Black walnuts are desirable tree nuts that ripen in the late summer and early fall, from August to early October. Black walnuts should be allowed to to ripen hanging on the tree in order for their flavor and texture to fully develop. After harvest they are stripped of their outer husk, dried and cured before they are shelled and consumed. Two pounds of black walnuts without the husks or shells yield about one cup of walnuts.
Ripeness and Harvesting
When black walnuts become ripe, their husk color changes from green to a yellow-green. Nearly every part--except the nut meat--of a black walnut can make indelible stains on gloves when harvesting. Press down on the skin if the husk with your thumb. If ripe, the pressure of your thumb will leave an indentation. Test the walnuts every week until you see the indentation. Walnuts on the same tree will ripen within four to six weeks of each other. Harvest the ripe nuts by pulling gently. Nuts too high in the canopy to reach can be picked from the ground after they fall from the tree.
Walnuts must be husked after harvest to prevent the decomposing outer husk from discoloring and ruining the flavor of the nut inside. The outer husks are tough. Hulling black walnuts can make a mess; the husks will stain anything it comes into contact with. Wear eye protection, gloves, old clothes you don't mind getting stained. Cover all working surfaces with at least 10 layers of newsprint or thick plastic sheeting. To remove the husk from dry nuts, apply pressure to the ends of the nut to crack it. Use a hammer to pound each end or use pliers to apply pressure until it cracks. Wash the unshelled nuts in clear clean water in a bucket or a stainless steel or dark sink. The black walnut shells can also stain light colored porcelain if the finish has worn areas. Walnuts can be infected with insects. A quick and easy check on this is to put the walnuts in a bucket of clean water. The nuts that have not been infested will sink; any nuts that float a should be thrown away.
Curing Black Walnuts for Use
After you remove the husks, cure the nuts to prepare them for storage and to allow the deep walnut flavor to develop. Layer the walnut no more than three nuts deep in a well ventilated container such as a loose woven or metal basket. Store for two weeks in a cool, dry area that gets no direct sunlight. After two weeks, crack open a walnut; if the nut beaks crisply when snapped in half they are ready for storage and consumption. If it still seems moist, give the nuts another week to cure and test again. After they are cured, store the nuts at 60 degrees F or less in an area with fresh air flow to prevent mold.