Assessing the effect of fungal infection of barley and malt on premature yeast flocculation

The phenomenon of premature yeast flocculation (PYF) is suspected to be caused (at least in part) due to fungal infection of barley. This study reports on an ongoing investigation that has identified a link between fungal pathogens and PYF behavior. Two varieties of barley, AC Metcalfe and CDC Bold, were exposed to each of three common barley fungal pathogens (Pyrenophora teres, Cochliobolus sativus, or Fusarium graminearum) and evaluated for PYF behavior during fermentation. Barley was infected in the field between flowering and grain maturation. Each sample was micro-malted, mashed, and fermented using a moderately flocculent yeast strain (SMA). Fermentations were performed using the ASBC "Miniature Fermentation" assay (ASBC Yeast-14) developed to detect PYF and assess fermentability or yeast strain performance. In order to detect evidence of PYF behavior, the absorbance at 600 nm of fermenting wort was used to assess yeast in suspension (turbidity). When infected with C. sativus and F. graminearum, the turbidity profile differed significantly (P < 0.01) between control and infected samples for both varieties of barley malt. The nature of the disparity was indicative of PYF behavior. Among malts that exhibited PYF, excess FAN was also observed. This is the first report demonstrating PYF behavior resulting from infection with these pathogens. Keywords: Fermentability, Fungi, Small-scale fermentation, Premature yeast flocculation, Pyrenophora teres, Cochliobolus sativus, Fusarium graminearum