MBAA TQ https://doi.org/10.1094/TQ-59-3-1202-01 | 
VIEW ARTICLE
Paul H. Chlup, Chanita L. Gentry, Lauren J. Mercado, and David Avram. Great Central Brewing Company, Chicago, IL, USA
Abstract
Free amino nitrogen (FAN) and yeast assimilable nitrogen (YAN) levels significantly increased after dry hopping in four commercial fermentations. The introduction of nitrogenous material, such as ammonia, inhibited amino acid (L-arginine) absorption and resulted in fermentations slowing down. Throughout the dry-hopping process, shear forces from pumps cause yeast stress, increasing protease excretion from the cell. The protease hydrolyzes medium-sized peptides into smaller peptides that are metabolized by yeast. It is hypothesized that the nitrogenous material that is comprised of FAN and YAN in conjunction with exogenous proteases increases due to environmental stress and contributes to slow fermentations, over-attenuation, and reduced foam stability.
