Threshold detection of premature yeast flocculation inducing malt using the miniature fermentation assay

Yeast and Fermentation Session
Joshua Adler, Dalhousie University, Nova Scotia, Canada
Co-author(s): Alex Speers, Dalhousie University, NS, Canada

ABSTRACT: Premature yeast flocculation (PYF) is a burden on the malting and brewing industries. It causes production difficulties and quality issues characterized by high sugar concentrations and low yeast cell counts post-fermentation. This results in variability in fermentation and flavor profiles. For this reason it is critical for brewers to assess their malts for PYF potential. To test for PYF potential in malt, the industry relies on a variety of fermentation assays. These methods can indicate if a sample displays PYF, but they do not determine the threshold at which PYF occurs. This study used modified miniature fermentations to investigate how a concentration of known PYF malt can influence the fermentation. Using wort prepared from varying ratios of control and PYF malts the change in absorbance and Plato was monitored. In addition, a PYF factor was extracted and used in varying amounts in a synthetic wort (i.e., malt extract) and fermented. While it is difficult to specify the actual amount of PYF factor extracted, this “PYF solution” was used in a second experiment to make up synthetic worts at levels of 0–100%. These trials were conducted using a 15 mL fermentation with a consistent temperature and pitch rate (21°C, 1.5 × 107 cells/mL). At designated intervals throughout each fermentation, yeast in suspension was monitored spectrophotometrically at 600 nm, and the apparent extract was measured. It was found that varying the ratio of either PYF malt or the amount of PYF factor could influence fermentation behavior. In the first experiment, low PYF malt levels (i.e., 20 and 40%) had no significant difference (P > 0.05) on absorbance. However, significantly different absorbance measurements (P < 0.05) were found when using concentrations of 60% PYF malt or higher. In the second series of experiments no difference from the control to the PYF solution at strengths of 20, 40, and 60% was observed (P > 0.05). But, significantly different fermentations (P < 0.05) were noted when malt extract was prepared with 80 and 100% PYF solutions. These findings agree with previous work but also suggest that PYF malt may be blended with typical malt as long as a critical threshold is not exceeded. This technique provides the brewer with another tool for making informed decisions when managing their process stream. Further statistical analysis of extracted measurements will also be presented.

Joshua Adler received a B.S. degree in biology from Dalhousie University in Halifax, NS, Canada. While pursuing his degree he became very interested in food science and was the first Dalhousie student to gain a minor in the discipline. His undergraduate thesis focused on problems encountered in wheat beer production ,which he presented at the 2011 ASBC Annual Meeting. Josh is continuing his brewing research as an M.S. candidate at “Dal” and hopes to contribute innovative findings on the fermentability of malt, as well as pass on valuable knowledge as a teaching assistant in product development and quality assurance courses. When outside the laboratory, Joshua can usually be found in the boxing ring training for an upcoming bout or enjoying a pint with his friends. One of his life’s ambitions is to visit as many of the worlds’ brewing and distilling regions as possible. He recently returned from the Lowland region of Scotland, where he visited a variety of breweries and distilleries.