THE INFLUENCE OF ETHANOL ON THE FOAMING PROPERTIES OF BEER PROTEIN-FRACTIONS - A COMPARISON OF RUDIN AND MICROCONDUCTIVITY METHODS OF FOAM ASSESSMENT

The effect of ethanol on the foaming properties of beer protein fracti ons was studied using a microconductivity method and nitrogen gas to g enerate the foam. Increasing the ethanol concentration resulted in a d ecrease in foam stability. Interfacial studies including thin film dra inage and dilational elasticity measurements indicated that ethanol re duced the rigidity of the adsorbed protein layer resulting in accelera ted drainage from the foam lamellae and increased probability of film rupture. These results conflict with data from the Rudin method (using nitrogen gas to generate the foam) which indicate that, at low concen tration, ethanol improves foam stability. These apparently conflicting results may be explained by the foam positive effects of a decline in bubble size and increase in bulk viscosity observed for the Rudin met hod, contrasted with the negative influence of a reduction in surface viscosity observed for the microconductivity foam assessment method.