Beer fermentation relies on yeast cells remaining suspended as they convert sugars into ethanol and flavor compounds. However, in Premature yeast flocculation (PYF), yeast aggregates and settles prematurely, interrupting fermentation and causing production losses. PYF has been linked to microbial contamination, cell wall composition, malt properties, and fermentation conditions, but the precise biochemical triggers remain unclear. Previous studies have predominantly investigated genetic and protein-level effects but have not fully explained the metabolic signals driving flocculation. Given the complexity of yeast adhesion mechanisms and the influence of cellular metabolites on cell-surface interactions, identifying metabolite-level regulators may be essential to resolving PYF. Due to these challenges, a deeper metabolic investigation is needed to clarify the causes of PYF.
Researchers from Tsingtao Brewery and Zhejiang University conducted a metabolomics-based study to explore biochemical drivers underlying PYF. The findings were published (DOI: 10.1093/fqsafe/fyaf041) on August 28, 2025, in Food Quality and Safety. By analyzing malt wort and fermentation samples with varying PYF severity and validating metabolite effects through controlled yeast fermentation assays, the team identified galangin as a key promoter of yeast aggregation. The study provides the first metabolomics evidence connecting a specific plant-derived metabolite to PYF.
The researchers performed UPLC-MS/MS metabolite profiling across barley malt wort and fermentation broths exhibiting different degrees of PYF. A total of 256 metabolites were detected, including amino acids, sugars, phenols, lipids, and flavonoids. Statistical comparison identified 46 differential metabolites in fermentation broth and 30 in wort, with 13 metabolites shared across conditions. Among them, the flavonoids galangin and daidzein showed a strong positive correlation with fermentation duration in high-PYF samples.
To determine whether these metabolites directly affect yeast behavior, the team conducted reverse addition experiments. Galangin was added to yeast cultures at controlled concentration and resulted in rapid yeast sedimentation, visibly clearing the wort and significantly decreasing OD600 values—indicating enhanced flocculation activity. Conversely, daidzein increased turbidity, suggesting it may interfere with flocculation via solubility-related mechanisms rather than direct interaction.
The demonstration that galangin actively promotes yeast aggregation provides direct biochemical evidence linking a natural malt-derived metabolite to premature flocculation. The results highlight the role of small molecular compounds—not just proteins or polysaccharides—in shaping fermentation performance.
"Our findings shed new light on the biochemical triggers that can disrupt beer fermentation," said the study's corresponding authors. "Identifying galangin as a positive regulator of yeast flocculation provides a fresh perspective beyond classical genetic or microbial contamination explanations. This work opens the door to developing diagnostic screening tools for malt and optimizing fermentation practices to prevent PYF, ultimately improving product consistency and production efficiency."
This research provides new strategies for the brewing industry to monitor and control PYF. Since galangin originates from barley malt, its abundance may be influenced by raw material selection, malting conditions, and storage environment. Brewers may benefit from metabolic screening of malt batches, development of predictive fermentation quality indicators, or process adjustments to reduce galangin accumulation. Further studies could explore molecular interaction mechanisms between galangin and yeast cell surfaces to enable targeted interventions. Overall, the discovery offers practical solutions to enhance fermentation stability, beverage quality, and economic yield.
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References
DOI
10.1093/fqsafe/fyaf041
Original Source URL
https://doi.org/10.1093/fqsafe/fyaf041
Funding information
This work was supported by the National Natural Science Foundation of China (No. 32171917), the Open Research Fund of the State Key Laboratory of Biological Fermentation Engineering of Beer (No. K202104), and the Key Research of Zhejiang Province of China (No. 2021C02064-3).
About Food Quality and Safety
Food Quality and Safety (FQS) is an open access, international, peer-reviewed journal providing a platform to highlight emerging and innovative science and technology in the agro-food field, publishing up-to-date research in the areas of food quality, food safety, food nutrition and human health. It is covered by SCI-E and the 2024 Impact Factor (IF)=4.4, 5-yr IF=4.8.