Foam stability represents an important quality attribute of beer and therefore must remain under constant scrutiny. The amount of foam formation is dependent on the carbon dioxide content of the beer, which can be adjusted to the value desired in the brewery. On the other hand, the capacity for foam formation and the stability of the foam are dependent on the composition of the beer (protein fractions > 12,000 Da, glycoproteins, iso-humulones, β-glucans, heavy metals).
Determination of foam stability
Beer and beer-based beverages
Determining foam stability using a NIBEM foam stability tester entails the time in which the surface of a head of foam collapses in a
standardized cylinder. Four separate phenomena cause foam to collapse:
| Coalescence: | the fusion of two bubbles |
|
Disproportionate pressure: |
diffusion between bubbles due to pressure differences in the bubbles |
|
Drainage: |
liquid exiting the foam |
| Diffusion of other gases: |
the creation of an equilibrium between the gas in the bubbles and the ambient air |
A movable system of electrodes tracks the surface of the foam (foam level) by means of electrical conductivity. One long needle is immersed in the center of the foam. The electrodes descend until one of the four outer needles touches the surface of the foam, at which point the electrodes stop their downward motion. The electrodes are motionless until contact to the outer needles is broken as the foam collapses, whereupon the electrodes begin their downward motion once more until they again come into contact with the foam. A timer built into the device measures the time for the foam to collapse (10/20/30 mm). After the measurement is completed, the electrode system returns to its initial position and the measured value is displayed in seconds.
NIBEM: Nederlands Instituut Brouwgerst, Mout en Bier, Dagelijkse Groenmark 3-5; 2513 AL Den Haag; Postbus 179; The Netherlands