PYF from the perspective of brewing yeast: Impacts on nutrient uptake and yeast fermentation characteristics

APOSTOLOS G. PANTELOGLOU (1), Katherine A. Smart (1), David J. Cook (1)
(1) Nottingham University, Sutton Bonington Campus, Leics, U.K.

Premature yeast flocculation (PYF) is a sporadic problem encountered during industrial brewing fermentations. Factors, thought to arise from fungal infection of barley and malt, cause yeast to flocculate prematurely and/or heavily before the depletion of available nutrients in the wort. This results in poorly attenuated worts, with higher residual extract and lower ABV, flavor abnormalities, disruption of process cycle times and potential issues with the re-use of the yeast in subsequent fermentations. Whilst previous studies have focused principally on characterizing the PYF factor(s), or on the role of fungi and/or the malting process in their generation, current research in our group aims to characterize the impacts of PYF factors on metabolizing yeast. The aim is to improve the understanding of why some breweries’ yeast strains are more susceptible to this condition than are others. An optimized PYF test based upon a 200-mL working volume was developed for the purposes of accurately differentiating PYF activity within this project (rather than as a generic screen for use by industry). Using this test and commercial PYF+ve and PYF–ve malts, it was shown that lager yeast strains differ in sensitivity toward the factor(s) in wort and that one particular strain showed no sensitivity in terms of suspended cell counts through fermentation. Yeast performance during PYF+ve and PYF–ve fermentations was compared for SMA yeast (a highly PYF-sensitive strain) using stirred miniature fermentation vessels (100 mL). In PYF+ve fermentations the peak budding index was found to be delayed (relative to PYF–ve wort), indicating changes in yeast cell-cycle progression. Furthermore there were delays in nutrient uptake in the first 12–24 hr of fermentation; specifically the uptake of free amino nitrogen (FAN), maltose, and maltotriose. Significantly lower amounts of alcohol were formed in the PYF+ve fermentations after 5–7 day


Apostolos Panteloglou holds a B.S. degree in food technology from the Alexander Technological Educational Institute of Thessaloniki in Greece (2006). After a six-month placement in the technical team of Brewing Research International (Surrey, UK) he completed an M.S. degree in food technology and quality assurance at the University of Reading (Berkshire, UK). Currently he is a Ph.D. research student at the University of Nottingham, under the supervision of David Cook and Katherine Smart, investigating the occurrence of premature yeast flocculation in the brewing and malting industries.