Characterization of the citrus character of hops via gas chromatography-mass spec/olfactometry

With the emergence of craft brewing, the popularity of intense hoppy beer styles and breeding of new flavor hop varieties (with high oil contents and intense hop character) has increased. Hop citrus character is currently poorly characterized and therefore the objective of this study was to identify the odour-active molecules of citrusy hop oil fraction, in an attempt to investigate the relationship with the citrus character of some commercial hop varieties. We report in this work the results achieved in characterizing citrus hop character and the relevance in terms of production of commercial hop product fractions available to brewers. Hop essential oils were obtained from several varieties by steam distillation. The sensory profile of these hop oils was determined with the selected varieties divided in two groups; ‘citrusy’ and ‘not-citrusy’ hops. Volatile compounds were determined using reference compounds. Solid Phase Extraction (SPE) was used to fractionate hop essential oil, using a C18 column stationary phase. Hop oils, suspended in an ethanol/water solution, were pipetted on the C18 column and eluted to allow hop oil compounds to be adsorbed into the stationary phase. The adsorbed compounds were selectively desorbed and pipetted into a range of ethanol/MQ-water solutions and the effluents collected. The hop oil fractions were analysed by HS-SPME-GC-MS and Cluster analysis (Ward’s Method, Squared Euclidean) and Principal Component Analysis (PCA) were carried out. Sensory and chromatographic analysis of the varietal hop oils highlighted the citrusy hop character in specific fractions. The fraction 70/30 was selected for further analysis. Considerable differences in the qualitative and quantitative composition between the hop varieties were found by the GC-MS analysis of the 70/30 fraction. Analysis of citrus character in varietal hop essential oil was determined for several varieties with citrus intensity in the hop cones. These were compared and contrasted with non-citrus hop and citrus fruits. Cluster and PCA analysis highlighted the role of geraniol in citrus character. This project has identified initial practical benefits for the Hop Industry, namely the screening for citrus character of new hop varieties being bred, the ability to compound hop oil fractions to create citrus intense fractions, and to increase our understanding of hop citrus character and the synergistic effects of geraniol rich compounds in citrus intensity.status: publishe