Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 1/20/2000
Publication Date: N/A
Interpretive Summary: Barley grain is made into malt, which is then used to produce beer. As part of this process, enzymes form that break down some of the large, unusable compounds of barley into small molecules that are necessary for making good beer. Sometimes barley contains proteins, called 'inhibitors', that can stop these enzymes from functioning. This usually interferes with the ability to make good beer from these barleys, but sometimes leads to better beers. This paper discusses some of those inhibitors. Three inhibitor types occur that can stop enzymes from converting unusable barley carbohydrates into malt sugars that are needed during the fermentation of beer. These inhibitors are, therefore, generally detrimental to making good beer. Two proteinase inhibitors have been studied that lower the amount of protein that is degraded into amino acids during brewing. This inhibition leads to lowered amounts of amino acids in brews, which is sometimes good and sometimes bad. Studies have been carried out to define how the inhibitors interact with the various protein-degrading enzymes and how they can affect the brewing process. The information obtained has led to the proposal of methods that can be used to manipulate the enzymes and their inhibitors to produce improved beers.
Technical Abstract: Barley contains several compounds that can inhibit the activities of various barley and malt enzymes that are crucial for brewing. This paper reviews some of the research that has been carried out on these endogenous inhibitors in our laboratory and at other locations. A proteinaceous alpha-amylase inhibitor has been purified and studied. It is present in developing and germinating grain and is coded by a single gene. Two nearly identical limit dextrinase inhibitors, coded by a single gene, are present in barley and these occur at levels that are high enough to interfere with carbohydrate degradation during brewing. A xylanase inhibitor occurs in barley, but has not yet been studied in detail. There are several small proteins in barley and in malt that inhibit malt endoproteinases. When unmalted barley is used for brewing, these can cause problems by lowering the soluble protein levels. Two of these proteinase inhibitors have been purified, characterized and identified. They tend to specifically inhibit the cysteine-class endoproteinases. Whenever malt is dissolved in water, as is done during brewing, the inhibitors form complexes with the proteinase enzymes, and these complexes cannot be disassociated without destroying the activities of the enzymes. Adding purified proteinase inhibitors to mashes lowers the soluble protein levels of the resulting wort and this method could be used commercially to produce improved beers.