Malt and Grains Session
Philip Wietstock, Technische Universität Berlin, Germany
Co-author(s): Christian Mueller, Technical University, Berlin,
Germany; Maik Kleinwaechter and Dirk Selmar, Technical University,
Braunschweig, Germany; Frank-Jürgen Methner, Technical University,
Berlin, Germany
ABSTRACT: Nowadays, very large malt batches are processed,
which frequently leads to heterogeneities within the grain beds. As a
result beta-glucanase activities, among others, vary within the batches,
thus high beta-glucan concentrations remain unhydrolyzed in parts of
the batches and can lead to lautering and filtration problems during the
brewing process. The kernels’ enzyme activities mainly depend on their
physiological status. Accordingly, the metabolic status of the seeds
corresponds to a reliable marker for detecting heterogeneities in the
grain beds and for predicting potential processing problems. Up to now,
the Calcofluor method according to Carlsberg has been the only
standardized method to determine the kernels’ homogeneity; however, its
results are not very precise. In this study, malting trials under
differing conditions were carried out to assess if gamma-aminobutyric
acid (GABA) can be used as a reliable marker for determining the
physiological status of the kernels. Malting trials from different
barley varieties were conducted under differing conditions (steeping
degree, steeping, germination temperature, and anoxia) and using
different scales (pilot and industrial trials). The malts produced were
evaluated by standard malt analyses. Additionally, the content of GABA
was analyzed in samples taken during malting using HPLC and compared
with germination control parameters (chitted kernels, acrospire length).
The study demonstrates that the accumulation of GABA in malt kernels is
influenced by many factors such as anoxia and long wet periods;
however, relevant parameters such as higher steeping degree and raised
temperatures during steeping and germination were shown to increase GABA
formation to a higher extend. Further outcomes of this study suggest
that short periods of anoxia during malting do not harm the kernel’s
physiological status; the kernels survived, and germination resumed. The
heterogeneities in large malting batches were examined in trials using
an industrial malting plant. Varying temperatures and O2/CO2
ratios could be detected in the high grain beds of three different
steeping systems. Without aeration of the grain, oxygen consumption was
very fast, especially in the later steeping phases (dry and wet). Anoxia
again did not lead to a dying of the kernels but to a delayed growth of
rootlets and acrospires. Nevertheless, the formation of the most
important enzymes alpha- and beta-amylase and beta-glucanase was slower
at the beginning of the germination, but no markable lack of enzymatic
activities could be found at the end of germination. During kilning the
formed GABA was decomposed faster in the lower layers of the grain bed.
The outcome of this research provides the brewing and malting industry
with new results concerning the use of the stress metabolite GABA as an
indicator for evaluating the physiological status of germinating barley.
Philip
Wietstock is a scientific assistant at the Technische Universität
Berlin, Germany. After graduating from his biotechnology studies with a
diploma in engineering from the Technische Universität Berlin (2009), he
worked for one year as an intern at the Department of Food Science and
Technology at Oregon State University, Corvallis, OR. In 2011, he
transferred to his present position, where he is working on his
dissertation which focuses on the investigation of the influence of hops
on oxidative beer stability.
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