The thermal load of food products during drying is an important factor fbr the final powder quality. The exposure to heat can result in the formation of insoluble material, which is undesirable especially for instant powders. It is demonstrated how to carry out experiments in order to derive a kinetic model which describes the rate of formation of insoluble material during the drying of milk. It was proven possible to achieve a good fit between the calculated values of the insolubility index obtained from an idealised model and the values obtained experimentally. This method is also suitable for other food products. The kinetic model can be used as a submodel for drying simulation models that describe the behaviour of the individual particles during spray drying. The combination of these models is an effective tool in giving indications of how to adapt industrial dryers to reduce the insolubility of the powder and get a better product quality.