Program Book - Master Brewers Association of the Americas

Technical Session III: Stability
Moderator: Rebecca Newman, Boston Beer Company, Boston, MA
Rebecca Newman has been involved with brewing technology
since graduating from UC Davis in 1985. She began her career as a
supervisor in quality assurance at Anheuser-Busch, moved forward
to the construction site of Hakusan Sake Brewery in the Napa Valley,
and then went on to Sierra Nevada Brewing Co., a microbrewery on
its way to becoming a regional brewery. Her career highlights include
articulation of new methods for traditional brewing practices,
being the only woman ever trained in sake brewing practices, and
lab design for new brewing operations. Analysis of raw materials,
process-based sensory evaluation, and in-line quantification
of production variables continue to challenge and invite her
participation. Currently, Rebecca works for Boston Beer Company.
She is a member of MBAA District Northern California and has held
various positions on the Executive Committee. She is also a member
of ASBC and IFT.
O-9
An extreme view or just plain old fashioned beer making? How
beer proteins suppress beer staling
PETER ROGERS (1), Frank Clarke (2), Vincent Higgins (3), Ryan
Hyland (3), Michael Jontef (1), David Duan (1)
(1) Foster’s Group Ltd., Abbotsford, Australia; (2) Griffith
University, Nathan, Australia; (3) University Western Sydney,
Campbelltown, Australia
‘Ultra-stable’ beers in our experience contain proteins (Pr-SH) that
react strongly with thiol-specific reagents. This means the proteins
are in a highly reduced redox state (ratio of thiols:disulfides is
high). Beer proteins have peroxidase activity which seems similar
to the thiol-dependent peroxidase activity operating in serum
albumin proteins. A single thiol reacts with H 2 O 2 , producing water
and converting the thiol to a sulfenic acid residue (Pr-SOH). This
oxidized residue is extremely reactive. Nevertheless provided it
occurs in a hydrophobic pocket, it is possible for the sulfenic acid
to be reduced back to the Pr-SH form. An oxidizable substrate,
like sulfite or a thiol compound RSH or even a polyphenol(s) is
required. The reaction pathway has been inferred from inhibitor
studies with dimedone a compound which reacts exclusively with
sulfenic acid residues, and by Western analysis of beer proteins
following accelerated tests. These Westerns are constructed to
react exclusively with sulfenic acid residues. This allows the cycling
between thiols and sulfenic acid moieties to be visualized. After
extended periods of ageing this occurs at a slow, albeit significant,
rate. Proteins in ultra-stable beers stay highly reduced for long
periods, well after SO 2 is exhausted (high level of reactive thiol). We
have considered whether peroxidase, superoxide dismutase (SOD),
or catalase will thus substitute for free SO 2 under these conditions
and control reactive oxygen species. Peroxidase requires an
oxidizable substrate, but converts peroxide solely to water. Catalase
destroys peroxide but, in addition to water, oxygen reappears. SOD
and catalase usually act in tandem; converting the oxyanion to water
and oxygen. Peroxidase on the other hand can eliminate oxygen
from packaged beverages. In addition to these possibilities we have
considered whether small molecules with enzyme-like activity, akin
to those above are involved in the suppression of staling in these
beers. The high molecular weight fractions prepared from beers
by ultrafiltration contain anti-ROS activity akin to conventional
catalase, SOD and peroxidase. Similarly low molecular fractions
contain catalase and SOD activity, which is heat insensitive, and is
not associated with proteins. Although there seem to be synergistic
effects when high molecular weight and low molecular weight
fractions from stable beers are combined. Both catalase and SOD
68
activity have been detected in plant extracts, notably Rosemary
extracts which are not protein based, as well as extracts from hop
varieties. We present a model in which proteins and mimetic
compounds combine to suppress ROS levels in certain beers. In the
long term we think it is preferable to retain functional protein and
to extend the donor substrates for peroxidase. We think that having
sustaining levels of oxidative substrates in beer, and retaining
protein peroxidase activity while in addition maintaining mimetic
activities, can be achieved within classic beer-making practice.
Peter Rogers is national manager of research within the Foster’s
Group’s Consumer and Category Solutions section. He deals with
strategic issues, part risk, part invention, and part new opportunity.
He is an adjunct professor at RMIT and Griffith universities. He
graduated from the Australian National University and was
involved in pioneering work on yeast mitochondrial genetics.
In keeping with his view of self as practical and empirical, he
moved progressively to biochemical value adding. He worked as a
postdoctoral fellow in Goettingen, before joining Griffith University.
He combined fundamental research with value adding in central
Queensland, the heart of cattle country. He worked at one time with
BHP, BHP Billiton these days, and prophetically, as it happened,
with steel pull-ring-tab cans. He received the Eric Kneen Memorial
Award from the ASBC in 2005 with Mark Goldsmith, and the
Presidential Award from the MBAA in 2001 with Michael Lees. He
has worked on the executive boards of several professional bodies,
including currently the EBC. His current interests are in redox
control of staling in wine and beer, and the management of wine
fermentations in an age of climate warming.