They are not the easiest nut to crack, but the flavor of black walnuts is delectable enough to be worth the considerable effort required to get the nuts from their shells. It can be a messy job, and walnut hulls stain, so wear gloves and old clothes for de-hulling. Gather walnuts in the early fall when they are falling from the trees and husks are still green. Blackened husks may have deteriorated too much for optimum flavor of the nutmeats inside.
Remove the yellowish green husks---the messiest part of the job---by hammering all around on the hull to loosen. With large quantities of nuts, it is helpful to spread them on the ground and drive over them at this stage; or use a portable cement mixer, corn sheller or even an old washing machine to tumble and bang them around. The main thing is to get the outer shell off before it deteriorates and spoils the nuts.
Examine each de-hulled nut for signs of insects. The University of Minnesota Extension Service suggests dropping nuts into a bucket of water to test for evidence of invasion by walnut weevils and husk fly maggots. Good nuts will sink to the bottom, while damaged nuts tend to float.
Scrub the hulled nuts with a stiff scrub brush or wire brush to remove any remaining bits of hull from crevices, and allow the nuts to dry.
Cure the clean nuts in a cool, dark, but dry place like a basement or pantry for two weeks prior to long term storage.
Store cured nuts in a cool but well ventilated area. They need relatively high humidity, but should be kept in wire baskets or other container allowing good air circulation, so they will not mold.
Prepare nuts for shelling by first dampening them sufficiently to prevent shattering of the shells. Do this by placing a dampened towel over the top of the nuts and removing them one at a time to crack.
Use a walnut cracker to break the shells, and then pick out the nutmeats with a nut pick.
Eat nuts raw or use in any recipe calling for walnuts. Be aware that black walnuts are strongly flavored, so add sparingly or use in combination with milder English Walnuts.