When a consumer picks up a pint of cold beer, it is generally recognised that four factors influence his or her perception of quality: colour, flavour, foam and clarity. Although this latter parameter, clarity, may be achieved through the effective removal of yeast following fermentation, the clarity of beer may also be influenced by the presence of proteins combined with secondary plant products known as flavanols. Flavanols are naturally occurring polyphenolic compounds in barley malt and hops, which remain in the finished beer to an extent which is dependent on the brewing processes used. When flavanols combine with beer proteins, colloidal particles may be formed, which are large enough to scatter light (a little like dust particles seen in a shaft of sunlight) and these may confer a hazy appearance on the beer. Although this haze is harmless, it is generally regarded as undesirable in ale and lager beers. Brewers therefore seek to control the concentration of flavanols in beer through the use of highly reproducible brewing processes.

Researchers from the University of Ulster at Jordanstown, in a CAST (Co-operative Award in Science & Technology) project, have been working with Guinness to develop biosensors for the detection of flavanols in beer. The technology is based on the use of an enzyme which reacts with flavanols to indirectly measure the concentration of these substances in beer. A naturally occurring plant enzyme (in this case polyphenol oxidase) is incorporated in a polymeric matrix, which is then used to construct an electrode which may be immersed in the beer sample to be analysed. The reaction of flavanols in the beer sample with the entrapped enzyme generates a measurable current, which is proportional to the concentration of flavanols in the sample.

The sensor developed has been successfully applied to the analysis of beer samples, producing results which agreed with more established (but less rapid) analytical methods. It has also been demonstrated that the sensor may be used in an on-line capacity, enabling very rapid analysis of beer during production. It is hoped that, in future, brewers will be able to control flavanol levels in beer to a greater accuracy than before as a result of the application of this new technology. The end result, we hope, is more satisfied consumers who get a perfect pint every time.

   * University of Ulster at Jordanstown
** Guinness Research and Development, Dublin