O-14
Prevention of protein-polyphenol haze in beer using a proline-specific protease
Presenter: Harry Craig, DSM, Delft, Netherlands
Co-Authors: Michel Lopez and Luppo Edens, DSM, Delft, Netherlands

Haze-forming activity based on protein-polyphenol interactions largely depends on the proline content of the protein fraction present. It was considered that any disruption of the proline-rich regions of these proteins would prevent the interaction with polyphenols and so prevent haze developing in beer. A highly specific proteolytic enzyme which only cleaves at the carboxy end of the proline moiety was found in a strain of Aspergillus niger. This strain has a long history of producing safe food-grade products such as enzymes and citric acid. After proving the hypothesis on a catechin/gliadin model, trials were performed at laboratory, 30 liter and 20 hl pilot plant scale, at a well-respected brewing institute using 100% malt grists. Results were compared to beers treated with PVPP. Predictive shelf-life tests, foam, reducing power, nonenal values, and flavor were assessed. Haze values and foam over a 13-month period were also checked. It would seem that the action of this protease severely limits the ability of the haze-sensitive proteins to combine with polyphenols. When added at the beginning of fermentation, dose rates are extremely low. Polyphenol levels and reducing power were higher in the trial beers, and any increase in nonenal values after incubation at 37°C for 7 days was minimal. Results were so encouraging that this enzyme is now being commercialized and undergoing trials in a number of breweries.

Harry Craig graduated in applied microbiology from the University of Strathclyde, Glasgow, Scotland, in 1970. He joined Allied Breweries Ltd. as a trainee brewer and was sponsored to study for his masters degree in brewing science at the University of Birmingham, England, under Prof. J S Hough. He then worked for Biocon Biochemicals before joining DSM in 1993. A member of ASBC and IGB, Mr. Craig travels extensively in his current role as technical manager - beer enzymes, and has much experience of a wide range of brewing materials and brewing practices.