Since we first began reporting on PYF in 2006 (and collaborating with Drs. Evans and Bowman shortly thereafter) there has been a reoccurring research interest in malt induced premature yeast flocculation or PYF. A 2006 KPMG report estimated losses of $10x10⁶ CDN per occurrence in the Canadian market alone. The worldwide phenomenon is most likely often under reported but was estimated to occur every five years at a minimum. It is noteworthy that PYF is difficult to discern at low levels and is obscured by the variation of the Apparent Extract (AE) and Yeast in Suspension (YIS).
In this presentation we will discuss: (1) improvements to the ASBC Yeast-14 PYF assay; (2) methods to measure PYF behaviour while considering the heteroscedastic (i.e., non-normal) variation of AE and YIS values; (3) the effect of fungal infection of barley and malts and (4) the effect of crop year/variety. The Yeast-14 assay was improved (halving yeast propagation time and eliminating the wort oxygenation stage in the Yeast-14 procedure. We devised a more rapid and efficient assay and illustrates that PYF detection is capable using other industrial lager yeast strains with slight changes to the method. Not surprisingly, the levels of C. sativus and F. graminearum, barley variety (AC Metcalfe, CDC Copeland, Norman and Excel) and crop year significantly influenced the PYF/turbidity profiles (P< 0.01) of control and infected samples for varieties of barley malt.