Beta-glucan measurement and control.

MBAA TQ 1978, 15(2), 102-105 | VIEW ARTICLE

Lyons, T.P.

Beta glucans of barley are a group of linear polysaccharides consisting of glucose units linked by beta 1,3(30%) and beta 1,4(70%) bonds. Molecular size ranges from 20,000 to 1 million daltons. Barley beta glucan content lies between 1.5 and 2.5%. In well-modified malt the level is 0.15 to 0.3%. A 1% solution of highly purified barley beta glucan had a specific viscosity of 20 to 30 cps at 30 degrees C. Viscosity increased almost logarithmically with concentration. High wort viscosity in the mash tun leads to run off difficulties. The beta glucan content of malt and the level of beta glucanase activity may be controlled to a considerable extent in the malting process but the stability of malt beta glucanase is poor at normal infusion mash temperatures. At 65 degrees C some 99% of the activity is lost after 1 min. Heat stable microbial beta glucanase, able to withstand 60 min at 65 degrees to 70 degrees C and with a high endo beta 1,4 glucanase activity can achieve a significant reduction in wort viscosity, decreasing run off time and improving extract. High molecular weight beta glucan in beer, particularly high gravity beer, may give precipitates and filtration difficulties. Microbial beta glucanase, either alone or with papain, added at conditioning stage can overcome these problems. The 'break' achieved on boiling wort in the copper removes beta glucan as well as protein. Removal of beta glucan was enhanced by addition of carrageenan copper finings. The reduction averaged 15 to 20% at 27 ppm carrageenan. Beta glucan levels in wort and beer were determined by precipitation with 30% (W/V) ammonium sulphate, washing with ethanol, followed by hydrolysis of the precipitate with sulphuric acid and determination of glucose by the anthrone method.
Keywords: barley beta brewing glucan glucanase gums mashing stabilisation wort boiling  


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