VIEW ARTICLE DOI: 10.1094/ASBCJ-47-0077
Characterization and Mechanisms of Formation of Frozen Beer Precipitates. Hiroshi Yamashita, Satomi Fujino, Shoei Aoyagi, and Yoshihiro Tsumura, Central Research Laboratories, Asahi Breweries Ltd., 13-1 Omori-kita 2-chome, Ota-ku, Tokyo 143, Japan, and Fujitaka Hayase and Hiromichi Kato, Department of Agricultural Chemistry, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. J. Am. Soc. Brew. Chem. 47:0077, 1989.
Frozen beer precipitates were usually formed when beer was kept for several days at -8 to -13° C. The precipitates were composed mainly of β-glucans, and their molecular weights ranged from 106 to 103. The high molecular weight fraction (mol wt 106 to 105) was similar to native barley β-glucans, which have a ratio of β-(1-3) to β-(1-4) linkages of about 30:70. The medium molecular weight fraction (mol wt 105 to 104) had a ratio of about 25:75, whereas the lower molecular weight fraction (mol wt 104 to 103) was mostly composed of β-glucan with β-(1-4) linkages. In brewing barley malt, two kinds of enzymes that catalyze degradation of β-glucan were found, namely β-(1-4)-d-glucanase (I) and (II). These enzymes can also synthesize β-(1-4) linkages. For example, β-(1-4)-d-glucanase(I) is able to transfer the cellotriose moiety to the nonreducing end glucosyl residue of another oligosaccharide to form insoluble β-glucan. Lower and medium molecular weight fractions were estimated to be formed by both degradative and transferase-type reactions during the malting and mashing process. The solubility of β-glucan decreased with increasing ratios of the β-(1-4) linkage in β-glucan. In fact, the lower molecular weight fractions had lower solubilities than the high molecular weight fractions. The mechanisms of formation of frozen beer precipitates were estimated to be via increases in the alcohol concentration caused by the freeze concentration phenomenon. Consequently, the low solubility-lower molecular weight fraction precipitates and promotes the subsequent precipitation of high molecular fraction.
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