Comparison of Foam Quality and the Influence of Hop á-Acids and Proteins Using Five Foam Analysis Methods

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 thought to influence foam quality. Each of the tests responded differently to beer characteristics that influence beer foam quality. The Rudin and shake tests responded positively to the level and content of foam-promoting proteins (i.e., protein Z4) and also to the level of isomerized hop α-acids in beer. However, the shake test did not differentiate between isomerized and hydrogenated hop α-acids, whereas the Rudin test did. The lacing index responded positively to isomerized hop α-acids, hydrogenated in particular, but possibly negatively to alcohol. Hydrogenation of hop α-acids and protein Z4 increased foam stability as measured by the cylinder pour test, whereas alcohol, higher pH, and CO₂ level tended to reduce foam stability. A positive association with the level of isomerized hop acids was not observed; however, further investigation is required to clarify this. Finally, the NIBEM test results were influenced positively by the level of isomerized hop acids and protein Z4, while they were negatively correlated with viscosity and final gravity. Hop α-acid hydrogenation substantially improved NIBEM foam stability compared with isomerized hop α-acids. The NIBEM test was correlated positively 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.