Determination of Hop Aromatisation of Beer by Headspace Solid Phase Microextraction in Combination with Gas Chromatography and Mass Spectrometry

Abstract

In contrast to determination of hop utilisation in terms of beer bitterness, analytical measurement of the yield of hop aromatisation is not straightforward on account of the enormous chemical complexity of hop essential oil and hoppy aroma derived thereof. In this paper, selective determination of hop oil-derived constituents in the flavour profile of pilsner beer is achieved through headspace solid phase microextraction (HS-SPME) in combination with gas chromatography-mass spectrometry (GC-MS). Highly enriched floral and spicy hop essences were prepared by density programmed supercritical fluid extraction (SFE), followed by solid phase extraction (SPE), and subsequently added in well-defined amounts to an experimental pilsner, exclusively bittered with purified iso-α-acids extract. In view of reliable measurement of the yield of aromatisation of the pilsner with the respective hop oil fractions, characteristic marker components for the floral and spicy SFE/SPE hop essences, respectively, were selected. Reliable determination of the selected markers for floral and spicy SFE/SPE hop essences in the aromatised beers turned out to be possible on condition that HS-SPME is combined with GC-MS comprising selected fragment ion monitoring (SIM). Using this approach, application of hop oil preparations can be monitored analytically, allowing improved control and specification of hop aromatisation according to the desired beer flavour. The average yield of beer aromatisation using floral and spicy hop essences was determined at about 95 %.