Walnut Sizes
Walnut kernels are available in different sizes. The specifications are based on the "USDA Standards for Grades of Shelled Walnuts":
USDA Standard Sizes for Walnut Kernels
Walnut Halves
Description: 7/8 or more of the kernel is intact. 85 % or more of lot, by weight, are half kernels.
USDA Size Tolerances: No more than 5 % smaller than three-fourths halves of which no more than 1 % may pass through 16/64 inch (6.35 mm)
Walnut Pieces and Halves
Walnut Pieces and Halves (Halves and Pieces)
Description: 20 % or more of lot, by weight, are half kernels (7/8 or more of the kernel is intact).
USDA Size Tolerances: No more than 18 % shall pass through 24/64 inch (9.52 mm) round hole of which no more than 3 % may pass through 16/64 inch (6.35 mm) and of 3 % no more than 1 % may pass through 8/64 inch (3.18 mm) round screen hole.
Walnut Pieces
Description: Portions of kernels in lot cannot pass through 24/64 inch (9.53 mm) round openings.
USDA Size Tolerances: No more than 25 % shall pass through 24/64 inch (9.53 mm) round hole of which no more than 5 % may pass through 16/64 inch (6.35 mm) and of 5 % no more than 1 % may pass through 8/64 inch (3.18 mm) round hole included in the 5 %.
Walnut Small Pieces
Description: Portions of kernels in lot pass through 24/64 inch (9.53 mm) round openings but cannot pass through 8/64 inch (3.18 mm) round openings.
USDA Size Tolerances: 10 % will not pass through 24/64 inch (9.53 mm) round hole and 2 % pass through 8/64 inch (3.18 mm) round hole.
Typical industrial Sizes of Walnut Kernels
Walnut Medium Pieces
Although not covered in USDA Standards, Medium Pieces are a common size classification used in the California walnut industry. No less than 98 % may pass through a 32/64 inch (12.7 mm) screen. No more than 3 % may pass through 16/64 inch (6.35 mm) screen. No more than 1 % may pass through 8/64 (3.18 mm) screen.
Walnut Meal (double diced)
The smallest form of the California walnut comes in various consistencies ranging from a coarse meal to a fine powder. Use walnut meal to dust cakes, integrate into dough and batter, and for walnut compounds. Finely ground walnuts are incorporated into pastas, added to fillings, and used as a thickening agent in sauces.
Topping Pieces
Description: Portions of kernels in lot pass through 1/4 inch (6.35 mm) square screen hole or a 20/64 inch (7.64 mm) round screen hole.
Syrupers
Description: Portions of kernel in a lot pass through 3/8 inch (9.35 mm) square screen hole or 28/64 inch (11.11 mm) round screen hole.
In-shell Walnuts
Walnuts with a perfect shell are predetermined to be sold as in-shell walnuts. These are sized as jumbo, large, medium or baby according to USDA standards.