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Windhab, Erich Josef
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Micro aerated food products such as Meringue, Chocolate Marshmallows or Praline fillings are of increased interest because of the greater sensorial properties, the reduced calorie density and increased thermal stability. Conventional aeration technologies are rotor-stator whipping or sparging. The clear disadvantage of these processes is the requirement of high specific mechanical energy input or costly equipment. Therefore, a novel dynamically enhanced membrane aeration technology will be developed. Here, a concentric cylinder system is present, where the inner cylinder is a solid rotating body, surrounded by an outer cylinder consisting of a sintered membrane. The sparging of the gas through a membrane with additional controlled fluid dynamics lead to a well-defined micro aerated foam. Such water-based foams consisting of a mix of egg white protein, pectin, and sugar foamed with a gas fraction up to 83% and a minimal mean bubble size of 10 μm under consideration of the rheological behaviour of the material and under variation of the applied shear rate. Elevated shear rates lead to a separation of the dispersed and continuous phase and determines the limitation of the foaming process, which can also be triggered by the application of a back pressure. A back pressure of 0.5 bar reduced the mean bubble size by 40% but with increasing back pressure an uncontrolled bubble expansion can be observed, negatively influencing the bubble size. The detachment of the gas bubble from the membrane surface determines the gas bubble size and can be nicely controlled by the flow structure in the system. Hence, the formation of Taylor vortices in the gap between the concentric cylinders enhances the bubble detachment. This results in a reduced bubble size with increasing rotating Reynolds number. The onset of such Taylor vortices was investigated using UVP. The flow analysis gives information on the influence of the cross-flow and membrane roughness in the foaming process. It was shown that the cross-flow retards the onset of flow instabilities by 4.2%. For the foaming process, it means that 4.2% higher rotational speeds have to be applied for the same effectiveness in flow behaviour detaching the bubbles from the surface. The surface roughness of the inner cylinder was investigated to simulate a membrane surface. It was shown to enhanced the onset of first flow instabilities such as Taylor vortices, leading to an improved bubble detachment efficiency Show more
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SubjectMeringue; Chocolate; Marshmallows; membrane; aerated micro foam
Organisational unit03345 - Windhab, Erich Josef
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