Hoppy flavour in beer remains poorly understood, particularly how different yeast strains, fermentation parameters and hop varieties interact to give rise to various hop characters. Recently released hop varieties can impart novel aroma characters to beer, but the compounds responsible have not been elucidated. This paper will present results from our current research program investigating hop-derived flavour in beer and the aroma characteristics from New Zealand hop varieties.
The aim of the first study was to identify the compounds responsible for the distinct aroma characters of New Zealand hop varieties. Hop pellets from seven varieties from the 2015 harvest (Nelson Sauvin, Wai-it, Kohatu, Motueka, Riwaka, Waimea and Rakau) were analysed by gas chromatography-mass spectrometry (GC/MS) using headspace solid phase microextraction (SPME) sampling. Aroma-active compounds of interest were determined using GC-olfactometry.
The objective of the second study was to investigate the impact of yeast strain on hop-derived compounds in beer under the same conditions. Three pilot scale (~200L) worts (11.2°P, 1045 OG) were brewed with constant bittering (25 IBU) and with three different late-hopping additions at 5 min prior to flameout (Nelson Sauvin; Motueka; no hop control). Each wort was fermented with three different yeast strains at 20°C for 7 days, followed by conditioning at 4°C for 10 days prior to sampling. Samples were analysed by GC/MS using headspace SPME sampling to identify and quantify hop-derived compounds. Significant hopping regime and yeast effects were observed on hop-derived compounds, providing insights into the impact of yeast-hop interactions on beer flavour.
Dr Graham Eyres completed a PhD in Food Science at the University of Otago (2007), focusing on the identification of aroma-active compounds in hop essential oils. Dr Eyres worked in the Sensory and Consumer Science research group at CSIRO (North Ryde, Australia) from 2008-2013, investigating the physical and chemical factors that influence the sensory perception of flavour. As of December 2013, Dr Eyres took up an academic position as Lecturer of Flavour Science in the Department of Food Science at the University of Otago. The focus of current research is on flavour analysis of food and beverages, flavour generation, and understanding hop flavour in beer.