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.
