The aim of the this experiment was to learn working principles of batch type of tray dryer its application in drying of wet marrow to obtain information about falling rate period, constant rate period, equilibrium moisture content, free moisture content of drying periods, and total drying time was calculated according to results which measured during the experiment on the tray dryer.
Drying is defined as that unit operation which converts a liquid, solid or semi-solid food material into a solid product of significantly lower moisture content. Drying is a complex process involving simultaneous heat and mass transfer (D. Salunkhe, H. Reddy 1991). In most cases, drying involves the application of thermal energy, which causes to evaporate into the water phase (except freeze drying). Microorganisms that cause food spoilage and decay cannot grow and multiply in the absence of water. Also, many enzymes that cause chemical changes in food and other biological materials cannot function without water. When the water content is reduced below 10% (wt), the microorganisms are not active. It is usually necessary to lower the moisture content below 5% (wt) in foods to preserve flavor and nutrition. The requirement of thermal energy, phase change and a solid final product properties distinguish drying operation from mechanical dewatering, evaporation, distillation, adsorption and osmotic dewatering. Foods are dried commercially starting from either their natural state (vegetables, fruits, milk, grains) or after processing (instant coffee, whey, soup mixes).