Program Book - Master Brewers Association of the Americas

Technical Session XIV: Premature Yeast Flocculation
Moderator: Barry Axcell, South Africa Breweries Ltd., Sandton,
Republic of South Africa
Professor Barry Axcell is group chief brewer for SABMiller. He
hold fellowships with the Royal Society of Chemistry, the Institute
of Biology, and the Institute of Brewing & Distilling. He holds
the positions of professor extraordinary in the Department of
Microbiology at the University of Stellenbosch, honorary professor
in the Department of Molecular and Cell Biology at the University of
the Witwatersrand, and special professor in the School of Biosciences
at the University of Nottingham in the United Kingdom. Barry has
authored and coauthored more than 80 papers relating to various
aspects of brewing and was the first international director of the
ASBC. He has served on the ASBC Program Committee and Journal
Editorial Board, as well as the Technical Committee of the MBAA.
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The practical hints for brewing from premature yeast
flocculation (PYF)-positive malt
YUICHI NAKAMURA (1)
(1) Nishinomiya R&D Promotion Office, Production Technology
Center, Asahi Breweries, Ltd., Nishinomiya, Japan
Premature yeast flocculation (PYF) is a serious problem in the
brewing industry. If the beer is brewed with PYF-positive malt,
yeast flocculate prematurely during fermentation while high sugar
concentrations remain and lead to a marked reduction in the
number of yeast cells. As a result, a high level of vicinal diketones
(VDKs) remains in the beer. Many researchers all over the world,
including our laboratory, are researching PYF, but the cause of the
PYF phenomenon is still unresolved. Therefore, we investigated the
brewing method for PYF-positive malt, because there is a possibility
that PYF-positive malt is supplied to our breweries. Considering the
mechanism of formation and reduction of VDKs with yeast during
fermentation and maturation, we planned two tests: green transfer
(Gruenes Schlauchen) test and high temperature fermentation and
maturation test. These tests were conducted with a 5-kL pilot-plant,
mixture of PYF-positive and -negative malt (4:6). We evaluated
these tests based on the number of yeast cells, the value of VDKs,
and the finished beer tasting. As a result of the green transfer
test, the number of yeast cells during maturation increased, the
value of VDKs decreased, and the beer taste improved. In the high
temperature fermentation and maturation test, yeasts flocculated
during maturation; however, VDKs reached a low value, and
the beer flavor improved. These technologies are applied to our
breweries and certainly make it possible for us to brew a better beer
from PYF-positive malt than before, but we have just overcome
the first hurdle of PYF-positive malt brewing. We still have many
technical difficulties to overcome these PYF problems.
Yuichi Nakamura received a M.S. degree in agricultural chemistry
from the University of Tokyo, Japan. He began employment with
Asahi Breweries, Ltd. in April 1993. After working as a researcher
in the laboratory, he was transferred to the brewing section in the
Ibaraki brewery. He studied at TU Muenchen-Weihenstephan in
Germany for one year from 2001 through 2002 and then returned to
the Nagoya brewery. He has been working in the Nishinomiya R&D
Promotion Office, Production Technology Center, Asahi Breweries,
Ltd. since October 2005.
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Factors that promote premature yeast flocculation condition
in malt
DAVID GRIGGS (1), Gill Fisher (1), Samantha Walker (1)
(1) BRI, Nutfield, United Kingdom
Flocculation is the process whereby yeast aggregate and sediment
from solution at the end of fermentation. The premature
flocculation of yeast during fermentation whilst the fermentable
sugar concentration remains high results in a marked reduction
in the number of yeast cells in suspension, leading to incomplete
fermentations, and can also extend the time required for
conditioning and maturation. Although premature yeast flocculation
(PYF) is a sporadic phenomenon, it is an increasingly important
quality issue, and some brewers are setting malt quality targets for
this parameter. PYF is widely considered to be induced in the field
when barley is grown under sub-optimal conditions, resulting in the
formation of an antimicrobial agent in response to fungal attack,
but little is known about its subsequent control or remediation.
There is also little knowledge concerning the possible influence of
malting conditions on the development of the PYF condition. The
results of research investigating the correlation between malting
process parameters and the suppression or development of the PYF
condition in finished malt are presented and discussed.
David Griggs graduated with a honors degree in industrial biology
and worked briefly in the plant biotechnology industry before
studying for his Ph.D. degree in plant biochemistry at Long Ashton
Research Station, University of Bristol. In 1990 he joined the U.K.
malting industry with first Pauls Malt then Greencore Malt, working
in a number of technical management roles. In September 2007 he
joined BRI as development director. He is both a diploma maltster
and diploma brewer. He is a past chair of the IBD Malting Barley
Committee and is a MAGB Malting Diploma examiner.
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