Instability of Hop-Derived 2-Methylbutyl Isobutyrate during Aging of Commercial Pasteurized and Unpasteurized Ales

Abstract

The current article is concerned with the instability of 2-methylbutyl isobutyrate (2-MBIB) throughout beer storage. 2-MBIB is the primary ester of hops and HS-SPME-GC-MS/MS analysis of 135 commercial ales confirmed that 2-MBIB is also one of most abundant hop-derived volatiles in ale. To investigate 2-MBIB stability during beer aging, eleven domestic ales with initial 2-MBIB levels ranging from 10 − 311 µg/L were analyzed across freshly packaged, naturally and forced aged beer. Upon storage, 2-MBIB concentrations in all ales decreased remarkably. After 24 weeks at 20 °C the tested ales lost 80% of their initial 2-MBIB concentration on average. At 4 °C, which is considered an ideal beer storage temperature, the average reduction was still 60%. Overall, the lowest 2-MBIB reduction was found in pasteurized ales, indicating that 2-MBIB decrease is driven by chemical and enzymatic reactions. The losses of 2-MBIB appear to be a significant contributor to the chemical instability of hoppy ales.

Keywords:

• Analysis
• ester
• flavor
• flavor stability
• hop aroma
• hops
• mass spectrometry

Acknowledgments

The authors wish to thank the breweries for providing ale samples and the German Federal Ministry for Economic Affairs and Energy for funding this research. Nils Rettberg thanks Nea Thörner for being (incredibly) patient while this manuscript was prepared.

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This research was funded by the German Federal Ministry for Economic Affairs and Energy. Data presented herein is part of the project “Flavor stability of hoppy ales” (grant number VF170007). The instrument used for HS-SPME-GC-MS/MS analysis of hop aroma compounds is part of grant number 49IZ180038.