Abstract

The precise and objective estimation of the beginning of gelation in milk is topical for both laboratory studies and industrial dairy production. In this work, the principles of the thermographic method of monitoring milk coagulation are formulated. This method has evolved from the well-known hot-wire method; it is based on the measurement of the temperature difference between two thermometers, one of which is heated. Unlike the hot-wire method, the thermographic method can even be used in processes that require significant changes in milk temperature, for example, during heat–acid milk coagulation. Two basic designs of thermographic systems, using as thermometers either differentially connected thermocouple junctions or two identical thermistors connected as two legs of a bridge circuit, are described. In both cases, the temperature difference between the heated and unheated thermometers at about 0.5 W of thermal power supply is about 3°C for incoagulated milk and 8–10°C after clot formation. The qualitative agreement of the results of rheological and thermographic methods has been demonstrated. A thermographic research technique for heat–acid or heat–calcium milk coagulations has been developed. Within the effective viscosity model, the numeric solution of the problem of temperature field simulation in the vicinity of the heated thermometer has been obtained. On the basis of the simulation results, the possibility of studying structure formation in milk during its coagulation has been analyzed using the thermographic data. Experimental results obtained during thermographic research of milk coagulation are presented.

Keywords

milk coagulation control, heat convection, thermographic method

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