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The impact of long-term pitching yeast storage on viability and fermentation performance - WINNER OF LUDWIG-NARZISS-AWARD 2023
C. Zufall, L. De Oliveira, I. Mendoza and C. de Lima

The purpose of this study was to evaluate which yeast storage conditions allow the pitching yeast to conserve maximum viability and fermentation performance. For that, a lager yeast cropped after a third fermentation cycle was subjected to different pretreatment and storage conditions during a three-month period. Pretreatment included washing the yeast with sterile process water. Storage conditions were varied by different gassing regimes with either air or carbon dioxide. Alternatives for an activation protocol prior to fermentation were also evaluated at laboratory scale after storage. Yeast was tested weekly for viability and microbiological purity. Additionally, a laboratory scale fermentation was performed monthly to evaluate the performance of the yeast from the different trials. Finally, the combination of the most promising pretreatment, storage conditions and re-activation technique was successfully tested on industrial scale. The availability of a large amount of pitching yeast complying with the required viability, fermentation performance and microbiological purity is a decisive advantage during the time-critical run-up procedure after a brewery shutdown. This may save the brewery several weeks before beer sales can resume.

Descriptors: pitching yeast, long-term storage, viability