Walnut crackers are any sort of tool used to break the thick shell of a walnut. There are two main varieties of walnut: English and black. English walnuts tend to have a softer shell that is fairly easy to crack with handheld, pliers-like tools. Black varieties are usually much tougher, the opening of which often requires complex levers or mechanized systems. Any tools that opens these nuts' shells can qualify as walnut crackers, no matter how rudimentary.
Walnuts are usually encountered by consumers in nutmeat form — as ready-to-eat or ready-to-use nut pieces. No nuts grow this way, however, as the meat is contained inside the hard shell of the nut. Walnuts are technically seeds, and the nutmeat is encased in a hard, wood-like pod on the tree. Ripe nuts fall to the ground, and are then either collected by people gathering nuts, or eventually reincorporated into the soil to sprout new trees. The tough shell protects the nutrient-rich nutmeat that will sustain the seedling as it grows.
Just as the shell protects the nut against predators and environmental degradation, so does it protect against easy human opening. Cracking walnuts with bare hands is often extremely difficult, but eating or cooking with walnuts requires that they be opened somehow. Walnut crackers are specially designed to pry shells open, revealing nut halves that can be removed and eaten with ease.
The most basic walnut crackers are little more than carved stands that hold the nuts in an end-up position. This allows for precise striking with a hammer, mallet, or other blunt object. Walnuts, like most types of nuts, crack the most evenly directly down their center line.
More advanced and commonly-used walnut crackers resemble pliers more than anything else. Two metal handles join at the top, each usually with an central indentation about the size of an average walnut’s diameter. Placing the walnut in the indentation and then squeezing down on the handles cracks the walnut. The more pliable the walnut’s shell, the lesser the required force. This type of walnut cracker usually works best for English walnuts.
Black walnut crackers usually involve a crank and lever. Most are made of metal, and require the nut to be placed between two screws or plates that must be cranked progressively closer and closer together until the built-up pressure cracks the shell. Antique models usually incorporate large crank handles, while more modern innovations use simple push-levers.
Commercial walnut farms and mass-cracking operations often need more specialized tools for efficiency’s sake. Professional-grade walnut crackers usually bear little resemblance to personal or handheld tools. When hundreds of thousands of walnuts must be shelled, they are usually fed through precise hulling machines or pressed between cracker plates. Specialized machines separate the nutmeat from the hull, and quality control specialists usually sift through the final product to remove bits of shell that may have slipped through before the nuts are packaged for sale.
English walnuts, despite their name, are not native to England. They are indigenous in much of central Asia, particularly China, but quickly spread eastward, then westward, following ordinary routes of ancient trade. These walnuts are the most popular in Western markets, and are characterized by a light brown shell that is tough, but not impossible to open.
The black walnut is a related North American species that grows in limited regions, most prominently in the American South. This walnut variety has an extremely durable outer shell that is often prized for its use in abrasive cleaning scrubs. Opening a black walnut is usually a much more complex endeavor.