Ultrasound assisted thermal pasteurization of beers with different alcohol levels: Inactivation of Saccharomyces cerevisiae ascospores

The industrial production of beer ends with a process of pasteurization. This study investigated the ultrasound assisted thermal pasteurization of beer or thermosonication (TS), aiming the inactivation of Saccharomyces cerevisiae ascospores, the most resistant form of the yeast. The efficacy of 30 s TS in batch and continuous operation mode at 60, 65, and 70 °C was studied. After that the ascospore inactivation in beers was modelled and TS pasteurization conditions recommended. Lastly, the inactivation of S. cerevisiae ascospores in beer by TS vs. thermal processing at 55 °C was compared. Ultrasound alone and continuous TS operation were not enough to achieve the minimum beer pasteurization requirement aiming at S. cerevisiae spore inactivation. The TS survival curves were fitted with a Weibull model. TS at 50 °C-1.9 min and TS at 55 °C-26 s were enough for pasteurization, as opposed to 55°C-38 min thermal process. The results are helpful for designing appropriate thermosonication conditions to pasteurize beer with different alcohol contents and other beverages.