Investigating Malt Inducing Premature Yeast Flocculation: Threshold and Stability

Abstract

Premature yeast flocculation (PYF) has proven to be troublesome for the malting and brewing industries. It causes production difficulties and quality issues characterized by poor attenuation and low yeast cell counts post-fermentation. These issues result 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 industries rely on a variety of fermentation assays to indicate if a sample has PYF potential. This study used a modified miniature fermentation assay to determine if malt displays PYF potential and its associated threshold. In addition to traditional wort preparation methods, a wash technique was used to extract the PYF factor for use with synthetic wort. This modification to the assay eliminated the need for a controlled mashing device and reduced the amount of fine adjustments of the wort pre-fermentation to reach target start values. Control malt known to display no PYF attributes and PYF inducing malts were used in the study. To further our understanding of the PYF factor the “PYF Solution” extracted using the wash technique was subjected to various conditions pre-fermentation. The PYF Solution was mixed with the synthetic wort with varying ratios from 0-100% of the PYF solution (mixed with distilled water) to find the threshold at which PYF characteristics was displayed. The wort was treated with a combination of pre-fermentation boiling (60, 90, 120 minutes), chilling at 5°C and Freezing at - 30°C to further our understanding of the how these conditions affect the PYF factor. The trials were conducted using a 15 mL fermentation with a consistent temperature and pitch rate (21°C, 1.5 × 107 cells/mL). The change in absorbance and Plato was monitored throughout the fermentations. The control malt had no significant (P>0.05) difference in absorbance and Plato measurements from PYF inducing malt when the synthetic wort had <70% PYF solution. Synthetic wort containing >70% PYF solution had significant (P<0.05) differences from the control malt for both absorbance and Plato measurements. Boiling treatments alone did not produce significant (P>0.05) differences in the trials. Boiling followed by chilling yielded the same results and did not have significant changes (P>0.05) in fermentation characteristics. While most of the prefermentation treatments did not create differences in fermentation characteristics, boiling wort for >60 minutes and freezing before fermentation caused the >70% PYF solution to display the same fermentation characteristics as the control (P>0.05). These findings show that the PYF inducing factor may be susceptible to further processing. This thesis established two further findings. First, that the factor causing PYF must meet a threshold before it affects fermentation characteristics. Second, mashing the PYF-inducing grain may not be absolutely crucial for testing PYF potential of malt.