Glucoamylase
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Amyloglucosidase (syn. glucoamylase; AG; AMG) is prepared from several different fungi (e.g. Aspergillus spp., Rhizopus spp.). Some preparations also contain alpha-amylase and/or transglucosidase. The latter is undesirable as it catalyses the formation, by transglucosylation, of unwanted and unfermentable oligosaccharides such as isomaltose and panose. Amyloglucosidase attacks the non-reducing ends of starch chains and dextrins releasing glucose. Its attack on alpha-(1,4)-links is comparatively rapid relative to the attack on alpha-(1,6)-links, so the conversion of starch into glucose by this enzyme is accelerated by the addition of pullulanase. The optimal pH range is 4.0–5.5, and the enzyme will act for extended periods at 60–65°C (140–149°F).[1]
The addition of glucoamylase during fermentation (as opposed to during mashing) progressively releases glucose and/or maltose, thus avoiding the inhibition of the yeast by excessive glucose concentration initially.[2]
Enzymes can be added during fermentation to increase the amount of fermentable wort sugars available in order to produce special beers with lower calories. The most effective enzyme for this purpose is the glucoamylase from the fungus A. niger. Glucoamylase (GA) is the currently accepted common name for the enzyme previously called amyloglucosidase (AG). This enzyme is capable of digesting starch or dextrins derived from starch completely to glucose (Table 10.3).[3] GA is most active at acid pH values (optimum is usually between pH 4.0 and 4.5). The enzyme is, therefore, most active at pH values found in fermentation. Under most circumstances, the addition of 5 to 10 FCC units of glucoamylase per liter of fermenting wort (600 to 1200 units per bbl) will result in maximum conversion of nonfermentable dextrins to glucose during fermentation and the maximum degree of fermentation needed to make a low-calorie beer. Toward the end of fermentation, the yeast uses the glucose formed by the enzyme almost as soon as it is released.For the complete utilization of the dextrins, the yeast should not settle from the beer too quickly. Yeast growth should be encouraged by ensuring good wort aeration and similar practices.
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References[edit]
- ↑ Briggs DE, Boulton CA, Brookes PA, Stevens R. Brewing Science and Practice. Woodhead Publishing Limited and CRC Press LLC; 2004.
- ↑ Guerra NP, Torrado-Agrasar A, López-Macías C, et al. Use of Amylolytic Enzymes in Brewing. In: Preedy VR, ed. Beer in Health and Disease Prevention. Academic Press; 2009:113–126.
- ↑ Ryder DS. Processing aids in brewing. In: Stewart GG, Russell I, Anstruther A, eds. Handbook of Brewing. 3rd ed. CRC Press; 2017.