Beyond the Bubbles : a Study of Fungal Diversity and Gushing in Beer Production

Abstract: Gushing, violent and spontaneous over-foaming of beer, is a well-known quality reducing phenomenon encountered in the brewing industry. The present study investigated the impact of fungal contamination in barley grains, specifically focusing on gushing and the occurrence of pink kernels. A total of 101 seed samples of the malting barley cultivar Planet, harvested in 2020, were sourced from three seed handling sites in the southern and central parts of Sweden - Malmö, Lidköping, and Köping. The fungal communities within these samples were characterized using amplicon sequencing. Furthermore, machine learning techniques were employed to estimate the relative importance of these communities in inducing gushing and in forming pink kernels. Our findings reveal a diverse assembly of fungal species, including yeasts and filamentous fungi, across the analysed samples. The most common fungal genera were Fusarium, Cladosporium, Alternaria, Vishniacozyma, and Sporobolomyces. Particularly, a Fusarium species complex was identified as being associated with both the formation of pink kernels and the induction of gushing, emphasizing its implications to malting barley production. Additionally, this study also marks the first report of the fungal genera Vishniacozyma, and Itersonilia, in the context of pink kernels and malting barley research, highlighting their unexplored role in this context. The results point to the necessity for close monitoring of diseases in malting barley and the implementation of effective management strategies, such as improved crop rotations, in order to ensure that the quality and safety of malting barley meets industry requirements.