Red Walnuts are not genetically modified. Instead, they were created using natural methods of grafting Persian red-skinned walnuts onto larger and creamier English walnuts. To retain their red color, they should be shelled by hand. Machine shelling causes the red layer to dull and chip. These nuts are larger in size and the shells are a little harder than other walnut varieties, while their trees grow slower. Since there are limited amounts of producing trees, these rare walnuts are currently only found in high-end stores, some farmer’s markets, and online.
The red walnut, also known as a Livermore Walnut, was developed in 1991 at the University of California, Davis. Scientists at the university obtained a rare cultivar of walnut from the French National Institute of Agricultural Research collection. Through a controlled pollination experiment with a standard walnut cultivar, the Livermore red walnut was created.