Moisture transfer in solid food materials: A review of mechanisms, models, and measurements

Drying is one of the most important processes in the food industry, as well as one of the most frequently studied topics in food engineering. Optimizing this process will result in lower production costs and increased product quality. Moisture transfer in heterogeneous materials, such as foods, is a complex process where more than one mechanism may occur. After over eighty years of applying Fick's Second Law diffusion equation to drying of foods, there are still wide variability in reported diffusion coefficients. This article reviews moisture transfer mechanisms, models developed to predict moisture transfer, measurement of effective moisture diffusivity, which is the most common parameter used in predicting moisture transfer, and advanced measurements of moisture profiles to quantify and validate predictive models.