A mathematical model was adapted to predict the movement of moisture in a bed of sucrose when a temperature gradient is applied. The model results were successfully compared against experimental results for different temperature gradients. Previously reported work on liquid and solid bridges demonstrated that caking occurs in sucrose when the relative humidity (RH) of the air in contact with the sucrose particles exceeds 80%. The model was used to predict what temperature gradients were needed to induce sufficient moisture movement within a bed of sucrose for the 80% RH conditions to be exceeded. A chart that shows the relationship between the temperature of the sugar when it is packed, the environmental temperature and the water activity of the sugar was constructed. This can be used as a guideline to ensure moisture movement from temperature gradients in sugar masses does not induce caking, either during transport or storage in silos. (c) 2008 Elsevier Ltd. All rights reserved.