Rehydration of active dried yeast: impact on strength and stiffness of yeast cells measured using microelectromechanical systems: Rehydration of active dried yeast: impact on strength and stiffness of yeast cells measured using MEMS

This study investigated the rehydration of active dried yeast and the impact of temperature and wort density on the strength and stiffness of individual cells using a microelectromechanical system. Dried yeast was rehydrated using a variety of methods, including direct pitching into wort (13.6 degrees P) at 12, 22 and 30 degrees C, as well as propagation using YEPD media (4.2 degrees P). Cell viability was found to broadly correlate with measurement of cell strength and stiffness. Both wort density and temperature affected viability and physical characteristics of the cells after 1 h of rehydration. Yeast cells rehydrated at low temperature and high wort density burst at a lower force (0.26 +/- 0.02 mu N) than cells rehydrated using high temperature and low density media (0.50 +/- 0.10 mu N). Cells rehydrated at higher temperatures or using low density media showed no significant difference in strength and stiffness when compared with high viability, actively fermenting yeast. Changes in yeast physiology, owing to stress responses, may contribute to the observed differences in mechanical properties. These findings have application in brewery design, as pumping, centrifugation, storage and associated shear impart mechanical stress upon yeast cells. (C) 2018 The Institute of Brewing & Distilling