Identification, Traceability and Control of Butyric Acid Off-Flavor in Beer

Butyric acid contamination, typically characterized by distinct cheesy or sewage-like odor notes, is a common quality defect in beer. However, the flavor-active compounds causing this defect, their sources and dynamic changes, have not been fully elucidated. In this study, sensory evaluation, gas chromatography-mass spectrometry analysis, and high-throughput genomic sequencing were integrated to provide a comprehensive characterization of the compounds contributing to butyric acid off-flavor in beer and to identify their sources. The results revealed that butyric acid, isovaleric acid, and acetic acid were the primary flavor-active compounds. Clostridium and Bacillus were identified as the dominant bacterial genera, and notably, Clostridium_sensu_stricto was detected for the first time in wort filtration systems and syrup tank rinse water. The wort filtration system, syrup tank, and associated piping networks were determined to be critical control points for butyric acid contamination. Consequently, rigorous sanitation measures and enhanced microbial monitoring in these high-risk areas should be implemented. This study provides a robust theoretical foundation for tracing and preventing butyric acid contamination in the beer industry.