The Dynamics of Indigenous Epiphytic Bacterial and Fungal Communities of Barley Grains Through the Commercial Malting Process

Microbial activity is present at every step of the malting and brewing process. It is, therefore, critical to managing the grain-associated microbial communities for the production of high-quality malts. Earlier studies and reviews have only focused on the most abundant or culturable microorganisms of the malting environment. Furthermore, fungal-bacterial interactions have not been studied through the barley malting process as had been done for other fermented foods such as cheese and wine. This study used a metabarcoding approach to characterize the barley and the malt-associated epiphytic fungal and bacterial communities and provided the most comprehensive analysis to date of the dynamic shift in diversity, compositional structure, and potential functional roles of the grain-associated microbiome through the commercial malting process. We revealed microbial taxa that have not been identified before in a malting environment and identified functional guilds generating organic acids or degrading the endosperm cell walls and storage proteins that may affect malting efficiency and consistency. Ecological network reconstruction suggested that malting destabilized grain epiphytic microbiome which could be vulnerable to less optimal environmental conditions. This study expanded our knowledge in microbial quality and safety of malt and could help manage microbial-associated problems in the commercial malting industry.