Impact of Yeast Strain and Fermentation on Perceived Hop Flavour in Beer

The main objective of this thesis was to determine the effect of yeast strain and fermentation on the sensory perception of hop flavour in beer. This project evaluated the differences between 12 different yeast strains on the flavour perception of a standardized wort made using bittering hops (Simcoe) and late-hopped with one aroma hop (Motueka). The yeast selection was a range of ale (S. cerevisiae), wheat beer (S. cerevisiae), lager (S. pastorianus), wine (S. cerevisiae wine yeast hybrid), Chardonnay (S. cerevisiae) and Champagne (S. bayanus) yeast strains. The beer was then evaluated by sensory analysis using a free sorting task methodology. A panel of 14 subjects including trained, untrained and beer experts were recruited for the study. The 12 beer samples were evaluated in triplicate over three separate sessions to form groups according to the similarity of their sensory attributes, with descriptors allocated to each group. The beer sorting task data was analysed using multiple correspondence analysis (MCA) and a frequency table (contingency table) to understand the sensory attributes driving the differences between the beer samples. The top five most frequently used attributes were hoppy, fruity, sulphury, bitter and citrusy. Based on a textual analysis of the sensory attributes generated per beer sample, the significant sensory attributes associated with specific beer samples were determined. The beer fermented with 34-70 yeast was associated with a hoppy flavour, whereas both OTA 79 and Wy-1272 beers were significantly related to sulphury. Spicy flavour notes were significantly associated with WB-06 and WLP 730 beers, and estery was also significantly associated with the WLP 730 beer. VIN 13 beer was significantly related to sour and metallic, whereas WLP 001 beer was significantly related to astringent. The projections illustrated all beer samples were considerably different and this was due to differences in yeast strain used to ferment the 12 samples. Volatile analysis in beers was carried out using headspace solid-phase microextraction (SPME) and gas chromatography mass spectrometry. From the volatile analysis a total of 102 volatile organic compounds (VOCs) were detected, including terpenes, esters, alcohols and phenols, of which 77 VOCs were significantly different between beer samples (p-value