Optical Nanomotion Detection Reveals Nanomechanical Vitality of Brewer’s Yeast During Cold Storage

Yeast vitality during storage is essential for maintaining consistent fermentation per-formance. This study compares the physiological responses of top- and bottom-cropped Saccharomyces cerevisiae stored at 4°C for 20 days and evaluates Optical Nanomotion De-tection (ONMD) as a rapid, label-free vitality assessment tool. Classical assays (FUN-1, methylene blue, propidium iodide, glucose acidification power, glycogen content, and ethanol tolerance) were used to monitor metabolic activity, membrane integrity, and stress resilience. Bottom-cropped yeast retained metabolic activity, membrane stability, and energy reserves longer than top-cropped cells. ONMD revealed distinct single cell nanomotion signatures and detected mechanically active subpopulations even when traditional vitality indicators declined. Analysis of nanomotion slopes showed a pro-gressively steeper decline in top-cropped cells, indicating reduced temporal stability of nanomechanical activity during the 180-min recordings. Ethanol-challenge experiments confirmed the vitality dependence and stress-sensitivity of the ONMD signal. Together, these findings demonstrate that ONMD resolves cold-storage-induced changes in yeast nanomechanical vitality and provides complementary information beyond convention-al vitality and viability assays. ONMD offers a fast, reagent-free method for monitoring brewing yeast physiology and shows strong potential for integration into brewery quality-control workflows.