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Comparison of the Analytical Profiles of Volatiles in Single-Hopped Worts and Beers as a Function of the Hop Variety
M. Dresel, T. Praet, F. Van Opstaele, A. Van Holle, D. Naudts, D. De Keukeleire, L. De Cooman and G. Aerts

Being one of the most consumed beverages in the world, much effort has been made to reveal the structures responsible for the sensorial characteristics of beer. Yet, the knowledge on the precise contribution of hop-derived volatiles towards the hoppy aroma of beer is rather fragmented. For a long time, the aroma of fresh beer was believed to be mainly imparted by single compounds. However, increasing evidence showed that sensorial perception of the hoppy aroma of beer is more complex than originally assumed. Moreover, the factors responsible for the perceivable differences originating from distinct hop varieties used for late and dry hopping have not been fully revealed. In order to understand how the choice of the hop variety affects the final aroma of beer, we investigated in a previous study with four different hop varieties how the analytical composition of the volatile fraction changes throughout the brewing process and how that affects the composition of late and dry hopped beers. However, the analysis of four different hop varieties arose more questions. Therefore, in this study, we studied 15 other hop varieties during different stages along the brewing process of single hopped beers and analyzed wort and beer samples via headspace solid-phase micro extraction and gas chromatography-mass spectrometry (HS-SPME GC-MS). Additionally, the profiles of the corresponding hop varieties were determined. This enabled the accurate determination of both the full spectrum of hop oil-derived compounds as well as of the higher esters and higher alcohols produced during fermentation. Our investigation reveals substantial changes in the volatile patterns of the wort and beer samples, in comparison with the selected hop variety, which arose from the boiling and fermentation processes, as well as the applied late and additional dry hopping techniques. Concentrations of the “floral” (e.g. oxygenated fraction of total hop essential oil composed of monoterpene alcohols, esters, ketones and aldehydes) and the sesquiterpenoid hop oil fractions changed significantly along the brewing process. As expected, concentrations of saturated esters and higher alcohols in beers were shown to be mainly influenced by the fermentation and not by the hop variety. Although the concentrations of practically all other compound classes (especially of linalool and geraniol as the most important monoterpene alcohols) were higher in the dry hopped beers, dry hopping does not affect the original intrinsic qualitative composition of hop oil constituents. Yet, substantial quantitative changes were observed. Furthermore, special attention was paid to the influence of additional dry hopping on the transfer behavior of selected hop derived-monoterpene alcohols. Transfer rates for linalool were comparable for all 15 hop varieties, whereas the transfer rates for geraniol differed significantly which indicates that the selected hop variety is of major importance.

Descriptors: hops, beer, sesquiterpenes, volatiles, GC-MS, Humulus lupulus

BrewingScience – Monatsschrift für Brauwissenschaft, 68 (January/February 2015), pp. 8-28