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
s.
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.
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