foods Article Impact of Dry Hopping on Beer Flavor Stability Bradley M. Titus 1 , Larry A. Lerno 2 , Jordan W. Beaver 3 , Nadia K. Byrnes 2 , Hildegarde Heymann 2 and Anita Oberholster 2, *   Citation: Titus, B.M.; Lerno, L.A.; Beaver, J.W.; Byrnes, N.K.; Heymann, H.; Oberholster, A. Impact of Dry Hopping on Beer Flavor Stability. Foods 2021, 10, 1264. https://doi.org/ 10.3390/foods10061264 Academic Editor: Maurizio Ciani Received: 23 May 2021 Accepted: 30 May 2021 Published: 2 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Food Science and Technology, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA; bmtitus@ucdavis.edu 2 Department of Viticulture and Enology, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA; lalerno@ucdavis.edu (L.A.L.); nkbyrnes@ucdavis.edu (N.K.B.); hheymann@ucdavis.edu (H.H.) 3 Department of Chemistry and Biochemistry, University of Texas at Tyler, 3900 University Boulevard, Tyler, TX 75799, USA; jbeaver@uttyler.edu * Correspondence: aoberholster@ucdavis.edu; Tel.: +1-(530)-754-4866 Abstract: To investigate the chemical and sensorial impact of dry hopping time on typical pale ale, a standardized beer was produced and separated into ten vessels. Nine vessels were dry hopped, and one vessel remained un-hopped as a control. Impact of dry hopping contact time was investigated over 96 h. Polyphenols and iso-α-acid t/c ratio were analyzed in both Young and Aged beer samples. Total polyphenol content generally increased in both young and aged treatments compared to controls. Analysis of the t/c ratio suggests that both Young and Aged beers were chemically preserved to some degree after approximately 12 h at the given dry hopping rate regardless of age. Within the Aged beer trials, 96 h of dry hop contact yielded a significant increase in t/c ratio compared to all other Aged trials. This suggests that a 4-day dry hop regime may yield additional oxidative protection of iso-α-acids in beers stored unrefrigerated for 30 days. Descriptive analysis was also performed with an 8-person, trained panel; however, beers were sensorially distinguished by their aging time as opposed to their dry hopping time. Keywords: beer; dry hopping; flavor; stability; iso-α-acids; polyphenols; sensory 1. Introduction Hopping can occur at multiple points during beer production, with each point of addition imparting different hop qualities to the beer. The addition of hops during the boil is primarily used to impart bitterness, as the active aroma compounds evaporate out of solution as a function of wort temperature, environmental pressure, and exposure time to the boiling wort (i.e., addition time) [1]. Hopping later during the boil time or after flame-out often imparts more aromatic qualities of the hops, as the lower temperatures retain the volatile oils in solution more effectively [2] (pp. 133–135). “Dry hopping” is a method of potentially imparting even higher concentrations of aroma into the finished beer without contributing significantly to bitter taste. This occurs when hops are added post-fermentation, allowing aroma compounds to slowly extract into the alcoholic solution while minimizing extraction of bittering acids from the solid material due to the lack of high heat [3]. While modern dry hopping is primarily used to impart beers with the characteristic hoppy aroma, earlier work from the eighteenth century describe dry hopping as a method preserving the freshness and flavor of beer, as well as limiting microbial growth [4]. The stability of beer flavor, as well as how beer chemistry contributes to flavor stability, has long been a subject of interest to researchers. As many of the hop-derived compounds-such as polyphenols, humulones, and iso-α-acids-act as antioxidants and demonstrate antimicrobial properties, it can be expected that they will have some effect on flavor stability and the aging potential of beer. While the exact nature of beer flavor stability Foods 2021, 10, 1264. https://doi.org/10.3390/foods10061264 https://www.mdpi.com/journal/foods