University of Tasmania, Australia

The contribution of microbes during malting to the resultant quality of barley malt

The barley grain carries with it a community of micro-organisms referred to as its microbiota which consists principally of bacteria, including members of the Eubacteria and filamentous actinomycetes, filamentous fungi and yeasts. The degree to which the grain in colonised or contaminated depends on the field conditions under which the barley is grown and stored post harvest. Recently, Mandeep Kaur completed a landmark study using the molecular fingerprinting procedure TRFLP to show that there is substantial variability between the microbial populations of malt and barley sourced within Australia and internationally. Previous studies have shown that microbes may be responsible for improved barley germination during malting due to the secretion of plant hormones including gibberellin and auxin. Other studies have shown the various microbial species may lead to the secretion of enzymes such as b-glucanases, xylanases and proteases – enzymes that have a critical role in converting the barley endosperm into a form that is suitable for brewing during malting. For instance the b-glucanases and xylanases reduce wort and beer viscosity to benefit the efficiency of lautering and filtration stages in the brewing process. Proteases play a key role in hydrolysing barley storage proteins into amino acids and produce a range of peptides that are desirable (ie foam) or undesirable (ie haze) for beer quality. Overall, maltsters seek the optimisation of the modification of the barleys protein reserves during malting.