Milk foam optimization for the creamiest cup of cappuccino
Mhmm … what was a delicious cup of cappuccino without lots of smooth and creamy milk foam ?! – Of course , the good feel in the mouth and long-lasting foam stability are not left to chance . When designing a new cappuccino powder , food scientists elaborately puzzle out the best formulations . They have to choose the right ingredients and mix them in optimal proportions and with the most suitable techniques . Emulsifiers and foam stabilizers play a very important role here . They are needed to lower the surface tension , which , in the first place , allows the formation of the milk foam . Moreover , they tune the ‘ viscoelastic properties ’ of liquid surfaces which are especially important with regard to the foam ’ s stability .
STUDY OF SURFACE TENSION AND VISCOELASTICTY
The surface tension of a liquid can easily be measured in a pendant drop experiment . The OCA system from DataPhysics Instruments returns the result within seconds . One finds , for example , that caseins , which possess good foaming and emulsifying properties , distinctly lower the water surface tension . This happens because these food proteins are surface-active , meaning they adsorb to the water surface and form there a self-assembled layer . However , as the
54 FDPP - www . fdpp . co . uk food scientists want to learn more about the stabilizing effect of the caseins , they must also study the viscoelasticity of the protein layer .
Quite conveniently , the indicated surface rheological experiment can be carried out directly with the OCA measuring system at hand . The required oscillating drop method is just a few clicks away – and there is not even the necessity to change any part of the instrumentation . In order to determine the elastic and the viscous proportions of a sample ’ s surface ( or interfacial ) layer , DataPhysics Instruments ’ electronic syringe module periodically increases and decreases the pending drop ’ s volume and , hence , its surface area . At the same time , it is monitored how the surface tension reacts to these changes .
OSCILLATING DROP EXPERIMENTS
In these experiments one observes that the measured surface tension follows the change of the surface area – either directly , or with a certain delay : That depends on the disability , or ability , of the surface-active molecules in the surface layer to quickly adsorb to and leave the surface . If there is a high exchange of molecules between the bulk solution and the surface ( because the molecules try to compensate surface depletion or over-population caused by the drop enlarge- and diminishment , respectively ) the measured surface tension follows the surface area changes with a distinct delay , or ‘ phase shift ’. Such a finding attests rather viscous surface properties ; as is reflected by obtaining a comparably high surface dilatation viscosity modulus , E ’’. On the other hand , if the molecules are adsorbed irreversibly at the surface , the surface tension reacts directly to
any changes of the surface area : As soon as it increases the surface tension also increases , because less molecules are available per unit surface area , and vice versa . One says such a surface layer behaves ‘ elastic ’, and measures a high surface dilatation elasticity modulus , E ’.
High surface elasticity has been correlated with low coalescence rates and is , besides a low surface tension , hence desirable with the objective to generate stable foams . The calculation of the surface dilatation moduli , just as the execution of the whole experimental procedure , is of course automatically performed by DataPhysics Instruments ’ software . So , there is time to lean back and enjoy another cup of creamy cappuccino .
Understanding Interfaces