Investigation of New Indexes to Evaluate Aging of Bottled Lager Beer

Abstract

To determine the extent of lager beer staling accurately, six singlet analysis evaluation parameters were investigated, including 1,1′-diphenyl-2-picrylhydrazyl (DPPH) scavenging amount, N-tert-butyl-α-phenylnitrone associated with electron spin resonance spectrometry (PBN-ESR), total reactive antioxidant potential (TRAP), thiobarbituric acid (TBA), 5-hydroxymethyl furfural (5-HMF), and trans-2-nonenal, which are based on free-radical reactions and off-flavor compound formation. The singlet indexes were well correlated with natural aging time and stale-flavor taste judgment when evaluating aging beer of the same quality. However, there was an obvious limit when assessing beer samples of different quality and different degrees of aging. These singlet indexes were combined and processed by statistical analysis and mathematical methods, and complex evaluation indexes were brought forward, which resulted in a better correlation with beer aging compared with the singlet indexes. The free-radical index (FRI) was constructed based on the reactions of free-radical scavenging, and the compound index (CI) was based on the formation of stale flavor compounds. The stability index (SI) integrated the two aspects into one evaluation index using a relatively simple formula. Over the whole course of beer aging, FRI and CI increased, while SI decreased. FRI was a better predictor when measuring the moderately staled beer, which had a natural aging time of more than 90 days (or 3 months). CI was more applicable to the extremely aged beer, which had a shelf time of more than 180 days (or 6 months). To assess the general degree of beer aging, SI is put forward as a new and efficient index for beer samples at every staling stage. The research proved that complex evaluation indexes provided more applicable parameters for evaluating beer aging. Of them, SI was the best and simplest measurement for determining the extent of lager beer aging at any staling stage compared with singlet and other complex evaluating indexes.