EBC Symposium: Resources for the Future Session
Biendl Martin, Hopsteiner HHV m.b.H., Mainburg, Germany
Co-authors: Christina Schmidt and Andreas Stephan, Bitburger
Braugruppe GmbH, Bitburg, Germany; Christian Vogt and Thomas Hofmann,
Chair of Food Chemistry and Molecular Sensory Science, Technische
Universität München, Germany
ABSTRACT: Isomerization of alpha-acids from hops can result in different ratios of cis- to trans-iso-alpha-acids.
Whereas wort boiling in the brewhouse usually gives a ratio of approx.
2.5:1, it can be considerably higher in the case of isomerization
outside the brewery when using suitable catalysts. In contrast to
oxidative degradation processes, the conversion of iso-alpha-acids to
tri- and tetracyclic compounds during beer aging is only possible in the
trans form. Therefore it might be an advantage to use pre-isomerized hop products in order to maximize the cis
form in beer. For this study beers conventionally hopped with regular
pellets were compared to beers produced with isomerized pellets or
isomerized extracts respectively (dosages at the beginning of wort
boiling for each of the variations). In addition in-line
pre-isomerization (isomerization of conventional hop products in the
brewery prior to addition to the kettle) was investigated as another
alternative. All hop products used were from the same variety (Hallertau
Magnum, crop 2009). Their dosages were calculated in order to achieve
identical bitter units in the final beers (target: 30 IBU). All of the
four variations were produced in duplicate in a pilot brewery (20 hL
scale). Bottled beers were stored at 5 and 28°C. Analysis of fresh and
aged samples after 4, 8, and 12 months targeted bitter compounds (e.g., cis/trans-iso-alpha-acids,
allo-isohumulones, allo-isohumulonhydroperoxides,
allo-isohumulonhydroxides, tricyclohumols, tricyclohumenes, and
tetracyclohumols by means of HPLC-MS/MS) and volatile aroma compounds
(e.g., linalool and strecker aldehydes by means of GC-MS/MS). General
wort and beer parameter analysis showed no significant differences
between the various brews. Both the addition of regular pellets at the
beginning of wort boiling and their in-line pre-isomerization in the
brewery resulted in almost the same cis/trans ratio. As expected, beers produced with isomerized hop products showed higher ratios of cis- to trans-iso-alpha-acids,
and their concentrations of tricyclohumols, tricyclohumenes, and
tetracyclohumols were accordingly lower after aging. However, all of the
four types of beers hopped in different ways showed very similar
volatile aroma compound profiles, even during aging. Moreover sensory
evaluation of aged beers showed no preference for the variations higher
in cis/trans ratios of iso-alpha-acids.
Martin
Biendl received a Ph.D. degree in organic chemistry from Regensburg
University in 1990. He is head of the R&D/Analytical Department at
the German branch of the Hopsteiner Group, one of the largest
international hop growing, trading, and processing firms. His research
experience is in the field of hop-related needs for the brewing industry
and beyond. He is the representative of the International Hop Industry
Cooperation in the EBC Analysis Committee and, since 2001, chair of the
Hops Subcommittee. As an EBC representative he is also co-chair of the
International Hop Standards Committee.
