Measuring the tensile strength of caked sugar produced from humidity cycling

Abstract

The aim of this study was to develop moisture migration modelling in stored sugar due to the temperature cycling of the storage environment. This was done by forming cake of sugar in a gas-bearing tensile tester. The sugar and tester were enclosed in a controlled humidity system and the relative humidity was cycled between four hours at 70 per cent relative humidity and four hours at 20 per cent relative humidity. Liquid bridges formed between the sugar particles at high relative humidity, with the bridges hardening subsequently when the humidity was reduced. It was found that the relationship between the tensile strength and number of cycles could be approximated by the relationship σT = K √ N and the agglomerate tensile strength was in the order of 150Pa after 32 cycles. This suggests a soft cake rather than hard cakes with a tensile strength of twice this order of magnitude, which are formed, for example, in salt. A value of 1300kPa was obtained for the parameter representing the average strength of the bridge material in a simplified model of monosized spheres linked by pendular bridges in a system of uniform packing.