The Effects of Polyphenols Extracted During Dry Hopping on Flavor Stability of Beer

Dry hopping is a method of imparting aroma and flavor into beer. Hops --- the flower of the female perennial, Humulus lupulus --- are sometimes added into beer --- and especially ales --- after fermentation for a period of time to extract flavor-active compounds and give the beer a characteristic hoppy aroma. This process has been employed for hundreds of years and is called dry hopping. There are accounts from the nineteenth century of that speak to the use of hops post-fermentation in cask ales. These accounts do not speak of dry hopping as a method of flavor production but rather a method of preservation. Hops were added for their antiseptic and preservative qualities and it is here where this current work focuses. Hops contain many compounds like flavan-3-ols and humulones that can act as antioxidants as well as having antimicrobial properties. Both of these attributes allow beer to benefit from hops with regards to flavor stability. The concentration of polyphenols in hops is relatively high when compared to that of barley. Although hops are added into beer at a rate of approximately 1:100 with respect to malt, they can contribute upwards of 20-30% of the total polyphenols in the finished beer.;Polyphenols in dry hopped beer were characterized and quantified by RP-HPLC-MS/MS in both young and aged beers. These data were compared against two beer flavor stability markers --- aldehyde formation and the ratio of trans/cis -iso-alpha-acids (t/c ratio). Comparative aldehyde profiling was performed by solid phase microextraction (SPME) GC/MS. The t/c ratio was determined by RP-HPLC/DAD after successful separation of all six iso-alpha-acids present in conventionally hopped beer. Lastly, sensory descriptive analysis was performed on both the young and aged beers and statistically compared to the chemical analysis with multiple factor analysis.