History of Yeast Flocculationbwith an Emphasis on Measurement Techniques

Authors: MEHTA, DEVANSHU - University Of Florida; CURTIS, SAVANNA - University Of Florida; Rudolph, Arthur; ST MARY, COLETTE - University Of Florida; GOODRICH, RENEE - University Of Florida; SCHNEIDER, KEITH - University Of Florida; MACINTOSH, ANDREW - University Of Florida

Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2020
Publication Date: 9/4/2020
Citation: Mehta, D.V., Curtis, S.J., Rudolph, A.B., St Mary, C., Goodrich, R., Schneider, K.R., Macintosh, A.J. 2020. History of Yeast Flocculationbwith an Emphasis on Measurement Techniques. Journal of the American Society of Brewing Chemists. https://doi.org/10.1080/03610470.2020.1806006.
DOI: https://doi.org/10.1080/03610470.2020.1806006

Interpretive Summary: In many types of yeast, cell surfaces play an important role in mediating the interactions between the yeast, other organisms, and the environment. A well-studied example of this is flocculation in brewer’s yeast, which is a natural phenomenon wherein thousands of yeast cells clump together and fall out of solution at the end of the fermentation process. Yeast flocculation is often relied upon by brewers as a natural means of filtration as clumps of yeast cells (flocs) typically settle to the bottom of the fermentation vessel. However, these flocs have been linked to premature ending or “hung” fermentations – a problem that has long baffled brewing scientists. Since the early 1900s researchers have explored numerous methods to identify the flocculation characteristics of yeast. Traditional methods have contributed to an understanding of the fundamentals of flocculation by assessing the impact of stressors such as pH, temperature, wort density, and ethanol content on the flocculence of yeast. A better understanding of how yeast cells function in yeast living in high sugar concentration environments during brewing will assist in our understanding of how yeasts interact in similar sugar concentrations of floral nectar, as well as resultant influence that nectar microbes have on attracting or repelling pollinators, and the subsequent dispersal of these microbes.

Technical Abstract: Flocculation of yeast is a natural phenomenon wherein cells clump together and come out of suspension. This is often relied upon by brewers as a natural means of removing yeast, as clumps of yeast cells (flocs) typically precipitate from the fermentation vessel. A problem that has long frustrated brewers is when yeast flocculation does not proceed as expected. This has been linked to a fermentation’s premature ending (“hung” fermentation). Since the early 1900s, researchers have explored numerous methods to identify the flocculation characteristics of yeast. Traditional methods have contributed to an understanding of the fundamentals of flocculation by assessing the impact of stressors (e.g., pH, temperature, wort density and composition, and ethanol content) on the flocculence of yeast. In 1994, conventional measurement techniques were combined with modern technology to develop the American Society of Brewing Chemist’s method “Yeast 11,” which was revised by the society in 2011. This method succeeded in the identification and definition of the flocculence characteristics of particular yeast strains but has not taken into account the changes in flocculation tendency over time for later generations of the same yeast strain. The ASBC also describes a fermentation assay to assess aberrant yeast behavior such as premature yeast flocculation (PYF) in the “Yeast 14” method. The current challenge in flocculation research is understanding the changing genetics of flocculation throughout the usage of a yeast strain in a fermentation process. This review details the evolution of yeast flocculation measurement, our current understanding, and potential future developments.