Beer haze clearing up: Barley proteins implicated in sediment formation

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  • Published: Oct 15, 2011
  • Author: Steve Down
  • Channels: Proteomics
thumbnail image: Beer haze clearing up: Barley proteins implicated in sediment formation

Nothing like a good pint

Some of us reckon that there is nothing like a good pint at the end of a long working day. Unfortunately, we are occasionally given a drink that is, literally, nothing like a good pint. A beer blighted by haze or sediment just cannot be enjoyed quite as much as a clear drink that you can see your fingers through.

Cloudiness in beer is one of the quality defects that brewers strive to eliminate during manufacture because it can drive beer drinkers from their brands if they encounter a "bad pint." So, there has been a considerable amount of research into the causes of beer haze.

The principal contribution to haze is derived from the formation of complexes of proteins with polyphenols. Most malt proteins and polyphenols are removed during the various beer processes of wort boiling, fermentation, maturation and filtration but a number remain.

Some of these are essential to beer quality, like the formation of head foams, but others combine to form colloids in solution responsible for the haze, with malt proteins from the hordein family strongly implicated.

A team of Chinese scientists has now examined the fate of proteins throughout the brewing process with a view to characterising their roles in the formation of beer haze.

Bei Jin and colleagues from Zhan Jiang Normal University, South China University of Technology, Guangzhou, and the Guangzhou Zhujiang Brewery Group Company, published their findings in the Journal of Food Processing and Preservation.

The samples of malt, wort, fermented wort and beer were acquired from a local brewery. The proteins were extracted from each type of material and from the beer haze and separated by one- and two-dimensional gel electrophoresis..

Hazy results

Comparison of the 1D profiles showed that the number and abundance of proteins decreased as the brewing process progressed from malt to beer, although there were some consistencies. For instance, a protein at molecular mass of about 40 kDa was observed in all samples and was attributed to protein Z, a water-soluble protein found in barley malt.

The protein patterns from wort were similar before and after boiling with the exception of water-soluble proteins in the high-molecular-mass region, which were absent after boiling. This might be due to their loss during processing or dissociation into smaller proteins.

Most wort proteins were also detected in beer but at reduced abundances. Similarly, the proteins extracted from beer were largely present in the haze matter, but at markedly decreased abundances.

The resolution of 1D SDS-PAGE was insufficient to resolve the proteins for identification, so the researchers turned to 2D gel electrophoresis, with mass spectrometric identification of the proteins of interest.

Contrary to published reports, Jin found that the hordeins originating from malt were only minor components of the beer haze. Specifically, hordein gamma3, hordein B and storage protein (Hordeum vulgare) were identified but their low abundances implied that they were not significant contributors to the haze. It was confirmed that most hordeins did not survive during brewing.

The major haze proteins were identified as barley trypsin inhibitor CMe protein, germin E and protein Z. These are protease-resistant proteins that are also thermally stable due to their internal disulphide bonds, so that they remain intact during beer production. They contain relatively few proline residues, compared with the proline-rich hordeins.

Their role in haze development in beer and their possible interactions with the hordeins are unclear but their discovery points to a novel mechanism of haze formation.

Future research into the fate of proteins during the brewing process and the specific involvement of these haze-forming proteins could lead to more efficient brewing procedures and the consistent production of better beers.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

 A proteomics study following proteins through the brewing process has suggested that the haze found in beers originates predominantly from barley proteins, rather than the hordein proteins in malt that had previously been implicated 

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