P-06 - Evaluating the Impact of Surface Microbiomes from Germinating Barley on the Flavor Profile of Malted Rice

Beer is traditionally brewed using malted barley, but its gluten content poses challenges for individuals with celiac disease. As a result, there is growing interest in replacing barley with rice, a gluten-free and widely available cereal. Additionally, the increasing cost of barley and its limited cultivation in certain regions have positioned rice as a viable alternative for brewing.  While rice meets several malt quality requirements, rice-based beers often lack the rich, complex flavor profile flavor profile that characterizes barley malt. Historically, beer flavor has been attributed to barley genotype, Maillard reaction products formed during malt kilning, and malt-hop interactions. However, recent research suggests that the microbial community during the malting process plays a significant role in shaping malt flavor. While microbial contributions to fermentation are well established, their impact on flavor development during malting remains underexplored. Over time, each malting plant develops a distinct, stable microbial community due to repeated malting cycles and environmental conditions. These in-house microbiomes can influence malt quality, enzyme activity, and flavor formation. This study investigates whether microbial communities from germinating barley sourced from different germination beds and malt houses can be leveraged to develop rice malt with a flavor profile comparable to barley malt. To explore this, we collected barley samples from multiple germination beds across two commercial malt houses. Within each bed, samples were systematically taken from various depths and pooled to create a representative microbiome sample. These pooled samples were then subjected to microbial isolation. The resulting microbial suspensions were then applied to rice grains undergoing malting in our optimized benchtop malting system for rice, specifically during the third wet stage of steeping, when seeds become friable. After kilning, hydrolytic enzyme activity and volatile aroma compounds of the malted rice were analyzed qualitatively and quantitatively using gas chromatography-mass spectrometry (GC-MS/MS) solid phase microextraction (SPME) technique. The results were compared to both control rice and barely malt (produced without microbial inoculation) samples. Additionally, raw barley and rice seeds were analyzed to account for inherent differences before malting. The findings from this study are expected to provide insights into the influence of the barley microbiome on the overall aroma of rice malt, potentially enabling establishing a microbial-assisted malting strategy to enhance the flavor complexity of gluten-free rice malt, providing a sustainable and cost-effective alternative for brewing high-quality rice-based beer.