Measuring Lager and Ale Yeast Viability and Vitality Using Fluorescence-Based Image Cytometry

Leo Li-Ying Chan, Dan Driscoll, Dmitry Kuksin, and Stephanie Saldi. Nexcelom Bioscience LLC, Lawrence, MA, U.S.A.
Saccharomyces cerevisiae has been indispensable to the production of beer for generations. Throughout the brewing process, establishing proper yeast viability and vitality is a crucial concern for proper cell growth, optimal yield, and flavor consistency. Viable yeast are those with intact membranes, whereas vital yeast are those cells with quantifiable metabolic activity and the capacity to proliferate. It is possible to have yeast that are viable but not actively propagating, and this adversely affects the fermentation process. As a rule, evaluating yeast viability involves methylene blue staining followed by manual counting with a hemacytometer. This method is time consuming and introduces human error. Here, we detail the utility of Cellometer Vision image cytometry for multichannel fluorescent assessment of yeast viability and vitality. Using nine fluorescent stains, such as nucleic acid stains (propidium iodide [PI], ethidium bromide, 4ʹ,6-diamidino-2-phenylindole, and 7-aminoactinomycin D), membrane potential, intracellular, and enzymatic dyes (oxonol, 1-anilino-8-naphthalene sulfonic acid, and carboxyfluorescein diacetate, acetoxymethyl ester [CFDA-AM]), and dual fluorescent stain combinations (acridine orange/PI and CFDA-AM/PI), we validated each against the traditional methylene blue method. Finally, Avery Brewing Company carried out a time-course analysis to compare the viability and vitality of lager and ale yeast to obtain a better understanding of the physiological and metabolic characteristics of yeast cells during the fermentation process. This information provided diagnostic criteria for monitoring the robustness of yeast in a way that may improve quality control procedures and yield beverage products that are more consistent in quality, flavor, and alcohol content.

Keywords: Image cytometry, Yeast viability, Yeast vitality, Methylene blue, Hemacytometer