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2017 Master Brewers Conference
96. Optimization of premature yeast flocculation (PYF) factor assay

Jigar Brown, Rahr Malting Co., Shakopee, MN, U.S.A.

Coauthor(s): Patricia Aron, Rahr Malting Co., Shakopee, MN, U.S.A.; Xiang Yin, Rahr Malting Co., Shakopee, MN, U.S.A.; Paul Kramer, Rahr Malting Co., Shakopee, MN, U.S.A.

Yeast, Fermentation, and Microbiology

Premature yeast flocculation (PYF) is an issue of concern for brewers. PYF negatively impacts fermentation; PYF leads to residual fermentable sugars, lower final alcohol content, and also causes filtration issues. Research regarding the variables that cause PYF is necessary: malt processing, malt quality, yeast genetic variation, and wort/beer environmental fermentation factors. A quick and reliable method to detect PYF potential would be highly beneficial. This study compared two methods that evaluate PYF potential and applied modifications to yeast preparation. The two methods tested include the EBC 2.0 liter fermentation tube method and the Jibiki, Sasaki, Kagami, and Kawatsura, 2006 method. The former is a seven-day fermentation method done in EBC tubes at 9 °C, while the latter is a two-day fermentation done in 50 mL graduated cylinders at 25 °C. SMA yeast was used for all tests done in this study due to its sensitivity to prematurely flock. The Jibiki et al. test method is shorter; however, the yeast propagation method is more tedious and time consuming than the EBC method. The propagation method for the EBC tube method involves propagating yeast in 400 mL of YPDW at room temperature while stirring in an orbital shaker. The Jibiki et al. method requires a two-stage yeast propagation method in which the yeast propagates in 10 mL of YPM for 3–4 days without agitation and is then pitched into 250 mL of YPM6 and allowed to propagate for 30 more hours at 25 °C while rotating at 160 rpm. Differences in the methods also include yeast pitching temperatures (room temperature for EBC and 4 °C for Jibiki et al.). The authors investigated modifications to yeast propagation in combination with both fermentation methods. Results indicate that yeast preparation and propagation technique impacts PYF performance. However with modification, a streamlined yeast propagation method combined with a shorter fermentation method led to the formulation of an optimized and more efficient method that yields consistent results.

Jigar Brown currently works at Rahr Malting Co. located in Shakopee, Minnesota, in the R&D Brewing Materials Lab as a brewing, research, and innovation scientist. He obtained a biology degree from the University of Minnesota in 2013. His interests include absorbing information on the technical aspects of brewing, gaining experience in the sensory department, and maintaining his role as an electronics/technology guru.

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