Program Book - Master Brewers Association of the Americas

P-201
The effects of proline-specific endoprotease (PSEP)
treatments on foam quality in beer made from various malt
varieties
JOSEPH FINN (1), Louise Robinson (2), Doug Stewart (3), Megan
Sheehy (3), Jason Eglinton (3), Evan Evans (1)
(1) University of Tasmania, Australia; (2) Lion Nathan Limited,
Sydney, Australia; (3) Joe White Maltings Pty. Ltd., Adelaide,
Australia
Both foam stability and clarity are definitive indicators of beer
quality. The perfect commercial beer has a good head and is
“brilliant”—in other words free from any haze. This image is
problematic as there is a complex interrelationship between foam
stability and haze, so that alterations or interventional treatment
in one can affect the other. The proteins involved in both foam and
haze are conventionally known to be fragments of hordeins and are
relatively rich in proline. Haze is formed when polyphenols and
hordein fragments form complexes large enough to deflect light,
thus making a beer appear cloudy. New forms of haze treatment that
specifically target proline-rich haze proteins have been developed
recently. Proline-specific endoproteases (PSEP) are enzymes that
hydrolyze proline-rich protein sequences, neutralizing the protein’s
haze-forming potential. Hordeins, however, have also been found
to be both foam-promoting and foam-reducing. A recent study by
Evans et al (J. Am. Soc. Brew. Chem., 2008, 66(1):1-10) showed
that treatment of beer with PSEP, as judged by the Rudin test, could
either slightly improve or reduce foam stability while having little
impact on beer lacing. This investigation extends these conclusions
by applying the industry standard NIBEM foam stability test. The
NIBEM test requires packaged, carbonated beer in order to assess
the influence of PSEP on foam quality. A method for small-scale
production of packaged, carbonated beer was applied successfully
and an additional trial was conducted. Using the NIBEM analysis,
the trial compared the effect on foam quality of hopping with
isomerized, against hydrogenated, hop extracts. Increasing the
levels of hydrogenated and isomerized hop extract resulted in
substantially higher levels of foam stability (Rudin, NIBEM) and
lacing (lacing index test). In all the tests, the results showed that
hydrogenated hop extract was superior to isomerized for foam
stability and lacing. According to the Coomassie blue binding and
PRM total beer protein assays the addition of PSEP does affect the
levels of haze-active and foam-active proteins. This investigation
confirmed that varieties such as Araplies, Gairdner and Sloop
have slightly improved Rudin foam stabilities while Schooner has
slightly reduced. Foam stability as measured by the NIBEM test,
however, was slightly reduced (~10 sec) with the addition of PSEP
for all four varieties. This investigation agrees with earlier research
that there are hordein fragments that are both foam stabilizing and
destabilizing. The extent to which these foam active proteins also
promote haze has yet to be established. Hordein banding patterns
are heritable characteristics of barley varieties, so the accumulated
information from the above assays may allow the selection of barley
varieties that contain hordein species that are both more foampromoting
and less haze-active. PSEP products could aid these
brewing and research objectives and prove beneficial to the brewing
industry.
In 2003 Joseph E. C. Finn graduated with a B.A. degree in English
and philosophy. After completing a minor in microbiology, he went
on to complete a studentship in the summer of 2004, researching
Bacillus cereus for the fresh-cut leafy vegetable industry. Finding a
passion for scientific research, he expanded his previous work into
a honors thesis on the microbiology of leaf surfaces and the effect
of surfactant-producing bacteria, again for the fresh-cut vegetable
industry. In 2007 he returned to research, this time taking up a Ph.D.
candidature in molecular biology, studying proteomics related to
haze in beer.
P-202
The influence of dark specialty malts on beer flavor stability
DAAN SAISON (1), Sem Vandecan (1), Freddy Delvaux (1)
(1) Katholieke Universiteit Leuven, Leuven, Vlaams-Brabant,
Belgium
Beer aging remains a hot topic in beer related science. In particular,
the role of dark specialty malts in beer flavor stability generates
contradictory evidence. Dark specialty malts are used during the
production of several specialty beer types and are responsible for the
color and typical flavor of the beers. Although several researchers
state that dark specialty malts provide antioxidants, favorable for
flavor stability, pro-oxidant capacity is also found. Color malt is
dried in a kiln at higher curing temperatures then pale malt. During
the production of caramel malt on the other hand, a two step drying
procedure in a malt roaster is applied. Due to these differences in
the production process, the chemical composition of both dark
specialty malt types differs, although the malt color is similar. In this
work the role of caramel and color malt in beer flavor stability was
studied. Therefore two 16°P amber beers of 20 EBC were brewed
using, respectively, 40 EBC caramel malt and 43 EBC color malt in a
5-hl pilot scale brewery. In order to find a correlation between beer
flavor stability and the dark specialty malt used, the concentrations
of different stale markers were monitored in fresh and aged beers
using headspace solid phase micro-extraction, coupled with gas
chromatography-mass spectrometry. Both beers were aged at
40°C for 2 and 4 weeks before gas chromatographic analysis. The
concentrations of lipid oxidation markers were significantly higher
in the aged beer made with color malt, although the concentration
of the staling indicator in the fresh beer was lower than in its caramel
malt beer counterpart. Other monitored staling compounds such
as the Strecker aldehydes 3-methylbutanal, 2-methylbutanal and
phenylacetaldehyde were also found in higher concentrations in
aged color malt beer. The Maillard reaction indicator furfural and
β-damascenone followed the same trend. By contrast, furfuryl
ethylether was higher in the caramel malt beer. The decrease of
fresh beer indicators such as isoamyl acetate and ethyl caproate
after aging was dramatic in color malt beer compared to caramel
malt beer. Staling compounds were more abundant in the beer made
with color malt. Therefore, the choice of a certain dark specialty
malt type can have a major impact on the flavor stability of the
corresponding beers.
Daan Saison graduated as a bioengineer in food chemistry and
technology at the Catholic University of Leuven. He carried out
his masters thesis at the Centre for Malting and Brewing Science at
K.U.Leuven on the subject “Characterisation of Glycoside Hydrolase
in Brewers’ Yeast and the Influence on Hop Glycosides.” After
graduation, he started a Ph.D. program at the Centre for Malting
and Brewing Science.
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