THE QUANTITATIVE MEASUREMENT OF FOAM STABILITY

Abstract

As the originators found, beer foam in pure CO₂ in the Blom or Rudin apparatus shows a straight-line logarithmic decrease. Other workers, attempting to copy practical conditions, have found non-straight line decreases. This we explain as due to foaming the beer in air and so to incorporation of variable proportions of air in the foam. In the short term this does not cause oxidation of the bubble films, but a progressive increase occurs in the proportion of air in the bubbles at the foam surface leading to progressive lengthening of bubble life. This is because the diffusion of air outwards is much slower than that of CO₂. When impure CO₂ is used in the Blom or Rudin apparatus increased values and the same departure from straight-line logarithmic fall can be shown. In such cases meaningful half-life values cannot be calculated. We have therefore used a modified Rudin method with pure CO₂ and have obtained consistent and meaningful results with a lower degree of variability.