Effects of Moisture Content and Impact Energy on the Cracking Characteristics of Walnuts

A study was conducted to determine the effects of moisture content and energy of impact on the cracking characteristics of walnuts. A sample of fresh harvested walnuts was divided into four portions and conditioned under sunshine for different time durations to obtain different levels of moisture content [9.2-29.7%, wet basis (w. b.)]. An impact test apparatus was used to apply different impact energies in the range of 0.13-1.11 J to samples with different moisture content. Data obtained on the quantity of fully cracked and unbroken kernel, fully cracked but broken kernel and uncracked nuts were used in the computation of the nuts cracking characteristics. Results showed that moisture content, impact energy and interaction effects of these two variables have significant effect on the walnuts cracking characteristics. Full cracking of nuts increased with impact energy and decreasing moisture content. The optimum moisture content for cracking walnuts that gave the best result combination of high whole kernel yield and low kernel breakage was found to be about 16%. The optimum impact energy for cracking was found to be about 1.01 J (1.01 +/- 0.1 J). The results of this study show that development of a centrifugal impact cracker, which uses impact to crack walnuts, is possible. In the designing of the walnut cracker, the radius and speed of the cracker should be such that create impact energy and velocity of about 1.01 J and 11 m/s, respectively, and walnuts should be conditioned to the moisture content of about 16% for optimum efficiency.