Dynamically enhanced membrane foaming

Foamed food products like chocolate mousse, ice cream or fresh cheese are increasingly popular due to their soft and creamy sensory properties. Their perception, stability and flow behavior strongly depend on gas fraction and bubble size distribution. Foam processing research focuses on developing new optimized processes and material systems to achieve small mean bubble size and narrow size distribution. In this work, we present a new dynamically enhanced membrane foaming process. This foaming device basically consists of two concentric cylinders: the inner cylinder is rotated with circumferential velocities up to 30 ms(-1), the outer cylinder is fixed. Thus, a shear field is created in the narrow annular gap. The membrane can either be mounted to the inner or outer cylinder. Gas is pressed through the membrane and is detached as small bubbles by the acting flow shear stresses. The comparison of rheological and microstructural analysis of foams to results on bubble breakup in simple shear flow and on detachment of bubbles from the pore of a rotating membrane proved that the detachment of small bubbles from the membrane is the dominating bubble formation process in the dynamically enhanced membrane foaming process. Compared to conventional rotor-stator foaming devices, the dynamically enhanced membrane foaming process leads to significantly smaller mean bubble sizes at higher gas volume fractions and to reduced size distributions widths. (c) 2007 Elsevier Ltd. All rights reserved.