THE PREPARATION AND SOME FLOW CHARACTERISTICS OF PLASTIC CASEIN

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Abstract
The preparation of rennet casein has been studied on both a laboratory and plant scale, and the effect of the various factors in procedure on the quality of the casein produced is discussed. The details of preparation for a product of excellent quality are given. A simple heat resistance test showing the presence of impurities has been developed. The plasticity of a number of caseins has been measured by a direct method in a laboratory extruder, under pressure ranging up to 77,000 lb. per sq. in.; the maximum viscosity measured directly in this study was about one billion, seven hundred million poises. The flow-pressure curves obtained show no tendency towards a yield point, but show varying degrees of structural viscosity and may be fairly well represented by the relation F = kPn, where F is the flow, P is the pressure, n and k are constants. Decrease in pH of the casein, decrease in ash, and increase in lactose content all lower the viscosity of plastic casein. Small increases in water content decrease the viscosity greatly. Up to 80 °C. the temperature of drying has no appreciable effect on the viscosity. Moistening of casein plastic is discussed, as is also the distribution of water and vapor equilibria. Plastic casein is shown to exhibit streamline flow in extrusion, and plasticization is therefore more difficult to accomplish.

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