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SCIENTIFIC RESEARCHalcohol and body 10/01/2002 Light-sensitivity of beer finally unravelled 
Beer mainly consists of water and ethanol and for the remaining part of a fraction of about 0.5% in which more than 200 different substances have been dissolved. These substances are originating from several sources, mainly from the malt, hop and yeast. During the brewing process alpha acids are formed during the boiling of the wort (see our file “brewing of beer, composition of beer”). The beer thanks its typical bitter taste to these alpha acids. Moreover, alpha acids have bacteriostatic characteristics (i.e. they slow down the growth of bacteria in beer) and they play a role in the tenability of the foam. The only disadvantage in all this is that some of these alpha acids, the iso-alpha acids, are light sensitive. As a result of this the beer develops an unpleasant lightstruck flavour and smell when it is exposed to light.Cause of this is an evil-smelling sulphur compound or thiol, also called “skunky thiol” among chemists. These evil-smelling thiols remind us of the stinking stuff that is secreted by the glands of the skunk. This lightstruck flavour was described over more than one hundred years ago, but until recently nobody knew how the chemical compounds come about. The teams of professor Denis De Keukeleire (Ghent, Belgium) and professor Colin Burns (North Carolina, USA) together found the answer. In the first place they discovered that the lightstruck flavour only occurs in hopped beers, which indicates that the hop components play an important role in the development of the unpleasant taste and smell. The scientists looked for a technique how to describe the destruction of the hop components by light. For the first time a procedure was used that is called electron paramagnetic resonance. For the first time hop experts revealed into which molecules the alpha acids disintegrate under the influence of light. It turned out that the incidence of light creates free radicals in the beer. When these free radicals meet a sulphur compound stinking thiols come about. De Keukeleire and Burns for the first time unravelled the chemical base for the lightstruck flavour of beer. Their findings can be found back in the renowned scientific trade journal Chemistry. Now it has become known how beer gets a lightstruck flavour, we can start looking for a remedy how to prevent this lightstruck flavour. And rest assured, follow-up research is already taking place. Source: Colin Burns, Arne Heyerick, Denis De Keukeleire, Malcolm Forbes. Mechanism for Formation of Lightstruck Flavor in Beer Revealed by Time-Resolved Electron Paramagnetic Resonance. Chem. Eur. J. 2001;7, no.21 | |
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