Growth Characteristics of Bacillus cereus in Sake and during Its Manufacture

Sake (Japanese rice wine) has been recognized as being low risk in terms of its microbiological safety. However, a confirmation of the food safety aspects of sake based on scientific evidence is important for establishing consumer confidence, in part because consumer concerns regarding food safety have increased. The presence of Bacillus cereus spores in refined rice wine has been reported, and in light of consumers' growing concern over food safety, the establishment of food and beverage safety is important for consumers' reassurance. Herein, to confirm the microbiological safety of sake, we investigated the content and growth of B. cereus. We conducted a spore addition test to determine whether B. cereus spores grow during sake production, and we observed no growth or germination of B. cereus spores during the manufacturing process. We also observed that processes such as solid-liquid separation and filtration help remove the risk posed by B. cereus. We then conducted a survey to assess the density of B. cereus in various commercial sake products. We analyzed 162 samples of commercial sake and observed that 11 of the products had >1 CFU of living cells in 1 mL of sake (detection rate, 6.8%). There was no product in which >= 100 CFU of living cells per 1 mL of sake was detected. Our findings confirmed that the density of these bacteria in sake is lower than that in other foods and that the probability of infection is very low. The emetic toxin produced by B. cereus was not detected in any of the sake samples. This is the first study based on experimental data demonstrating that B. cereus is not able to grow in sake or during the sake manufacturing process. We, thus, conclude that the safety risk of B. cereus in sake is negligible. Our findings indicating that B. cereus is not a significant hazard in the sake brewing process will contribute to food hygiene management based on scientific evidence in sake breweries.