Aaron Beattie (1), EMILY ECK (2), Mike Edney (3), Andrew J. Macintosh (2), Brian Rossnagel (1), R. Alex Speers (2)
(1) University of Saskatchewan, Saskatoon, SK, Canada; (2) Dalhousie
University, Halifax, NS, Canada; (3) Canadian Grain Commission,
Winnipeg, MB, Canada
Premature yeast flocculation (PYF) in brewing fermentations is a
concern to both the malting and brewing industries. The exact causes of
PYF are likely varied; however, it is hypothesized that exposure of
barley grains to indigenous microflora has an effect upon the behavior
of yeast cells during subsequent fermentations. In this study, the
effect of microbial contamination on barley fermentation was
investigated using small-scale assays. Two varieties of barley (CDC Bold
and AC Metcalf) were field inoculated with one of three common fungal
infections: spot blotch (C. sativus), head blight (F. graminearum), and net blotch (P. teres).
Each sample was malted, mashed, pitched, and fermented using a
high-precision mill, automated mash bash, and temperature-controlled
fermentation vessel (±0.1°C). Fermentations were performed in triplicate
using a small-scale (15-mL) assay. During each fermentation, samples
were taken at set intervals (1, 6, 22, 26, 30, 46, 50, 54, 70, 74, and
78 hr). Yeast turbidity was spectrophotometrically assessed at 600 nm
while apparent extract was determined through density measurements of
the wort. It was found that the final turbidity (linked to yeast in
suspension) differed significantly (P > 0.05) between most
control and infected samples. In the fermentation of most
fungal-infected malts, the data show turbidity peaking sooner and
declining more quickly than the control malt. It was also found that the
degree of difference from the control correlated very well with
established susceptibilities of the barley varieties to the introduced
fungal species. In general, CDC Bold, which is reported to possess ‘very
poor’ resistance to all three fungi, exhibited poor yeast in suspension
behavior when infected. AC Metcalf, which is ranked higher than CDC
Bold in resistance to these fungi, exhibited little or no PYF behavior.
For example, CDC Bold, when exposed to F. graminearum, showed a
peak in turbidity 12 hr earlier than the control and declined to less
than half the turbidity by 78 hr when exposed to that fungus.
Conversely, AC Metcalf, when exposed to C. sativus, displayed no significant (P
> 0.05) change in turbidity versus its control. The observed changes
to yeast in suspension are consistent with the phenomenon of premature
yeast flocculation. Given that these fungal infections appeared to
trigger PYF in laboratory studies, further examination is warranted.
Emily Eck is a research technician at Dalhousie University in
Halifax, NS, Canada. In 2010 she completed her B.S. degree in
environmental science and economics at Dalhousie University and the
University of King’s College. Since 2009, she has been working in the
Dalhousie brewing laboratory under the direction of Alex Speers. Her
current research is focused on malt fermentability and small-scale
fermentation assays.
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