacted perceived beer bitterness intensity and character. Balance between aroma and bitterness levels determined bitterness character. AbstractThe effect of hop aroma on perceived bitterness intensity, character and temporal profile of beer was investigated. A hop aroma extract was added at 3 levels (0, 245, 490 mg/L) to beers at low, medium and high bitterness. Beers were evaluated for perceived bitterness intensity, harshness, roundedness and linger by a trained panel using a rankrating technique at each bitterness level, with and without nose clips. The use of nose clips enabled the olfactory aspect to be decoupled from taste and mouthfeel aspects of bitterness perception. Results showed significant modification of perceived bitterness in beer by hop aroma depending on the inherent level of bitter-ness. These modifications were mainly driven by olfaction -in an example of taste-aroma interactions, as well as certain tactile sensations elicited by the hop aroma extract in the oral cavity. At low bitterness, beers with hop aroma added were perceived as more bitter, and of 'rounded' bitterness character relative to those without hop aroma. When judges used nose clips, this effect was completely eliminated but the sample was perceived to have a 'harsh' bitterness character. Conversely, at high bitterness, even when nose clips were used, judges still perceived beers containing hop aroma to be more bitter. These increases in bitterness perception with nose clips indicates the stimulating of other receptors, e.g. trigeminal receptors by hop aroma extract, which in tandem with the high bitterness, cause perceptual interactions enhancing bitterness intensity and also affecting bitterness character. Bitterness character attributes such as 'round' and 'harsh' were found to significantly depend on bitterness and aroma levels, with the second level of aroma addition (245 mg/L) giving a 'rounded' bitterness in low bitterness beers but 'harsh' bitterness in high bitterness beers. The impact of aroma on temporal bitterness was also confirmed with time-intensity measurements, and found to be mostly significant at the highest level of hop aroma addition (490 mg/L) in low bitterness beers. These findings represent a significant step forward in terms of understanding bitterness flavour perception and the wider impact of hop compounds on sensory perception.

Changes in hop-derived compounds of beer were evaluated over 10 months of storage at 3 and 20°C, revealing significant changes in the beers stored warm. Beer pH and colour increased, together with 'hop creep' through storage of unpasteurised dry-hopped beers. Hop bitter acids decreased moderately during storage at 20°C but not at 3°C and hop aroma compounds -key contributors to dry-hop flavour -were significantly depleted upon warm storage. Cold storage resulted in significant retention of these compounds in the beers, especially hop mono-and sesquiterpenes which exhibited the greatest losses after warm storage. The losses of hop aroma compounds were linked in part to association with polymeric crown cap liners ('scalping'), the dynamic of which was further impacted by storage temperature. A wide range of hop aroma compounds were found to be abundant in the crown cap liners of bottled beers after storage, in contrast to canned beers which showed better retention of key hop aroma compounds (caryophyllene, myrcene and humulene) throughout storage. The impact of some of the chemical changes during storage was determined by sensory analysis. Changes in 'bitter', 'tropical' and 'citrus' fruit, 'sweet' and 'malty' attributes were all influenced by storage temperature and the given beer. Changes in 'floral', 'fruity', 'sour/acidic', 'alcoholic' and 'lingering aftertaste' were dependent on the beer, whilst changes in 'spicy' notes were dependent on storage temperature. These findings provide meaningful insights into the storage induced changes of dry-hop flavour in dry-hopped beers.

A single‐run reverse phase‐high performance liquid chromatography method for the quantification of humulinones, α‐acids, iso‐α‐acids and reduced iso‐α‐acids (where present) in commercial beer samples is presented. The method utilizes a binary solvent system consisting of (A) 1% v/v acetic acid and (B) 0.1% v/v orthophosphoric acid in acetonitrile. Separation was achieved on a Purospher® star RP‐18 column (250 × 46 mm, 3 µm) with a flow rate of 0.5 mL/min. The compounds of interest eluted within 32 min. The method was fully validated according to International Conference on Harmonization guidelines and subsequently applied to monitor degradation of hop acids in a storage trial where four lager beers were aged at 28 and 38 °C for 70 and 60 days, respectively. Results confirmed the widely reported degradation through storage of trans‐iso‐α‐acids whilst demonstrating that the HLPC method was sufficiently sensitive to monitor and model this degradation. One beer exhibited a significantly lower (P < 0.05) rate of trans‐iso‐α‐acid degradation than the other conventionally hopped beers in the study, which might have been linked to its higher pH (4.71 vs 4.36). The relative stability of reduced iso‐α‐acids during ageing was also confirmed.