The importance of considering exchange surface area reduction to exhibit a constant drying flux period in foodstuffs

In this study, experimental data on the shrinkage of potato, carrot, apple and avocado using high-speed laser scan micrometers are presented. These devices allow the exchange surface area to be evaluated at any time. Results of convective drying trials show consistently that a constant drying flux period does exist provided the actual exchange surface area is considered. Most numerical models tend to neglect the shrinkage factor for case of solving the model equations. We have shown in this study that such an approach is only valid for products that have a very small shrinkage factor. In the case of foodstuffs with high initial moisture content and therefore having a high tendency to shrink, the model must incorporate the shrinkage factor for it to reflect the reality. Using these experimental values, a critical moisture content, very different from that generally proposed in the literature, was exhibited. (C) 2002 Elsevier Science Ltd. All rights reserved.