The age-thickening of sweetened condensed milk: II. Effects of temperature and of storage

Abstract

SummaryThe rate of age-thickening of separated sweetened condensed milk increased with decreasing condensing temperature, over the range 55–22°C. Preheating the milk for 10 min at 85°C reduced the destabilizing effect of low condensing temperatures.Changes take place after condensing which have the effect of decreasing the rate of age-thickening during subsequent high-temperature storage. These changes are complete in about 2 weeks at room temperature but take longer at lower temperature.The hypothesis is put forward that the stabilizing effects of a moderately high condensing temperature, and of cool storage after condensing, are connected with the precipitation of insoluble salts, especially calcium phosphate. The effect of preheating is ascribed to the formation of nuclei of precipitated calcium phosphates which facilitates further precipitation during and after condensing.Experiments on age-thickening at a series of different temperatures with four batches of commercial condensed milk gave mean values for the temperature coefficients of increase in ‘initial’ and ‘permanent’ viscosity of 4·9 and 7·5 per 10 degC, respectively. The difference between these values is thought to support our previous conclusion that two different processes are involved.