Fusarium infection in malting barley drives trichothecene transfer and transformation during brewing process, impacting beer safety and composition.

Fusarium contamination in malting barley poses a constant threat of mycotoxin exposure in brewing. However, the chemical transformations of trichothecenes toxins during processing and the broader impact of fungal contamination on beer quality are insufficiently understood. In this study, we inoculated barley grains with Fusarium culmorum to track the behavior of deoxynivalenol (DON) and its conjugates, deoxynivalenol-3-glucoside (DON-3G) and 3-acetyldeoxynivalenol (3-AcDON), through a controlled malting and brewing sequence. Quantitative LC-MS/MS and qPCR analyses revealed extensive fungal activity and toxin formation in malt, reaching 1,054 µg kg⁻¹ DON and 4,352 µg kg⁻¹ DON-3G, respectively. Mashing and lautering facilitated the release of matrix-bound toxins, whereas fermentation represented the key stage for biochemical transformation. During this phase, yeast metabolism markedly increased free DON through the hydrolysis of DON-3G and deacetylation of 3-AcDON. During maturation, a partial re-glycosylation of DON was observed. Despite toxin conversions, the final Fusarium infected batch (FIB) still contained substantial residues of the original toxins load in malt: 99% of DON, 50% of DON-3G, and 84% of 3-AcDON. Fusarium likewise affected chemical and sensory quality of beer: beer from infected kernels showed darker color, elevated soluble nitrogen, and a higher Thiobarbituric Acid Index, pointing toward intensified Maillard reaction activity. Untargeted FT-ICR-MS and LC-ToF-MS analysis confirmed infection-driven shifts in the beer’s molecular composition, revealing elevated Maillard-derived compounds and a distinct biochemical imprint of infection marked by fungal metabolites such as hydroxytrichodiene and host-defense conjugates including cinnamoyl-serotonin derivatives. Our findings show that F. culmorum infection affects both consumer safety of beer and the fundamental (bio)chemistry underlying its composition.