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Doctoral dissertation: Microbes in the tailoring of barley malt properties
27.08.2007
Research Scientist Arja Laitila has investigated the impacts of bacterial and fungal communities on barley germination and on malt properties in her PhD thesis work. She will defend her thesis "Microbes in the tailoring of barley malt properties” at the University of Helsinki on 31 August 2007.
Microbes – bacteria, yeasts and filamentous fungi - have a decisive role in
the barley-malt-beer chain. Microbes greatly influence the malting and brewing
performance as well as the quality of malt and beer. A major goal of the
dissertation was to study the relationships between microbial communities and
germinating grains during malting.
Laitila’s research
revealed that by modifying the microbial populations during malting, the
brewing efficiency of malt can be notably improved. Well-characterized lactic
acid bacteria and yeasts provide a natural way for achieving safe and balanced
microbial communities in the malting ecosystem. She showed that the malting
ecosystem is a dynamic process, exhibiting continuous change. The microbial
communities consisting of various types of bacteria, yeasts and filamentous
fungi form complex biofilms in barley tissues and are well-protected.
Inhibition of one microbial population within the complex ecosystem leads to
an increase of non-suppressed populations, which must be taken into account
because a shift in microbial community dynamics may be undesirable. Laitila
found some new microbial species in the malting ecosystem.
Suppression
of Gram-negative bacteria during steeping proved to be advantageous for grain
germination and malt brewhouse performance. Fungal communities including both
filamentous fungi and yeasts significantly contribute to the production of
microbial b-glucanases and xylanases, and are also involved in proteolysis.
Well-characterized lactic acid bacteria (Lactobacillus plantarum VTT E-78076
and Pediococcus pentosaceus VTT E-90390) proved to be effective way in
balancing the microbial communities in malting. Furthermore, they have
positive effects on malt characteristics and they improve wort separation.
Previously
the significance of yeasts in the malting ecosystem has been largely
underestimated. This study showed that yeast community is an important part of
the industrial malting ecosystem. Yeasts produced extracellular hydrolytic
enzymes with a potentially positive contribution to malt processability.
Furthermore, several yeasts showed strong antagonistic activity against field
and storage moulds. Addition of a selected yeast culture (Pichia anomala VTT
C-04565) into steeping restricted Fusarium growth and hydrophobin production
and thus prevented beer gushing. Addition of Pichia anomala into steeping
water tended to retard wort filtration, but the filtration was improved when
the yeast culture was combined with Lactobacillus plantarum E76. The
combination of different microbial cultures offers a possibility to use
different properties, thus making the system more robust.
According
to Arja Laitila new improved understanding of complex microbial communities
and their role in malting enables a more controlled process management and the
production of high quality malt with tailored properties.
Dissertation:
Microbes
in the tailoring of barley malt properties
Microbial
ecosystem in malting under the spotlight:
FESEM micrograph of Lactobacillus plantarum (lactic acid bacteria) and Pichia
anomala (yeast) cells adhered to barley seed-coat tissues. Photo by: Mari
Raulio (University of Helsinki) and Arja Laitila (VTT).