IMPROVING PROCESSING AND ENERGY EFFICIENCIES OF WALNUT DRYING

To improve processing and energy efficiencies of walnut drying, there is a great need to sort individual walnuts based on their moisture content before drying to increase drying capacity, reduce energy use and obtain high quality walnut products. Due to the absence of specific sorting criteria in walnut processing and drying operations, we studied moisture distribution and variability, color characteristics and physical properties of walnuts under different moisture contents (MC). Measurements were carried out for three walnut cultivars, Tulare, Howard and Chandler cultivated in California, USA. Samples from each variety were collected from the harvester at the first and second harvest with and without Ethephon treatment. The walnuts were sorted into those with a hull and those without a hull before measurement of moisture content, color and physical property measurements. The MCs of hulls, shells and kernels of selected walnuts were measured using air oven drying at 100 °C for 24 h. The CIE L, a, and b color indices were measured for the shell of nuts with and without hull, and the relationship between the color and MC was established. Several physical properties including nut mass, length, width, thickness