Doctoral dissertation: Microbes in the tailoring of barley malt properties
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).