Michigan State University Extension
Preserving Food Safely - 01600670
For best color and flavor, nuts such as black walnuts should be hulled soon after gathering. If not hulled quickly, the bitter fluid secreted in the hulls penetrates the nutmeat, discoloring nuts and impairing flavor. Also, leaving nuts in the hull encourages mold growth. Gloves should be worn to protect hands from the near-permanent stain secreted by the hull.
Once gathered, freshly fallen nuts must be "cured" or dried before storage as the nutmeats are still quite moist and almost juicy. Uncured nuts are difficult to crack and have a "green", bitter taste.
Before drying, immerse nuts in water and discard any diseased or rotten nuts which float to the top. This soaking also removes any accumulation of dirt or insects on the shell.