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

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 mu g/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 degrees C the tested ales lost 80% of their initial 2-MBIB concentration on average. At 4 degrees 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.