Mechanical Characterization of Individual Brewing Yeast Cells Using Microelectromechanical Systems (MEMS): Cell Rupture Force and Stiffness

Abstract

The mechanical properties of individual yeast cells were measured using microelectromechanical systems (MEMS). Samples were taken throughout two controlled fermentations conducted as per ASBC Yeast-14: one utilized ale yeast (Saccharomyces cerevisiae, “red ale”) and the other utilized a lager strain (S. pastorianus, “SMA”). At least five lager and five ale cells were tested at each fermentation phase (start, middle, and end). Cell compression was induced by a MEMS squeezer, and displacement measurements were taken using optical microphotographs. The failure of each cell was similar; the cell would undergo minor deformation until visible rupture occurred, followed by significant cell shrinkage. Across all fermentation phases ale cells ruptured under an average force of 0.28 ± 0.05 μN, whereas lager cells ruptured at 0.47 ± 0.10 μN. The average stiffness at the midpoint of fermentation was found to be 4.8 ± 1.0 and 5.3 ± 0.9 μN/μm for ale and lager cells, respectively. The use of MEMS technology to study physical characteristics of brewing yeast during fermentation has not previously been attempted (to the authors' knowledge). This study may assist brewers in the selection of process parameters to improve yeast health and in the design of novel yeast handling technologies.

• Brewing yeast cells
• Lager
• Ale
• Microelectromechanical systems (MEMS)
• Rupture force
• Stiffness
• Fermentation
• Cell wall