Although present in concentrations in microgrammes per litre level, aldehydes, in particular those derived from Strecker degradation, are known to majorly contribute to the undesired wort flavour of alcohol-free beers. In order to improve currently available products, one needs to understand the underlying cause for the over-prevalence and identify leverage points and methods to selectively reduce the aldehydes in alcohol-free beers. This work gives a short overview on relevant flavour-active wort flavours identified in alcohol-free beer and on their involved chemical formation pathways. Consequently, aldehyde removal technologies in general and in brewing industry are presented. Adsorptive removal of off-flavours by aldehyde-scavenging groups is already widely exploited in the packaging industry and may achieve reduction of these components to near depletion, depending on the process conditions. Its principles are adaptable to recovering off-flavours before filling. Also, supercritical CO₂ extraction has been successfully applied to separate flavours from food matrices. In brewing, the focus has been set to biologic conversion by restricted fermentation steps, but the reduction of key components of more than 70% is not achieved. Newer developments focus on thermal separation techniques that not only include non-specific physical dealcoholisation but also more selective technologies such as pervaporation, where aldehydes are reduced to near depletion. However, for most unit operations, selectivity and capacity are not yet investigated. Future research should explore the shortcomings of current techniques and overcome bottlenecks either by developing more specific methods for aldehyde removal and/or a clever combination of unit operations to optimise the separation and process integration.

中文翻译：

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醛作为无酒精啤酒中的麦芽臭味的来源和控制

尽管醛的浓度以微克/升为单位，但已知醛，尤其是衍生自Strecker降解的醛，主要导致了无酒精啤酒的麦芽汁不良味道。为了改善当前可用的产品，需要了解过度流行的根本原因，并确定杠杆作用点和方法，以选择性地减少无酒精啤酒中的醛类。这项工作简要概述了无酒精啤酒中鉴定出的具有相关风味的麦芽汁风味及其涉及的化学形成途径。因此，提出了一般和酿造工业中的醛去除技术。通过醛清除基团吸附去除异味已在包装工业中得到广泛利用，并且取决于工艺条件，可以实现将这些组分减少到几乎耗尽的目的。它的原理适用于在填充之前回收异味。另外，超临界CO₂提取已成功应用于从食品基质中分离风味剂。在酿造中，重点已经放在通过限制的发酵步骤进行生物转化上，但是关键成分的减少没有达到70％以上。较新的进展集中在热分离技术上，该技术不仅包括非特定的物理脱醇，而且还包括更具选择性的技术，例如全蒸发，其中醛被减少至接近耗尽。但是，对于大多数单元操作，尚未研究选择性和容量。未来的研究应该探索当前技术的缺点，并通过开发更具体的醛去除方法和/或巧妙地组合装置操作以优化分离和工艺集成的方法来克服瓶颈。