Comparison of foam quality and the influence of hop-a-acids and proteins by five foam analysis methods

The Rudin, NIBEM, lacing index, cylinder pour and shake foam quality tests were comprehensively compared to evaluate their utility and responsiveness to beer components that are regarded to influence foam quality. It was found that each of the tests responded differentially to beer characteristics that influence beer foam quality. The Rudin and shake tests were found to respond positively to the level and content of foam promoting proteins (i.e., protein Z4) and also to the level of isomerised hop-a-acids in beer. However, the shake test did not differentiate between isomerised and hydrogenated hop-a-acids while the Rudin test did. Lacing index was found to respond positively to isomerised hop acids, hydrogenated in particular, but negatively to alcohol. Hydrogenation of hop acids and protein Z4 increased foam stability as measured by the cylinder pour test while alcohol, higher pH and CO2 level tended to reduce foam stability. A positive association was not observed with the level of isomerised hop acid, but further investigation is required to clarify this. Finally, the NIBEM test results were influenced positively by the level of isomerised hop acids and protein Z4, while negatively correlated with viscosity and final gravity. Hop acid hydrogenation substantially improved NIBEM foam stability compared to isomerised hop acids. The NIBEM test was positively correlated with the Rudin, cylinder pour, lacing index and shake (foam quality generated) tests. These comparisons and observations suggest how these foam quality evaluation tests may be best used for quality control/assurance and beverage development.