Porosity, Bulk Density, and Volume Reduction During Drying: Review of Measurement Methods and Coefficient Determinations

Several experimental methods for measuring porosity, bulk density and volume reduction during drying of foodstuff are available. These methods include among others geometric dimension, volume displacement, mercury porosimeter, micro-CT, and NMR. However, data on their accuracy, sensitivity, and appropriateness are scarce. This paper reviews these experimental methods, areas of applications and limits. In addition, the concept of porosity, bulk density and volume reduction and their evolution as a function of moisture content during drying is presented. In this study, values of initial porosity (¿0) and density ratio (ß) of some food products are summarized. It has been found that ¿0 is highly dependent on the type of food products, while ß ranges from 1.1 to 1.6. The possibility of calculating solid density based on food compositions has also been validated. The inter-predictions between porosity, bulk density and volume density have been made mathematically evident.