Submitted to: Brewers Digest
Publication Type: Abstract Only
Publication Acceptance Date: June 20, 1998
Publication Date: N/A
Technical Abstract: During the malting and brewing processes, the insoluble barley storage proteins must be partially degraded to obtain a wort that will ferment into acceptable beer. As part of our ongoing study of how barley storage proteins are enzymatically degraded into soluble proteins, peptides and amino acids during malting and mashing, we are characterizing the malt endoproteinases and their endogenous inhibitors. We reported last year that the endoproteinases that form during malting are nearly all stable to kilning and to the protein rest portion of mashing, but were rapidly inactivated when the temperature was raised to 65C. Now, we are studying the endoproteinases that are active during mashing by preparing ASBC mashes (Malt method 4), removing samples at various times and studying the proteinases present. We have found: 1) the endoproteolytic activity of the mash is strongly inhibited by the class-specific protease inhibitors PMSF, EDTA and E-64, indicating that serine, metallo- and possibly cysteine proteinases are involved; 2) the activity is markedly activated by cysteine and by various buffers; 3) it is inactivated by the addition of 'endogenous' inhibitors prepared from barley or kilned malt and; 4) whenever the endoproteinase activity of the mashes was altered by these compounds, corresponding changes occurred in the soluble protein levels of the resulting worts. The 'soluble protein' levels of worts can be altered significantly by the addition of chemicals to mashes.