BACKGROUND: Recently, a new process concept has been proposed to selectively adsorb wort off-flavours, i.e. aldehydes, from alcohol-free beers with hydrophobic zeolites. RESULTS: In this work, we investigated the uptake of a mixture of wort flavour compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, furfural, and methional), from a model solution onto binderless hydrophobic ZSM-5 zeolite granules in order to quantify mass transfer parameters and identify bottlenecks. Subsequently, the homogenous solid diffusion model was employed to regress the effective diffusion coefficients for each molecule and experimental condition, which ranged between 10⁻¹⁵ and 10⁻¹³ m² s⁻¹, indicating strong intraparticle mass transfer limitation. Furthermore, it was found that the effective diffusion coefficient is inversely correlated to the molecules' hydrophobicity, expressed as the logD value and its isotherm affinity constant. CONCLUSION: These results give valuable insight to design and improve the adsorbent material and an off-flavour removal unit at industrial scale.

The increasing popularity of alcohol-free beers (AFBs) fosters the industry interest in delivering the best possible product. Yet, a remaining sensory defect of AFBs is the over-perception of wort flavour, caused by elevated concentrations of small volatile flavour compounds (i.e. aldehydes). Previously, molecular sieves (hydrophobic ZSM-5 type zeolites) were found most suitable to remove these flavours by adsorption with high selectivity from the AFBs. In this work, a flavour-improved beer is produced at pilot-scale using this novel technology, and its chemical composition, sensory profile and stability are evaluated against a reference. Aldehyde concentrations in the flavour-improved product were found 79–93% lower than in the reference. The distinct difference was confirmed with a trained sensory panel and could be conserved even after three months ageing at 30 °C. Future work will focus on the process design to scale up this technology.