Ethanol modulates the influence of beer constituents on foam stability and interfacial properties

Non-alcoholic beers exhibit lower foam stability than their alcoholic counterparts, diminishing their quality. This study investigates the influence of ethanol on foam stability and how ethanol alters the foam-related effects of selected beer constituents. A non-hopped alcohol-free beer was enriched with iso-alpha-acids, arabinoxylan, and high molecular weight beer molecules (mainly proteins and carbohydrates). These samples were prepared with and without the addition of ethanol. Subsequently, the foaming properties and interfacial behaviour of these samples were investigated, and the concentration of these components in the foam was determined. Results indicate that ethanol generally decreases foam stability. Ethanol promoted drainage and reduced the viscoelasticity of the air/water interfaces, leading to increased coalescence and/or disproportionation. Furthermore, ethanol diminished the positive impact of iso-alpha-acids on foam stability by lowering the incorporation of iso-alpha-acids into the foam. This study reveals that decreased foam stability in non-alcoholic beers is not caused by the absence of ethanol.