Flavor stability assessment of lager beer: what we can learn by comparing established methods

Abstract

Beer is prone to flavor changes during aging that influence consumer acceptance within shelf life. The shelf life of beer is defined as the period over which flavor changes remain acceptable. Assessment of flavor changes caused by volatiles is typically achieved with a combination of sensory evaluation and gas chromatography–mass spectrometry (GC–MS). Volatile indicators causing flavor changes during beer aging are commonly determined with headspace solid–phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), or steam distillation (SD). However, discrepancies occur when comparing results from different analytical methods that affect the assessment of the degree of flavor stability. This article discusses the effect of different established analytical methods on flavor stability assessment. Reaction potentials of de novo formation, release from adducts, and degradation are hypothesized to participate in the observed discrepancies, and evidence is verified using model systems. Three extraction methods were qualitatively compared by multiple gas chromatography–olfactometry experiments (GC–O) of a one-year, naturally aged, pale lager beer. SD showed the highest number of detected aroma compounds (41), followed by HS-SPME (33), and SAFE (26). Aroma intensities for SD were more pronounced for most aging indicators than with other methods. With SAFE, only 11 aging compounds could be identified confidently, with weak aroma intensities at GC–O, and this method was thereby excluded from further experiments. Certain aging compounds were calibrated for gas chromatography-mass spectrometry (GC–MS) from HS-SPME and SD, although most compounds were present at the lower limits of detection and quantification. Relative standard deviation and recoveries for all compounds were acceptable for both methods. Quantitative comparison was conducted for four different commercial pale lager beers at different stages of aging at 20 °C (fresh, 5 months, 10 months). Aging-related changes of pale lager beer presented with altered profiles and behavior in SD compared to the non-invasive HS-SPME due to heat intake, and were borne out by GC–O results. Model systems were used to describe the impact of isolated aging-relevant mechanisms and precursors during distillation. Our findings suggest that results from different methods in reactive matrices should be compared cautiously, especially regarding aroma activity, and indicate that the most gentle or non-invasive method should be applied for analysis.