A novel gas chromatographic system to characterize hop aroma

Analytical Session
Andrew Tipler, PerkinElmer, Shelton, CT, USA
Co-author(s): Lee Marotta and Tom Kwoka, PerkinElmer, Shelton, CT, USA

ABSTRACT: The flavors of many beers are greatly affected by the addition of hops at different stages during the brewing process. Aroma plays a very important part in the tasting experience. Hops contain many volatile organic compounds (VOCs) that contribute to the aroma and, hence, the taste of beer. A gas chromatographic system has been developed to assist in the objective characterization of hop aroma. The first component of this system is an equilibrium headspace sampler with an integral adsorbent trap. A hop or beer sample is placed in a sealed vial and maintained at an elevated temperature for a fixed period of time. During this time, VOCs from the sample migrate into the vapor (headspace) phase inside the vial. This vapor is then vented into an cooled adsorbent trap to focus and concentrate the VOCs. The VOCs in the trap are thermally desorbed and delivered to a gas chromatograph (GC) for component separation. The chromatographic column used for the separation is a 60 m × 0.32 mm × 0.5 µm Carbowax column (same stationary phase as used in ASBC Method Hops-17). The effluent from the chromatographic column is split between a mass spectrometer (MS) and an olfactory port (OP). The splitting device is fabricated using chemically deactivated laser-etched micro-channel wafer technology to ensure minimum dispersion and adsorption of compounds eluting from the GC column. The MS system enables the detection, identification, and quantification of each VOC component. The MS used in this work is a new single quadrupole designed specifically for GC use and has an enhanced sensitivity to enable spectral identification of hop VOCs at very low levels. The olfactory port is a new design that enables the operator to smell each component as it elutes from the GC column in relative comfort. In this way, the chemical profiles generated by the MS may be correlated against the subjective organoleptic information obtained from the olfactory port. This presentation will describe the design and application of this system. A wide variety of hop types have been examined using this system, including American West Coast strains, English strains, and noble strains. Both leaves and pellets have been examined. A variety of beers have also been examined. This system can be used for the quality control of hops prior to brewing and to troubleshoot beer after production.

Andrew Tipler is the chromatography R&D manager at PerkinElmer in Shelton, CT. He is English, obtained a degree in pure chemistry at the University of Manchester, and worked for many years in various laboratories in England. Since joining PerkinElmer at their English site in 1983, he has been involved in the development and application of nearly all the company’s GC products. He moved to the company’s site in the United States in 1993 and continued to work on new GC technology and applications. He has been granted a total of 25 patents and gives papers at many key GC conferences around the world. He is also a keen home brewer and has won awards in regional competitions, particularly for English bitters. He is studying to become a judge in the BJCP program.