Rehydration of active dry brewing yeast and its effect on cell viability

The use of active dry yeast (ADY) in the brewing industry is becoming increasingly attractive due to several key features, including its capacity to be stored conveniently and to be prepared rapidly for use. However, some studies have reported that undesirable effects may occur when employing lager strains in the ADY form, such as abnormal flocculation, haze formation and a less stable foam structure. These effects have been linked to reduced viability, caused by cell death during the drying and rehydration processes. It is known that the means by which yeast is rehydrated is important to maintain membrane integrity and to prevent potentially lethal damage from occurring. In order to determine the impact of rehydration conditions on yeast viability, three industrially manufactured ADY strains were examined. Each strain was rehydrated using a variety of parameters and monitored for cell viability using slide culture and a variety of brightfield and fluorescent stains.