A Detailed Guide to the Correct Methods of Walnut Grading and Packaging

  1. Nut grading standards and packaging. Sun-dried walnuts must be graded, because the quality of walnut nuts is of great concern to producers, traders, consumers and foreign trade departments, so nuts of different quality fetch different prices. Walnut nut quality is divided into 4 grades: special grade, first grade, second grade and third grade. Every grade requires that the nuts be fully mature, with clean shells, tightly closed sutures, no exposed kernels, insect damage, oil leakage, mould or off-odours, no impurities, and no harmful chemicals.

  (1) Special-grade walnuts: uniform in size and consistent in shape, with naturally yellow-white shells, plump kernels of yellow-white colour and mild astringency; nut transverse diameter not less than 30 mm, average single-nut weight not less than 12.0 g, kernel yield reaching 53%, empty-shell nut rate not more than 1%, damaged-nut rate not more than 0.1%, moisture content not higher than 8%, no black-spot nuts, and easy to obtain whole kernels; crude fat content not less than 65%, protein content reaching 14%.

  (2) First-grade walnuts: basically consistent in shape, kernel yield reaching 48%, empty-shell nut rate not more than 2%, black-spot nut rate not more than 0.1%, and other indicators the same as those for special-grade nuts.

  (3) Second-grade walnuts: basically consistent in shape, with naturally yellow-white shells, relatively plump kernels of yellow-white colour and mild astringency; nut transverse diameter not less than 30 mm, average single-nut weight not less than 10 g, kernel yield reaching 43%, empty-shell nut rate not more than 2%, damaged-nut rate not more than 0.2%, moisture content not higher than 8%, black-spot nut rate not more than 0.2%, and easy to obtain half kernels; crude fat content not less than 60%, protein content reaching 12%.

  (4) Third-grade walnuts: no shape requirement, with naturally yellow-white or yellow-brown shells, relatively plump kernels of yellow-white or light amber colour and slightly astringent; nut transverse diameter not less than 26 mm, average single-nut weight not less than 8 g, kernel yield reaching 38%, empty-shell nut rate not more than 3%, damaged-nut rate not more than 0.3%, moisture content not higher than 8%, black-spot nut rate not more than 0.3%, and easy to obtain 1/4 kernels; crude fat content not less than 60%, protein content reaching 10%.

  Graded walnut nuts should be packed in dry, sturdy, clean and hygienic gunny sacks, each holding about 45 kg, with the opening sewn tightly with needle and thread, and the batch number marked in the upper left corner of the bag; walnuts with shells thinner than 1 mm may be packed in cardboard boxes. During transport, they should be protected from rain, contamination and violent impact.

  2. Kernel grading standards and packaging

  (1) Kernel extraction methods. There are two ways to extract walnut kernels: manual extraction and mechanical extraction. In China, the manual cracking method is mostly used. Walnut kernels are divided into dry-cracked and wet-cracked types. So-called dry cracking means cracking the nuts after the walnuts have been fully air-dried to reduce their moisture (generally below 5%); the kernels from this method have dry, white broken surfaces, commonly called "yang cha" (sun cracks), and those that are crisp and glossy are considered the best, and are very popular with overseas customers; so-called "wet cracking" means cracking the nuts before the moisture of the walnuts has been reduced. Wet-cracked walnut kernels have dull broken surfaces with a phenomenon similar to oil sheen, are not crisp and are grey and lustreless, commonly called "yin cha" (shade cracks). Such walnut kernels deteriorate more easily. However, for reasons of storage and so on, dry-cracked kernels whose broken surfaces show oil sheen do not fall into this category. When cracking nuts, care should be taken to place the suture parallel to the ground, to apply force evenly, and not to strike hard or repeatedly, so as to obtain whole kernels as far as possible. To reduce contamination of the kernels after the nuts are cracked open, the work area must be cleaned before cracking and kept hygienic; cracking directly on the ground is not allowed. After the nuts are cracked, first put them into clean baskets or pile them on plastic sheeting, and shell out the kernels after cracking is finished. When shelling, it is best to wear clean gloves, put the shelled kernels directly into clean containers or plastic bags, and then grade and pack them. Mechanical shell cracking usually uses a nut press to crush the shells and extract the kernels, and its efficiency is far higher than manual cracking. Taking Australia as an example, its mechanical kernel extraction is a flow-line production operation system including nut grading, orientation, crushing and shell cracking, shell-kernel separation, and kernel grading and packaging, which greatly improves the grade and profitability of walnut kernels.

  (2) Kernel grading standards and packaging

  According to the colour and degree of wholeness of the walnut kernels, walnut kernels are divided into eight grades, and in industry terminology a "grade" is called a "lu" (road).

  White first road: 1/2 kernels, light yellow;

  White second road: 1/4 kernels, light yellow;

  White third road: 1/8 kernels, light yellow;

  Light first road: 1/2 kernels, light amber;

  Light second road: 1/4 kernels, light amber;

  Light third road: 1/8 kernels, light amber;

  Mixed fourth road: broken kernels, kernel colour light and uniform;

⟧   Dark third road: broken kernels, kernels dark in colour.

  When grading walnut kernels, besides paying attention to kernel size and colour, the kernels are also required to be dry, thick, plump, free of insect damage, free of mould and deterioration, free of off-odours and free of impurities. Walnut kernels of different grades have different export prices, with white first road the highest and light first road next, but there are not many kernels that fully meet these two types. The kernel products China exports in large quantities are the four grades of white second road, white third road, light second road and light third road, while kernels of the mixed fourth road and dark third road types are all used for domestic sale and processing.

  Walnut kernels are generally packaged in cardboard boxes or wooden boxes. The wood used for kernel packaging boxes must not have off-odours; generally each box holds a net weight of 20-25 kg of kernels. Moisture-proof measures should be taken during packaging, lining the bottom and sides of the box with moisture-proof materials such as cellophane; after packing, seal and bind immediately, and mark the weight, grade and address, etc.