Flavour instability of beer is a concern for brewers and has been investigated over many decades. Despite advancements in the characterisation of changes during the ageing process of pale lager beers (PLB), research on the flavour instability of non-alcoholic beer (NAB) -a beer style becoming increasingly prevalent on the market -is lacking. This study characterises the main chemical-analytical changes during a forced ageing process (90 days at 30°C) of seven commercially available NAB and compares the findings to the aged seven PLB counterparts. The major differences from ageing were increased concentrations of aldehydes and decreased levels of glutamine and esters, which occurred to the same extent for both beer styles. However, trans-iso-α-acids underwent a greater decrease in aged NAB, likely due to the lower pH of this style. Furthermore, correlations between ageing parameters in aged and fresh beers, previously found in PLB (Strecker aldehydes and corresponding amino acids, relative decrease of trans-iso-α-acids and pH) are confirmed and were also valid in NAB. Interestingly, sensory analysis revealed that aged NAB showed lower overall ageing scores, compared to aged PLB. This might be explained by differences in the formation of aldehydes causing worty off-flavours during ageing. In summary, this study provides a detailed overview of the ageing process of non-alcoholic beers in comparison with pale lager beers, which could help brewers to develop more flavour stable beers.

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