The Interaction Between Malt Protein Quality and Brewing Conditions and Their Impact on Beer Colloidal Stability

In bright beers, the formation of permanent haze is a serious quality problem that places limitations on the storage life of the product. From silica gel, used for the colloidal stabilization of beer, a silica eluent (SE) protein fraction was isolated and an antibody raised against this fraction. Sodium dodecyl sulfate‚-polyacrylamide gel electrophoresis (SDS-PAGE) immunoblot analysis using the SE antiserum detected a range of protein bands in barley, malt, beer, and haze. Interestingly, a polymorphism was observed in some barley varieties that contained an ~12,000-molecular-weight band (SE +ve), while in other varieties, this band was absent (SE ‚-ve). Pilot brewing trials found that beer brewed from SE ‚-ve varieties formed less haze in haze force testing trials (5 days at 55¬∞C/1 day at 0¬∞C) than did beer produced from SE +ve varieties. The interaction between the presence/absence of the SE protein and controlled-atmosphere brewing by brewing under nitrogen or air was also investigated. Surprisingly, the application of a nitrogen-rich atmosphere produced beer that was less stable compared with that produced when brewing under a normal atmosphere. Filtration trials showed that the colloidal stability of beer could be influenced by the filtration process. The removal of the SE protein and other proteins during filtration from beer brewed with an SE +ve malt variety, along with a reduction in the level of total protein as measured by Bradford, resulted in improved colloidal stability. Combined, these investigations are discussed in terms of brewers' options for extending the colloidal stability of their beer and optimizing the colloidal stabilization treatments.