Changes in key aroma compounds during natural beer aging

Application of Aroma Extract Dilution Analysis on a flavor extract isolated from a fresh pale lager beer revealed 41 odor-active compounds among which 2-phenylethanol (sweet, flowery), 4-hydroxy-2,5-dimethyl-2(5H)-furanone (caramel-like), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (seasoning-like) and (E)-ß-damascenone (cooked apple-like) predominated with the highest Flavor Dilution (FD)-factors. In a beer sample of the same batch stored for 34 month at 20°C in the dark, the concentrations of ten of the most odor-active compounds did not change significantly. However, four compounds, namely ethyl 2-methylpropanoate and ethyl 2-methylbutanoate with fruity notes as well as the Strecker aldehydes methional (cooked potato-like) and phenylacetaldehyde (sweet, honey-like) increased by factors of 3 to 10, respectively. Based on a very precise method developed for the quantitation of (E)-2-nonenal, it could clearly be ruled out that this aldehyde contributes to off-flavor formation in the beer investigated.