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Missouri Environment & Garden



AUTHOR

Michele Warmund
University of Missouri
Division of Plant Sciences
(573) 882-9632
warmundm@missouri.edu

Black Walnuts: Pick Them and Clean Them Up Quickly

Michele Warmund
University of Missouri
(573) 882-9632
warmundm@missouri.edu

Published: October 1, 2009

Now is the time to take advantage of the wild black walnuts as trees are shedding their nuts rapidly. Since there are over 97 million wild black trees in Missouri, there is likely one near you! While commercial producers typically harvest with a mechanical tree shaker, homeowners can enjoy the nuts picked from the tree or from the ground after falling from the tree. The highest quality nuts are those still attached to the tree. To determine the right time to harvest nuts from the tree, a “dent test” can be used. This is performed by holding a walnut and depressing the husk with the thumb. When more than 75% of the black walnut husks dent, the walnut tree is ready for harvest. Research at the University of Missouri has shown that husk softening is associated with walnut maturity. An instrument, such as the durometer, which measures husk hardness, is another way to determine the harvest date for black walnuts. However, if you are too late to harvest the nuts from the tree, it is important to collect the nuts soon after they drop to enjoy them before squirrels find them.

Another reason to harvest them when the hulls are softening and green is that the kernels will be mature and flavorful, but not dark in color or taste rancid. With a two week delay in husk removal, kernels turn black and the less desirable flavors will have developed. Not only is it important to collect the walnuts quickly, but it is also important to remove the husks as soon as possible after harvest. For large scale production, mechanical hulling (husk removal) is used, but homeowners often use other creative methods such as running over the nuts with a vehicle or using grinders or other abrasive means to remove the husks.

Once husks are removed, walnuts are hung in bags and dried for about five weeks. Onion bags or other loose-woven bags that permit air movement are ideal. After the nuts have dried, either crack them immediately or store them at 32 to 40ºF. Before cracking, inspect the shells to make sure that there are no fissures or cracks in the shell. Walnuts with cracked shells are often infected with microorganisms and should be discarded. Bright yellow, blue streaked, or black kernels should not be consumed. For black walnuts with sound shells, heavy duty crackers are needed to break open the thick shells. An example of such a nut cracker can be found at: http://www.nutgrowing.org/. After cracking, walnuts for immediate use can be placed in an airtight container in the refrigerator or they can be stored in the freezer until next year’s harvest. To enjoy black walnuts year round, try some of the recipes at: http://www.black-walnuts.com/

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REVISED: August 1, 2012