Matthias Baldus (1),
Sarah Majetschak (2), Frank-Jürgen Methner (2); (1) Technische
Universität Berlin, Berlin, Germany; (2) Technische Universität Berlin,
Institute of Food Technology and Food Chemistry, Lab of Brewing Science,
Berlin, Germany
Technical Session 4: Barley & Malt I
Sunday, August 14 • 2:00–3:15 p.m.
Tower Building, Second Level, Grand Ballroom
Dimethyl sulfide (DMS) is one of the most investigated undesirable
aroma compounds in beer. Malt contains significant amounts of its
oxidized form dimethyl sulfoxide (DMSO). DMSO cannot be removed via
evaporation and survives the brewhouse, acting as DMS precursor during
fermentation. The actual source of DMSO in malt and wort has not been
investigated in detail. In this study different species of reactive
oxygen in combination with the transition metal ions iron (Fe(II)) and
copper (Cu(II)) were investigated for their oxidation ability and
quantity of DMS in model solutions. Moreover the impact of malt
endogenous reducing substances (sulfite, thiols, polyphenols and
reductones) was tested. The results show that molecular oxygen hardly
produced any DMSO during 5 hr of incubation at 80°C. DMS oxidation and
concomitant DMSO formation increases with the following composition:
Fe(II)+O2 < Cu(II)+O2 < H2O2+Fe(II) < H2O2.
The added reducing substances showed an overall prooxidative behavior
that could eliminated by EDTA overshoot for every substance except for
polyphenols and sulfite. This indicates an direct reduction of molecular
oxygen by the latter substances, whereas the other substances seem to
recycle metal ions into their reduced state, keeping them available for
hydrogen peroxide formation via the Fenton reaction. The observations
could be further confirmed by comparison of hydrogen peroxide formation.
Peroxidic oxygen is proposed as the most likely source of DMS
oxidation. The pro-and antioxidative effect of certain reducing
substances is further discussed based on redox kinetics and recycling
ability of transition metal ions. The results of this work are of
fundamental importance for initial approaches to DMSO minimization in
malt, wort and beer.
Matthias works as scientific assistant at the Technische
Universität Berlin at the Chair of Brewing Science. He apprenticed as a
brewer and maltster at a middle-sized brewery in Germany before he
studied biotechnology and brewing technology. He graduated from his
studies as a Diplom-Ingenieur. During this time he investigated grist
fractionation methods to optimize the lautering process. Moreover, he
evaluated thermal desorption processes to optimize volatilization of
undesired aroma compounds. Matthias is currently working on his
dissertation, which is focused on sulfuric substances in the brewing
process, especially on DMS and its precursors. In addition, he is
working on optimization techniques for the brewhouse process.
