Dry-hopping, the addition of hops to beer during or after fermentation, is a common practice in brewing to impart hoppy flavor to beer. Previously assumed to be inert ingredients, recent evidence suggests that hops contain biologically active compounds that may also extract into beer and complicate the brewing process by altering the final composition of beer. Experiments described herein provide evidence of microbial and/or plant-derived enzymes associated with hops ( Humulus lupulus) which can impact beer quality by influencing the composition of fermentable and nonfermentable carbohydrates in dry-hopped beer. Fully attenuated and packaged commercial lager beer was dry-hopped at a rate of 10 g hops/L beer with pelletized Cascade hops, dosed with 106 cells/mL of ale yeast, and incubated at 20 °C. Real extract of the treated beer declined significantly within several days with a reduction of 1 °P (% w/w) after 5 days and then slowly to a total reduction of approximately 2 °P after 40 days. When fully fermented, this was equivalent to the production of an additional 4.75% (v/v) of CO2 and an additional 1.3% (v/v) of alcohol. The refermentation of beer driven by dry-hopping was attributed to the low but persistent activities of several starch degrading enzymes present in Cascade hops including amyloglucosidase, α-amylase, β-amylase, and limit dextrinase. The effect of hop-derived enzymes on beer was time, temperature, and dose-dependent. Characterizing bioactive enzymes in hops will help hop suppliers and brewers to address the unexpected quality and safety issues surrounding hopping practices in beer.
Keywords: Humulus lupulus; amylase; dry hopping; hops; maltase; over attenuation; refermentation.