Black walnut trees are prized for both their timber and their rich nuts. Black walnuts are produced on the tree in the late spring following flowering. They mature on the tree throughout the summer and early fall and are ripe for harvest when they fall to the ground or the outer hull can be dented with a thumbnail. Biological malformation, disease, insect or weather damage can all affect nut meat quality, and there are a few traditional methods for detecting this. Black walnuts can only be judged to be healthy once the hull is removed, so that is always a first step.
Things You'll Need
Rubber or latex gloves
Large bucket or sink of hot of water
Long dowel or wooden spoon
Walnuts in shell
Don waterproof gloves when working with black walnuts, as the indelible dye inside the hull will heavily stain anything it comes into contact with. Score the outer hull over a pile of newsprint, peel back the hull skin and discard in the trash.
Drop the dye-coated black walnut shell into a clean bucket or utility sink filled with hot water. Repeat the process for each walnut until you have a bucket of walnuts in ink-black water. Stir the bucket vigorously to agitate the nuts, dislodge any remaining bits of hull on the shell and lift the dye from the shells. Pour out the first rinse water and refill with fresh hot water. Soak the hulled walnut shells for a few minutes and rinse a third time if needed to remove any remainder of dye.
Allow the nuts to settle in the final rinse water for 10 minutes or so. Remove the few walnuts that remain floating and consider those that sink to be good nuts. Black walnuts that float are likely compromised in some way and should be set aside from the harvest to be checked by cracking or discarded entirely.
Feel the weight of many individual walnut shells in your hand after they have been hulled. Over time you will develop a sense of when a black walnut feels inordinately light in weight for its size and it can be set aside to be checked. If it turns out to be compromised, that is a sign that similarly lightweight nuts are not good or must also be checked.