Microbes in the tailoring of barley malt properties: Dissertation

Malted barley (malt) is traditionally used in the production of beer and distilled spirits. In addition, it can be processed into ingredients for different areas of the food industry. Malting, the controlled germination of cereal grains, is a complex biological process involving a wide range of biochemical and physiological reactions. The diverse microbial communities naturally colonizing barley grains play a crucial role in this process. Therefore, the malting process can be considered as an ecosystem involving two metabolically active groups: the germinating grains and the diverse microbiota. It is evident that the multitude of microbes greatly influences the malting process as well as the quality of the final product. The main goal of this thesis was to study the relationships between microbes and the germinating grain during the malting process. Furthemore, this study provides a basis for tailoring of malt properties with natural, malt-derived microbes. The results of this study showed that the malting ecosystem is indeed a dynamic process and exhibits continuous change. Microbes embedded in biofilms within the husk tissues were well protected. Reduction of one population within the complex ecosystem led to an increase in competing microbes. This should be taken into account when changes are made in the malting process. Using different molecular approaches we also found that the diversity of microbes in malting was much greater than previously anticipated. Some potentially novel bacterial and fungal species were found in the malting ecosystem. The microbial communities greatly influenced grain germination and malt properties. By suppressing Gram-negative bacteria during steeping, barley vitality and malt brewhouse performance were improved even in the case of good-quality malting barley. The fungal community consisting of both yeasts and filamentous fungi significantly contributed to the production of microbial glucanases and xylanases, and was also involved in the proteolysis. Previously the significance of yeasts in the malting ecosystem has been largely underestimated. This study showed that a numerous and diverse yeast community consisting of both ascomycetous (25) and basidiomycetous (18) species occured in the industrial malting ecosystem. Yeast and yeast-like fungi produced extracellular hydrolytic enzymes with a potentially positive contribution to malt processability. Furthermore, several yeast strains showed strong antagonistic activity against field and storage moulds. The management of microbes in the whole barley-malt-beer chain is extremely important with respect to both process and product safety and quality. Lactic acid bacteria (LAB) can be used to tailor the malt properties. Lactobacillus plantarum VTT E-78076 (E76) and Pediococcus pentosaceus VTT E-90390 (E390) added to steeping water promoted yeast growth and restricted the growth of Gram-negative bacteria and Fusarium fungi. Furthermore, they had positive effects on malt characteristics and notably improved wort separation. Some of the beneficial effects observed with LAB were due to the lactic acid production and concomitant lowering of pH. Futhermore, increase in the number of yeasts could partly explain the enhanced xylanase and -glucanase levels observed after LAB addition. Addition of a specific yeast culture (Pichia anomala VTT C-04565) into the steeping water of barley restricted Fusarium growth and hydrophobin production during malting and thus prevented beer gushing. This study also revealed that P. anomala retarded the wort filtration, but that the filtration performance was recovered when yeast cultures were combined with L. plantarum E76. The combination of different microbial cultures offers a possibility to utilise their different properties, thus making the system more robust. Improved understanding of the complex microbial communities in the malting ecosystem will enable more efficient control of unwanted microbiological phenomena as well as utilization of the beneficial properties of microbes in malt production.