SYLVIE M. DECKERS (1), Zahra Shokribousjein (1), Yannick Lorgouilloux
(1), Kurt Gebruers (1), Geert Baggerman (2), Johan A. Martens (1), Jan
A. Delcour (1), Chris W. Michiels (1), Guy Derdelinckx (1)
(1) K.U.Leuven, Heverlee, Belgium; (2) K.U.Leuven ProMeta, Heverlee, Belgium
Gushing is the spontaneous and wild over-foaming of over-carbonated
beverages that occurs at the opening of the container without any
shaking. Primary gushing is related to raw material contaminated by
filamentous fungi. These latter produce amphiphilic proteins called
hydrophobins that interact with carbon dioxide bubbles leading to
over-foaming. Up to now, to determine the gushing tendency of a malt
batch, most beer producers have used the modified Carlsberg test (MCT),
where a determined volume of sparkling water is replaced by the same
volume of an aqueous malt extract. However, the precision and the
reproducibility of this methodology have been subject to controversy.
Recently a new method based on the dynamic light-scattering (DLS)
technique was developed in our lab to characterize the primary gushing
potential of carbonated beverages. This technique was first applied only
on the final product (i.e., bottled or canned beer). It appeared that
the main difference between a gushing and a non-gushing beer was the
presence of particles with a diameter around 100 nm only in the gushing
beer. The objective of the present work was then to apply this new
method on earlier-stage products of the malting and brewing processes.
The Congress mash method was used to produce wort from non-contaminated
and contaminated malts and from a blend of non-contaminated malt and
contaminated barley. The MCT was carried out by replacing 20 mL of
sparkling water from a 1-L bottle (CO2 at 7 g/L) by 20 mL of
the worts obtained from the different malt and barley samples. After 3
days of agitation (horizontal, 150 rpm, 20°C), the bottles were opened
and the over-foaming amount was determined by weighing. The
wort/sparkling water samples were then centrifuged (4,000 × g, 10 min) and naturally degassed (i.e., at room temperature and under atmospheric pressure) until the CO2
concentration reached approx. 1.7 g/L (equilibrium value at 25°C and
under atmospheric pressure). After degassing, the size of particles
present in the different samples was determined by DLS. The MCT results
showed that worts produced from contaminated raw material (i.e.,
contaminated malt or blend of non-contaminated malt and contaminated
barley) had a clear gushing tendency and DLS allowed us to detect the
presence of particles with a diameter around 100 nm only in these
gushing samples. Our results thus tend to confirm the applicability of
DLS as a new method to characterize the primary gushing potential of raw
materials.
Sylvie Deckers received an M.S. degree in chemical bioengineering
from ULg-Gembloux Agro-Bio Tech (Gembloux, Belgium), with honors, in
2008. Her master’s thesis was on the “Possible Influence of Surfactants
and Proteins on the Efficiency of Microbiological Surface Sampling.”
Since February 2009, she has been active as a Ph.D. student at the
Catholic University of Leuven (Belgium) within the research consortium
of KULeuven-LFoRCe and M2S in the Centre for Malt and Beer
Sciences under the supervision of Professor Derdelinckx. Her topic is on
the comprehension of the primary gushing phenomenon and, more
specifically, on the interaction between CO2 bubbles and amphiphilic contaminants such as hydrophobins. In 2010, she had a paper published in Brewing Science explaining her hypothesis of the primary gushing mechanism. In 2011, she will have a paper published in the ASBC Journal containing the main results of her research.
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