Program Book - Master Brewers Association of the Americas

Poster Session: Premature Yeast Flocculation
Moderator: Fateh Sodha, Molson-Coors Brewing Company, Golden,
CO
Fateh Sodha is the process manager in the Brewing Department
at Coors Brewing Company. In his 10 years at Coors Brewing
Company, he has worked in the chemistry and microbiology labs,
quality control, and as the fermentation and yeast manager. Fateh
has a B.S. degree in anthropology, with an emphasis in biology,
and a M.S. degree in medical anthropology from the University of
Colorado, and he recently sat for his diploma in brewing exam. He is
a member of IBD and ASBC.
P-183
Investigation of the causes of PYF malt using a modified
analytical method for the PYF potential
KATSUYA SASAKI (1), Hiroshi Yamashita (1), Katsunori Kono (1),
Yasushi Kitagawa (1)
(1) Asahi Breweries Ltd., Moriya-shi, Japan
Premature yeast flocculation (PYF) is a serious problem in the
brewing industry because it causes low attenuation and results in
an undesirable flavor in beer. The PYF phenomenon is induced
by certain malts, which we call “PYF malts.” To overcome the
PYF malt issue, it is important to study in detail the relationship
between the actual malting conditions and the PYF potential of
the malt using reliable analytical methods. Our approach to the
PYF issue is presented here in three stages. 1) Development of a
reliable analytical method for PYF potential: there have been several
analytical methods for estimating PYF potential. However, they
frequently have problems with repeatability because of unstable
fermentation. We found that putting in a boiling stone or similar
object to release the CO 2 dissolved in the fermentation wort made
small-scale fermentations stable. High repeatability was obtained
on a 50-ml scale fermentation, and this allowed us to carry out a
quantitative analysis. In addition, we succeeded in developing a 3-ml
scale fermentation test in a spectrophotometer cuvette. This has
advantages for research in which many samples need to be analyzed
at the same time. 2) Investigation of the causes of PYF malt: our
studies on the localization of PYF factors and micromalting tests
using infected barley suggest that one of the causes might be
infections from microorganisms on the barley. We screened more
than thirty kinds of fungi from the PYF malt and investigated
which of them caused PYF in the malt. Malts made from barleys
infected with five strains of fungi were shown to be PYF positive,
and the fungi were identified. In parallel with this, the influence
of steeping conditions on PYF were investigated in a micromalting
facility. Steeping with no aeration increased the PYF potential
compared with aeration. 3) Monitoring of the PYF potential of
all the malt samples shipped in 2006–2007: the PYF potential of
every malt sample shipped was routinely analyzed using a 50-ml
scale fermentation test. We will report the frequency of PYF malt
found among them. We observed that PYF malts were produced
continuously from certain malting plants, even when no PYF malt
was found in other malting plants using barley from the same area.
This suggests that in addition to the quality of the barley, the malting
process is also an important factor.
Katsuya Sasaki is a research worker at the Research Laboratories
of Brewing Technology, Asahi Breweries, Ltd. in Ibaraki, Japan.
He received his M.S. degree in engineering from Tokyo Institute
of Technology in 1998 and joined Asahi Breweries, Ltd. He has
researched malt quality and malting technology.
156
P-184
A new method to measure yeast flocculation activity in
malt using lectin (concanavalin A) coated quartz crystal
microbalance (QCM)
HIDEKI TSUDA (1), Masahiro Gomi (1), Takeo Imai (1), Atsushi
Murakami (1), Yutaka Ogawa (1)
(1) Kirin Brewery Company Limited, Research Laboratories for
Brewing, Yokohama, Japan
Premature yeast flocculation (PYF) is the phenomenon whereby
yeast flocculates prior to depletion of nutrients in the wort.
Because this interferes, PYF causes low attenuation and results
in an undesirable flavor in beer. PYF is caused by a substance
called premature yeast flocculation-inducing factor (PYF-factor)
in malt. It has been reported that PYF-factor is a high molecular
weight polysaccharide. Nevertheless it is very important for
brewers to measure yeast flocculation activity or to detect PYF
activity in malt, only a fermentation test has been applied as the
conventional method for a long time. A fermentation test is a test
wherein the actual fermentation is performed with wort and yeast
in a small scale taking into account yeast growth and gravity of the
wort. A fermentation test is a kind of bio-assay, results from the
fermentation test fluctuate and are influenced by the yeast condition
and nutrients in wort. In order to dissolve this problem, many
devices or protocols have been developed. However, a new method,
which does not need yeast and fermentation, has never been
reported. Therefore, we have developed a new method to measure
yeast flocculation activity in malt without using a fermentation test.
This method is very unique because yeast flocculation activity is
measured using Concanavalin A coated quartz crystal microbalance.
Concanavalin A is a lectin purified from Jack bean (Canavalia
ensiformis). It has been reported that Concanavalin A has an affinity
to PYF-factor. Quartz crystal microbalance (QCM) uses the nature
of the quartz crystal which has a characteristic frequency that
decreases regularly when something binds on the quartz crystal
surface. We made a QCM sensor coated with Concanavalin A. Our
method is composed of four steps: 1) the malt extract is prepared
from the congress wort by the conventional HPLC technique,
2) a Concanavalin A coated QCM sensor and the malt extraction
are mixed in the acid buffer, 3) the frequency of the QCM sensor
changes (decreases) responding to the amount of the PYF-factor
included in the malt extraction, and 4) the frequency change
during 60 seconds is defined as the yeast flocculation activity in
the original malt. As a result of the test with nine malt samples, the
yeast flocculation activity measured by our method correlated well
with that measured using a fermentation test. Using our method, we
were able to measure the yeast flocculation activity or to detect PYF
activity in malt without yeast and fermentation.
Hideki Tsuda received a M.S. degree in agricultural chemistry from
Tohoku University in Sendai, Japan. He entered Kirin Brewery
Company, Ltd. in April 1993. After working in the malting and
brewing area, he was assigned to the Research Laboratory for
Brewing in 2004.