Program Book - Master Brewers Association of the Americas

O-50
Improvement of premature yeast flocculation (PYF) caused by
PYF-malt using tannic acid
MAO SUGIHARA (1), Osamu Oogane (1), Saori Yamauchi (1),
Takeo Imai (1), Yutaka Ogawa (1)
(1) Research Laboratories for Brewing, Kirin Brewery Company,
Limited, Yokohama-shi, Japan
Premature yeast flocculation (PYF) is a phenomenon whereby
factors in malt (PYF-malt) cause yeast to flocculate during
fermentation when fermentable sugar is still present in the wort.
As a practical countermeasure, breweries could consider adding
a blend of non-PYF malt; however, there are limits to the volume
of non-PYF malt that could be blended in, and the resulting longterm
storage of PYF-malt in the brewery would lead to long-term
silo occupation and to degradation in malt quality. In this study, we
noted that PYF improved with the addition of gallotannin or other
tannic acids to the wort or yeast. To examine this phenomenon, we
have conducted several fermentation trials by changing the amounts
of tannic acids added, the timing of addition, and the type of tannic
acids used. Our results indicated that the addition of tannic acid at
appropriate levels (under 4.0 g/kg malt when added to wort; under
0.20 g/kg yeast when added to yeast slurry) increased the number of
yeast cells during the middle and late stages of fermentation and also
resulted in improved extract consumption. To obtain the desired
effect, tannic acid is added to wort before or after pitching yeast
(hot wort, cold wort) or can be directly added to yeast slurry. The
greater the amount of tannic acid coming in contact with yeast cells,
the greater the improvement in fermentation. On the other hand,
excessive amounts of tannic acid (more than 4.0 g/kg malt when
added to wort, or more than 0.2 g/kg yeast when added to yeast
slurry) indicated a negative effect. Therefore, to obtain the desired
improvement in fermentation, it is important to properly control the
amount of tannic acid introduced, and the timing of its introduction.
Improved fermentation was observed for tannic acids in general
(hydrolysable tannin and condensed tannin), of which gallotannin,
tara tannin, gallic acid (hydrolysable tannin) and persimmon
tannin demonstrated particularly prominent effects. The degree of
improvement differed according to the tannic acid used. Our data
suggest that longstanding problems caused by PYF derived from
PYF-malt can be addressed by using certain tannic acids.
Mao Sugihara graduated from Hiroshima University in 2001
with a M.S. degree in fermentation technology and joined KIRIN
Brewery as a brewing staff member at its one of its largest plants
in Toride. After four years in production, he joined Research
Laboratories for Brewing in Yokohama as a researcher responsible
for yeast physiology. His research interests are new strain screening,
fermentation process development, and improvement. Recently he
started working in beer filtration.
90
O-51
Continuing investigations on malt causing premature yeast
flocculation
JOSEPH LAKE (1), R. Alex Speers (1)
(1) Dalhousie University, Halifax, NS, Canada
Premature yeast flocculation (PYF) is a recurring problem in
breweries worldwide. There are many negative fermentation effects
attributed to PYF factors, which ultimately lead to beers of low or
unacceptable quality. However, due to its sporadic nature, much
needed research concerning PYF (with the exception of Japanese
and South African researchers) has either not been undertaken
or has remained proprietary. Consequently, many questions still
abound with regard to the causes and mechanisms of PYF. It is
suspected that PYF is induced by compound(s) originating in
the malt, surviving through the brewing process and interacting
with brewing yeast, resulting in their early removal from the
fermenting medium. The nature of this compound (or compounds)
is still debated, and many different factors (such as arabinoxylan,
β-glucan and ferulic acid) have been described in the literature
as being PYF inducers. Previously, we have presented (ASBC
Annual Meeting, Victoria, BC, 2007) experimental data for a
series of filtrations of wort mashed with PYF-positive malt. The
PYF wort was filtered through both a 0.45 µm membrane and a
100 kDa membrane prior to fermentation with a small volume
(15 mL) test tube fermentation. It was found that filtration of
PYF wort through a 100 kDa membrane reduced PYF activity (as
evidenced by absorbance and Plato measurements) compared with
the 0.45 µm filtered and unfiltered PYF wort. In continuation of
this research, retentate from the 100 kDa PYF wort filtration was
collected and inoculated back into ‘control’ wort for analysis via
small volume test tube fermentations. It was confirmed that PYF
was induced in an otherwise normal wort through the addition of
the 100 kDa PYF retentate. Conversely, retentate (100 kDa) from
‘normal’ fermenting wort did not induce PYF when reintroduced
to a ‘control’ wort prior to fermentation. In order to determine
potential active components of the 100 kDA retentate several pure
suspect compounds were added to ‘control’ wort and fermented.
The addition of pure arabinoxylan (medium molecular weight) did
not induce PYF. Additions of ferulic acid and β-glucan (medium
molecular weight) had variable influence upon addition to ‘control’
wort. We will report on the screening of this isolated factor and tests
conducted to determine the nature of the active component(s) in the
100 kDa retentate.
Joseph Lake obtained a honors co-op B.S. degree in marine
biology from Dalhousie University, Halifax, NS, in 2004. Joseph
is currently working toward a Ph.D. degree in food science and
technology at Dalhousie. Under the supervision of Dr. Alex Speers,
his research focus is premature yeast flocculation but also includes
other yeast/fermentation topics. In the summer of 2005 Joseph had
the opportunity to spend four months in industry at Prairie Malt
Limited, in Biggar, SK, examining topics in barley and malt. He
plans to graduate in late 2008 or early 2009.