Designing a drying process for oak acorns focused on energy usage and the quality characteristics of the final product

Any changes in the process pattern should consider the amount of energy consumption, process time, and product quality because they have an impact on the price of the final product. In this research, drying process of acorn was studied. The whole acorn takes longer to dry due to its hard shell and low moisture diffusivity, which leads to an increase in energy consumption; the shell's adhesion to the kernel makes it difficult to remove shell from the moist acorn. Therefore, three processing methods were examined: one-stage drying (drying whole acorn), two-stage drying (short-term drying of whole acorn, peeling and re-drying of kernel), and roasting-drying (initial roasting of whole acorn, peeling and drying of kernel), with the aim of decreasing drying time and energy consumption. The results indicated that the roasting-drying method had a 61% lower energy consumption than the one-step drying method. This method led to less quality changes in the final product, including color changes, shrinkage, and true density. Using 80°C as a critical temperature resulted in the highest moisture diffusion in the acorn. Therefore, the best process pattern for drying the valuable acorn product is roasting-drying at 80°C.