Assessment of yeast physiology during industrial-scale brewing practices using the redox-sensitive dye resazurin

Beer refermentation in bottles is an industrial process utilized by breweries where yeast and fermentable extract are added to green beer. The beer is refermented for a minimum of 2 weeks before distribution, with the physiological state of the yeast a critical factor for successful refermentation. Ideally, fresh yeast that is propagated from a dedicated propagation plant should be used for refermentation in bottles. Here, we explored the applicability of the fluorescent and redox-sensitive dye, resazurin, to assess cellular metabolism in yeast and its ability to differentiate between growth stages. We applied this assay, with other markers of yeast physiology, to evaluate yeast quality during a full-scale industrial propagation. Resazurin allowed the discrimination between the different growth phases in yeast and afforded a more in-depth understanding of yeast metabolism during propagation. This assay can be used to optimize the yeast propagation process and cropping time to improve beer quality.