A new method for estimating the premature yeast flocculation potential of malts using 180 mL scale fermentation

Yeast and Fermentation Session
Yasuhiro Muraoka, Frontier Laboratories of Value Creation, SAPPORO BREWERIES LTD., 10 Okatohme, Yaizu, Shizuoka, 425-0013 Japan
Co-author(s): Masahide Sato and Tatsuro Shigyo, Frontier Laboratories of Value Creation, Sapporo Breweries Ltd., Yaizu, Japan

ABSTRACT: Premature yeast flocculation (PYF) refers to the phenomenon whereby yeasts flocculate prematurely during fermentation in the presence of high sugar concentrations. PYF is considered to be induced by so-called premature yeast flocculation inducing factors in malts, although the structure and the mechanism of how they cause PYF is unclear. It is very important for brewers to detect malts that cause PYF because it leads to low attenuation and results in an undesirable flavor in beer. In order to estimate the potential of malts regarding PYF (PYF potential), several methods have been developed in the past. However, these methods are time-consuming; they take 2 days to 1 week to complete the fermentation tests. In this report, we developed a new method for evaluating the PYF potential more effectively using 180 mL scale fermentation. In our method, the floating cells were measured by counting yeast cell numbers or by measuring the optical density of suspensions during fermentation. We prepared wort from malts having or not having PYF potential, performed fermentation, and compared the degree of flocculation. As a result, we were able to evaluate the PYF potential only after 24 hr of fermentation, which remarkably shortened the assay period. We expect our method to be useful for predicting the PYF potential of malts and enabling us to prevent PYF in brewing and to improve beer quality.

Yasuhiro Muraoka received an M.S. degree in biological sciences from the Nara Institute of Sciences and Technology. He joined the Hokkaido brewery of Sapporo Breweries Ltd. in 2005 as a brewing engineer. Since 2010, he has been working in Frontier Laboratories of Value Creation as a research brewer.