The walnut hull is the fleshy, green outer layer surrounding the hard shell of the nut. Prompt removal is necessary for both quality and cleanliness. This protective casing contains high concentrations of the natural dye juglone and various tannins. If hulls remain too long, these chemicals can seep into the shell, causing severe discoloration and sometimes imparting an unpleasant flavor to the nutmeat. While separating the hull from the shell is inherently messy due to the pigments, using correct methods and precautions can mitigate staining and ensure the nuts cure properly.
Preventing Stains and Handling Precautions
Working with walnut hulls requires preparation to prevent indelible staining caused by juglone, a chemical pigment that binds strongly to organic materials. Thick, durable gloves, such as heavy-duty rubber or nitrile, are mandatory to create an effective barrier. Standard latex gloves often fail to prevent the dark pigment from soaking through to the skin, where the stain can last for weeks.
Juglone is also a mild irritant that can cause localized skin reactions, sometimes leading to itching or blistering. Wearing long sleeves, old clothing, and eye protection provides defense against accidental splashes of the caustic hull juice. The handling area should be outdoors and away from concrete or stone surfaces, as the juice will leave lasting dark stains. Children should be kept away from the hulling process due to the staining and irritant risks.
Manual and Mechanical Removal Techniques
Once safety preparations are complete, several techniques can separate the hull from the hard shell, ranging from manual methods to mechanical abrasion. A simple manual approach is to place the nuts on a hard surface, such as asphalt, and stomp on them while wearing sturdy boots. This action crushes the soft hull, allowing the hard shell to pop out with minimal damage.
For larger batches, mechanical abrasion uses the nuts’ friction to strip the hull away. This is achieved by placing nuts in a heavy-duty container, like a metal garbage can, with water, and using a paint-stirrer attachment on a powerful drill to aggressively agitate the mixture. The swirling nuts rub against each other, tearing off the outer husk and reducing the process from hours to minutes.
Controlled Manual Hulling
A more controlled manual method for smaller quantities involves using a specialized tool or a heavy object to roll over the nuts. Placing the walnuts on a solid base and rolling them with a heavy plank or a section of two-by-four lumber shears off the hull without cracking the shell.
Retting Method
Alternatively, the retting method involves soaking the nuts in water or piling them in a damp location for a few days to naturally soften the hulls. This method requires careful monitoring to ensure the hulls soften enough for easy removal. If not monitored, mold or rot can develop quickly, which can ruin the nutmeat inside.
Immediate Steps After Hull Separation
Once the hull is removed, the shelled nuts are still coated in sticky, dark residue. The immediate next step is a thorough washing to remove all remaining hull fragments, juice, and juglone residue that could affect the nut’s flavor during storage. This washing can be done vigorously with a strong jet from a garden hose or by agitating the nuts in multiple changes of clean water until the water runs clear.
During washing, the float test is a practical quality control method where nuts are submerged in water. Any nuts that float are likely unfilled, rancid, or damaged, and should be discarded, as good-quality nuts will sink. After washing, inspect the nuts closely for signs of shell damage or persistent mold, and remove any questionable nuts from the batch.
The clean nuts must then be prepared for the final curing stage, a gradual drying process that develops flavor and ensures long-term storage stability. To begin, spread the nuts out in shallow layers, no more than two or three nuts deep, on a wire screen or a surface allowing maximum air circulation. They should be placed in a cool, dry, and well-ventilated location, such as a shed or garage, and kept out of direct sunlight.