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B-420.08.041 [2020-10] Foam Stability, NIBEM

Die Schaumhaltbarkeit stellt ein wichtiges Qualitätsmerkmal dar, das einer laufenden Überwachung bedarf. Die Menge des gebildeten Schaums ist abhängig vom Kohlendioxidgehalt des Bieres, der von den Brauereien auf einen gewünschten Wert eingestellt werden kann. Die Haltbarkeit des Schaumes dagegen ist von der chemischen Zusammensetzung des Bieres (Proteinfraktion > 12.000 Dalton, Glycoproteide, Isohumulone, ß-Glucane, Metallionen) abhängig.

Application/Purpose

Determination of foam stability

Scope of Application

Beer and beer-based beverages

Principle

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
[1, 2]

NIBEM: Nederlands Instituut Brouwgerst, Mout en Bier, Dagelijkse Groenmark 3-5; 2513 AL Den Haag; Postbus 179; Niederlande

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.

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