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A Study on the Dry-Hopping Process and Its Effects on Beer Quality 

In this study, the historical data on over 100 industrial fermentations was analyzed to investigate the differences between dry-hopped (DH) and non–dry-hopped (NDH) beers. The data collected included parameters like DAE (difference between force ferment apparent extract [AE] and packaged AE of DH and NDH beers), pH, BU (bitterness units), polyphenols, and FAN (free amino nitrogen). The results showed that DH beer had significantly higher levels of all these components except for FAN. The increase in DAE, pH, BU, and polyphenols in DH beer could be attributed to the addition of dry hops. In addition, the foam stability of DH beers was lower than that of NDH beer. The reason for this was endogenous proteases excreted by yeast cells. Furthermore, the comparison of YAN (yeast assimilable nitrogen) for NDH and DH commercial beer samples revealed that DH beer had higher levels of YAN. This suggests that the addition of dry hops can have a significant impact on the nitrogen metabolism of yeast during fermentation. To investigate this effect on DH fermentation, forced fermentations were conducted and dosed with ammonia—a constituent of YAN—at different concentrations at 0 and 18 hr to determine whether fermentations were inhibited. The results showed an increase in pH, DAE, protease, FAN, and YAN levels in DH fermentations. The results suggest that ammonia can negatively influence the fermentation process in DH beer by providing additional nitrogenous material and increasing the proteolytic activity of the yeast due to increasing pH. ​