Influence of high concentrations of aldehydes added at mashing-in on beer flavor stability: no evidence for direct contribution to aged beer aldehydes

Abstract

Aldehydes are key markers of beer flavour stability, however, their origin during brewing and ageing remains debated, particularly with respect to de novo formation and release from bound-state forms. The present study investigated whether aldehydes present at the mashing stage contribute to the pool of free aldehydes in beer after fermentation and ageing. A mixture of selected aldehydes (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, methional, phenylacetaldehyde, furfural, hexanal, and trans-2-nonenal) was added at mashing-in at concentrations corresponding to 3-fold and 10-fold levels relative to those quantified in a reference mash.
Beers were produced in pilot scale and aldehyde concentrations were analysed in fresh samples and after 90 days of forced ageing at 30 °C using HS-SPME-GC-MS. The addition of aldehydes at mashing-in did not result in increased concentrations of free aldehydes in fresh beer. After forced ageing, all variants exhibited comparable aldehyde levels, and no consistent dose–response relationship between initial and final aldehyde concentrations was observed. These findings indicate that aldehydes present at early stages of brewing do not persist as a direct source of free aldehydes in finished or aged beer. The results indicate that aldehyde levels in aged beer are primarily determined by reactions occurring during storage, particularly Strecker degradation and other thermally driven pathways, rather than by the initial concentration of free aldehydes in the mash.