Batch stripping of flavour active compounds from beer: Effect of dry matter and ethanol on equilibrium and mass transfer in a packed column

Physiochemical similarities of volatile compounds and their interactions with the beer matrix are the main challenging factors in selective separation of ethanol for the production of non-alcoholic beer and removal of excess (off-)flavours produced during fermentation, such as isoamyl acetate. In this paper, we are especially interested in the effect of beer dry matter, a complex mixture of carbohydrates and proteins, and of ethanol on flavour behaviour during treatment with a packed bed column using CO₂ as a stripping agent. By analysing the gas phase at different dry matter concentrations, we observed that its’ presence is a facilitating factor for ethyl acetate and isoamyl acetate release, whereas isoamyl alcohol is retained in the liquid phase. These effects are a result of combined mass transfer effects and affinity for carbon dioxide, which are both affected by the presence of ethanol in the feed stream. Mass transfer analysis of isoamyl alcohol and ethanol revealed that the resistance is not controlled by their solubility in water but the affinity to CO₂.