Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 21, 2001
Publication Date: N/A
Interpretive Summary: During the malting and brewing processes, the proteins of barley and malt must be partially broken down. Enzymes, called proteinases, form during malting and carry out this process. The amount of protein that is broken down depends on how much of each of these enzymes is present. To make good beer, some but not all, of the protein needs to be degraded. None of the proteinases are inactivated during malting, but nearly all are destroyed during brewing. This paper reports our studies on when the enzymes were inactivated during brewing. During the early, low temperature, brewing stages the proteinases were stable, so the proteins were presumably rapidly hydrolyzed. When the temperature of the brew was raised to 70C to help release sugars, the proteinases were quickly inactivated, and within 16 minutes the protein-degrading enzymes were no longer functioning. Brewers can use this information to either increase or decrease the amount of protein that is present in beer, which can be important to them. This work shows that they can cause more protein to be solubilized by extending the early, low temperature, steps, but that lengthening the 70C stage will not affect the protein levels.
Technical Abstract: During malting and mashing, the proteinases of barley and malt partially hydrolyze their storage proteins. These enzymes are critical because several aspects of the brewing process are affected by the soluble proteins, peptides and/or amino acids that they release. To develop improved malting barleys and/or malting and brewing methods, it is imperative to know whether and when the green malt endoproteinases are inactivated during malting and mashing. These enzyme activities are totally preserved during kilning and, in this study, we have determined when they were inactivated during mashing. Samples were removed from experimental mashes that mirrored those used in commercial breweries and their endoproteolytic activities were analyzed. The malt endoproteinases were stable through the 38C protein rest phase, but were quickly inactivated when the mash temperature was raised to 72C for the conversion step. All of the proteinase activities were inactivated at about the same rate. These findings indicate that the 'soluble protein' levels of worts can be varied by adjusting the protein rest phase of mashing, but no by altering the conversion time. The rates of hydrolysis of individual malt proteins probably cannot be changed by altering the mash temperature schedule, since the main enzymes that solubilize these proteins are affected similarly by temperature.