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The Editors regret the long delay in the publication of this paper, due to complex administrative difficulties) SUMMARY. The action of rennet on the stability of casein micelles has been described theoretically by combining Michaelis-Menten enzyme kinetics with von Smoluchowski's theory for slow coagulation. The casein micelle is considered to be stabilized by stcric interactions arising from a highly hydrated surface protein layer. The stability factor, in von Smoluchowski's theory, is then considered as a variable and determined by the concentration of unhydrolysed K-casein.The theoretical approach describes semi-quantitatively experimental observations on clotting time (CT) as a function of temperature, rennet concentration, and total protein concentration. The model also predicts that, under certain circumstances, the CT is inversely proportional to the enzyme concentration. Furthermore, the model agrees with other workers' experimental observations on the effect of /c-cascin concentration, the presence of a lag phase, and that the lag phase is commonly about 60% of theCT.

The stability of chocolate milk, made from two different cocoa powders and skim milk, was studied. Three types of instability could be distinguished: sedimentation of cocoa particles, formation of large flocs and formation of light and dark coloured layers (segregation). From adsorption studies and rheological measurements it could be deduced that chocolate milk behaves as a fluid with a weak network. The cocoa particles themselves are incorporated in this network structure. This network is formed by an interaction of protein and protein-covered cocoa particles in the presence of a suitable stabilizer (carrageenan). Heat treatment has a considerable effect on the interactions. Segregation is supposed to be caused by uniaxial compression of the total network due to gravitational force, and segregation will stop when the gravitational force is counterbalanced by the elastic modulus multiplied by the deformation gradient of the network. The compression may be influenced by the adherence of the network to the container wall.

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