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.

中文翻译：

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大型啤酒的风味稳定性评估：通过比较已建立的方法可以学到什么

啤酒在陈酿过程中易于变味，影响消费者在保质期内的接受度。啤酒的货架期定义为风味变化保持可接受的时间。通常通过感官评估和气相色谱-质谱联用（GC-MS）的组合来评估由挥发物引起的风味变化。通常通过顶空固相微萃取（HS-SPME），溶剂辅助风味蒸发（SAFE）或蒸汽蒸馏（SD）来确定导致啤酒陈酿过程中风味改变的挥发性指示剂。但是，在比较影响风味稳定性评估的不同分析方法的结果时，会出现差异。本文讨论了不同建立的分析方法对风味稳定性评估的影响。假设从头形成，从加合物释放和降解的反应势能参与了观察到的差异，并使用模型系统验证了证据。通过一年自然老化的淡啤酒的多次气相色谱-嗅觉试验（GC-O）定性比较了三种提取方法。SD显示出检测到的最多的香气化合物（41），其次是HS-SPME（33）和SAFE（26）。与其他方法相比，大多数衰老指标的SD香气强度更为明显。使用SAFE，可以可靠地鉴定出11种老化的化合物，而GC–O的香气强度很弱，因此该方法被排除在进一步的实验之外。某些老化的化合物已通过HS-SPME和SD进行了气相色谱-质谱（GC-MS）的校准，尽管大多数化合物的检测和定量下限较低。两种方法均可接受所有化合物的相对标准偏差和回收率。对四种不同的商业淡啤酒在20°C（新鲜，5个月，10个月）的不同熟化阶段进行了定量比较。与无创HS-SPME相比，由于热量摄入，与淡啤酒有关的衰老相关变化在SD中具有变化的特征和行为，并由GC-O结果证实。模型系统用于描述分离过程中与老化有关的机理和前驱物的影响。我们的发现表明，应谨慎比较反应性基质中不同方法的结果，尤其是在香气活性方面，