Fate of Bitter Compounds through Dry-Hopped Beer Aging. Why cis-Humulinones Should be as Feared as trans-Isohumulones?

Abstract

The evolution of isohumulones, main bitter compound of beers, through storage and its bitter impact has been studied for many years. With the uprising of highly hopped and, especially, dry-hopped beers during the last decade, other compounds such as humulones, cis-humulinones and hulupones have been shown to participate in both the sensory and measured bitterness of these beers. However, the fate of these compounds through aging is still unclear. The present work evaluated, by means of spectrophotometric and RP-HPLC-UV analyses, the evolution of bitterness units (BU), cis- and trans-isohumulones, humulones, cis-humulinones, hulupones, and tetrahydro-isohumulones in 21 Belgian dry-hopped beers after two years of storage. Besides the expected degradation of trans-isohumulones, it was observed an average decrease of 91% of humulones and 73% of cis-humulinones. Together, these results indicate a decrease of 18 – 43% of the calculated bitterness intensity of dry-hopped Belgian beers. The losses of cis-humulinones in dry-hopped beers bring seven new oxidation compounds, some of them very similar to those issued from trans-isohumulones. The bitterness impact of these compounds is yet to be determined.

Keywords:

• Beer aging
• bitterness
• bottle refermentation
• dry-hopped beer
• humulinone

Acknowledgments

We are indebted to Brasserie d’Orval, Brasserie de Bastogne, Duvel Moortgart Brewery, Brasserie de Jandrain-Jandrenouille, AB-InBev Belgium, Brasserie d'Achouffe, Brasserie de la Senne, Brasserie St-Feuillien, Brasserie de Ranke, and Brasserie Artisanale de Namur for kindly providing fresh beer samples, and to Hopsteiner for the hulupone analytical standard.