Light-colored black walnut kernels have a milder flavor than dark ones. If you prefer light-colored kernels, hull the nuts as soon as they drop from the tree. Allowing the hulls to partially decompose before hulling causes a discoloration of the kernels.
The hulls are thick and fleshy at maturity. They can be mashed and removed by hand, but mechanical devices such as a corn sheller make the job easier.
After hulling, wash the nuts thoroughly and spread out away from sunlight to dry for 2 to 3 weeks. Then store in a cool, dry place.
Kernels that have been tempered before the shell is cracked are easier to remove. Soak the nuts in water for 1 to 2 hours, drain, then keep in a closed container for 10 to 12 hours. The kernels will absorb enough moisture to become tough, yet will remain loose in the shell.