Quantifying the impact of beer unit operations (mashing, fermentation, and maturation) on Bacillus thuringiensis behavior

Abstract

This study investigates the germination and survival of Bacillus thuringiensis strains during different stages of the brewing process, considering the impact of pH, hop concentration, and physicochemical parameters. Three B. thuringiensis strains carrying hop resistance genes (horA, horC, or both) were evaluated in Pilsner-style beer during mashing, fermentation, and maturation. Results showed that mashing was the most critical stage, with bacterial counts decreasing by over 5 log₁₀ CFU/mL within 6–9 min, while fermentation and maturation allowed spore survival. Additionally, at pH 5.7, B. thuringiensis strain C:118 exhibited significant growth (p < 0.05), whereas strains C:002 and C:206 remained stable. Hop type and concentration influenced bacterial inhibition, with boiling enhancing antimicrobial activity, suggesting the release of bioactive compounds. However, some hop varieties lacked inhibitory effects against B. thuringiensis, highlighting the need for quality control measures beyond sensory attributes like bitterness. These findings confirm that spore-forming bacteria can persist throughout brewing and, depending on the final product composition, may germinate and proliferate under favorable conditions.