The black walnut (Juglans nigra) is one of the most valuable timber trees in Iowa. It is also a valuable nut tree.
Harvesting, hulling, cleaning, and cracking black walnuts requires considerable labor and patience. Those efforts, however, are rewarded when fudge, brownies, candies, and cakes are made from Iowa-grown black walnuts.
When to Harvest
Walnuts ripen in the fall. As the fruit matures, the hull softens and changes from solid green to a yellowish color. The fruits are mature and ready for harvest as soon as the hull can be dented with your thumb. In Iowa, nuts typically mature in mid to late September.
How to Harvest
The best quality nuts are obtained by picking or shaking the mature nuts from the tree. Most individuals, however, gather the mature nuts as they drop to the ground. . Before you spend a lot of time gathering nuts, it's a good idea to crack a few to make sure the kernels are full. Nuts occasionally fail to fill or have small, shrunken kernels. Nut crops vary from year to year. A tree that produced bushels last year may have many or few nuts this year.
How to Hull Walnuts
The nuts should be hulled immediately after they have been harvested. If the hulls are allowed to remain on for any length of time, the juice in the hull will discolor the nut meats and make them strong-tasting. The stain also discolors skin, clothing, concrete, and anything else that it touches.
There are various ways and devices to hull walnuts -- a cement mixer, corn sheller, automobile wheel, and squirrel cage are possibilities. Hulls can also be removed by stomping the nuts underfoot or pounding with a hammer. After hulling, thoroughly wash the nuts to remove hull debris and juices. Small quantities can be washed in a large bucket or tub. At this time, the good nuts can be sorted from the bad ones. Unfilled nuts float while filled nuts sink. (Rubber gloves should be worn when hulling and cleaning to prevent staining of the hands.)
After washing and sorting, allow the nuts to dry for two or three weeks. An excellent way to dry nuts is on a wire screen. Spread the nuts in shallow layers (no more than three nuts deep)and dry them in a cool, dry, well-ventilated area. A shed or garage is usually a good place to dry walnuts.
The black walnut has one of the toughest and thickest shells to crack. While nuts can be cracked with various tools, the hammer and nutcracker are most commonly used. The hammer method involves placing the nut, pointed end up, on a hard surface and striking the point with the hammer until it weakens and splits into sections along its axis. Several nut-cracking tools are also available.
When cracking nuts, shattering of the kernels is often a problem. Shattering can be reduced by soaking the nuts in water for 1 or 2 hours before cracking. The soaking process allows the kernels to absorb enough moisture to become somewhat flexible, resulting in larger kernel pieces. The kernels are extracted from the nutshell with a pick and a pair of pliers.
The oils in walnut kernels will turn rancid if nuts are stored improperly. After the kernels have been removed, place them in a plastic bag and store them in the freezer. The nutmeats will keep almost indefinitely when stored in the freezer. Kernels can be stored for short periods in the refrigerator.