Graduate Thesis Or Dissertation


Investigating Hop Enzymes Public Deposited

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  • According to conventional wisdom, hops are treated in the brewery as biologically inactive ingredients, added to wort or beer primarily as a flavoring agent. In the past, hops were used in relatively small quantities, with the majority of hop additions made to boiling wort. Converse to traditional hopping practices, modern brewing techniques add hops to beer during or after fermentation, a method commonly referred to as dry-hopping. The resultant flavor profiles in each case are quite distinct; generally dry-hopping is a more delicate extraction transferring highly desirable aroma compounds to beer. Brewers seeking to increase the complexity and array of hoppy flavor in beer use generous hopping rates, blends of multiple hop varieties, concentrated hop products, and dry-hopping in the presence of yeast to increase floral and fruity flavors. As a result, a variety of unique hop-forward beers have entered the market allowing brewers to distinguish their products. An unintended consequence of everchanging brewing practices is the extraction of unknown and undesirable compounds in beer during dry-hopping. In contrast to previous thought, experiments conducted in Dr. Shellhammer’s Lab indicate that enzymes in hops survive to act on finished fermented beer, posing potential quality concerns to brewers. The addition of Cascade hops to finished beer showed production of fermentable sugars glucose and maltose as a result of starch degrading enzymes in hops. Enzyme specific assays were used to detect starch degrading enzymes in Cascade pellet hops, with the highest activities reported for amylases at 0.76 U/g. Low activity levels of debranching enzymes amyloglucosidase and limit dextrinase, were additionally found in Cascade hops, the latter of which was detected at levels below the suggested assay sensitivity. Hop enzymes were further shown to alter beer carbohydrate composition over time, with high hopping rates and high temperatures showing the greatest sugar production. The extent of over-attenuation, the loss of sugars consumed by yeast, was dependent upon the length of dry-hopping time with a total loss of 1.9°P in real extract, production of 1.3% alcohol by volume and an additional theoretical 4.75% (v/v) CO2 over 40 days of contact with hops and yeast. Differences in hop enzymatic power were found across 30 hop cultivars screened for specific enzyme activity (α-amylase, β-amylase, amyloglucosidase) and non-fermentable dextrin degradation and sugar production in beer dry-hopped with different hops. Crude hop amylase activity broadly ranged from 0.04 to 0.25 U/g of α-amylase activity, and 0.14 to 0.21 U/g of β-amylase activity. The percent change in carbohydrates in finished beer dosed with hops and antimicrobial sodium azide (0.02%) was used to profile the production of simple sugars (fructose and glucose) and small malto-oligosaccharides (maltose and maltotriose); these factors when combined accounted for 90% of the variation between hop samples. Additional hierarchical cluster analysis revealed four classifications of hops with differing abilities to hydrolyze dextrins in a control beer. However, the impact of other important factors such as harvest maturity and kilning practices should be considered in future studies. The implications of this research will change the way hops are processed and valuated, and influence how brewers select and manage hops in the brewing process. Future investigations around the factors impacting hop enzymatic power will be essential in improving hops and beer quality.
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  • Brewers Association
  • United States Department of Agriculture
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