Eastern black walnuts (Juglans nigra L.) were collected weekly in September and October to identify a method to determine the optimal harvest date and to develop a quantifiable color classification system for kernels. Husk hardness, measured by a durometer, decreased over a 5-week period. During the collection periods, the greatest percent kernel for ‘Emma K’, ‘Kwik Krop’, and ‘Sparrow’ was recorded when durometer values (i.e., force measurements) of husks were 5.2, 5.5, and 3.4 N, respectively. Husk softening was also detected using the denting method, but the perception of denting did not consistently correspond with a specific husk hardness value. Of the three cultivars, ‘Kwik Krop’ kernels were the most difficult to visually sort into light, medium, and dark colors. Kernel LCH sum (L* + chroma + hue angle values), measured by a handheld spectrophotometer, provided a reliable color classification for all black walnut cultivars in which light kernels had LCH sums ≥150, medium kernels had sums of 149 to 126, and dark kernels had values ≤125.
Scott A. Brawner and Michele R. Warmund
Scott A. Brawner, Michele R. Warmund, and Mark V. Coggeshall
A study was conducted to: 1) evaluate the use of a durometer for determining husk softening and the date of black walnut harvest and 2) elucidate the relationship between husk hardness, kernel color and weight, and date of harvest. Thirty nuts were randomly collected weekly from mature `Sparrow', `Emma K', `Kwik Krop', and `Football' trees from 1 Sept. to 13 Oct. 2004. Husk denting, hardness, and color measurements were recorded immediately after harvest. Husk denting is the method commonly used by growers to determine the optimum time of harvest. Nuts were then hulled within 48 hours and the in-shell fresh weights were recorded. After drying under natural conditions for 5 weeks, kernel color and weights were assessed. On 15 Sept., 99% of `Sparrow' husks dented with a mean durometer value of 54. On 29 Sept., ≥99% of `Emma K' and `Kwik Krop' husks dented with mean durometer values of 63 and 68, respectively. By 13 Oct., 80% of `Football' husks dented with a mean durometer value of 74. From the first harvest date to the time of maximum denting, kernel weight and color (L*, hue values) of `Sparrow' and `Emma K' generally increased. The L* and hue values of `Kwik Krop' were inversely related to increased kernel weight over time. Kernel color of `Football' remained relatively constant as kernel weight increased over time.