According to the classification, light walnut kernels are more valuable and their market value is much higher. Many recyclers encounter or notice a dark kernel during recycling. This raises questions: what determines the color of the kernel, how to avoid darkening and how to whiten the kernel of a walnut.
To a greater extent, the color of the kernel depends on the type of nut, but there are also external factors.
Green walnut peel paints hands dark and it is very difficult to wash them later. In the regions where the nut grows on every corner, they know about it from childhood. These dyes (iodine and juglone) are able to seep into the nut and turn the kernel into a darker color. Therefore, in order to avoid darkening of the kernel, the ripe nut must be cleaned of the green pericarp as soon as possible. It is especially important to remove a nut that has fallen to the ground. In large orchards, at the first signs of maturity, the nut is harvested and sent for cleaning, where the pericarp is removed and the remains of iodine, juglone and dust are washed off.
The color of the kernel also depends on the quality of storage. In-shell nuts should be stored in a dry, well-ventilated area, avoiding sunlight, at temperatures from -5 to +10 and humidity no more than 50%. You can store the walnut in cardboard or wooden boxes, in mesh bags up to 20 kg. With small volumes, peeled walnuts should be stored in refrigerators or freezers. On an industrial scale, the kernel is stored in vacuum packaging.
Opinions differ over the sun’s influence on kernel color. The peel and kernel of the walnut contains tannins such as gallic acid and tannins. Under the influence of the sun and oxygen, they oxidize and turn brown. Therefore, it is better not to leave the nut in the sun. If there is no way to hide the nut in a dark place, you need to at least remove it in the shade.
There is no natural way to bleach walnut kernels. Chemical methods to bleach the kernel are unsafe and affect the quality of the kernel. The bleached kernel will no longer be considered environmentally friendly, and the manufacturer of such a kernel is unlikely to eat it himself. You can get the lightest kernel possible only by preventing its darkening. Some manufacturers resort to blanching the walnut, that is, removing the skin from the kernel. This method is used in cases where the nut after all stages of processing looks “beaten” or the kernel will be used in confectionery.
If you are planning to plant your own nut, it is important to pay attention to the variety you choose, as there are varieties with a lighter kernel.
A common cause of dark kernels is late harvesting. The longer the ripe nut is in the pericarp, the more dyes penetrate into it.
Proper storage affects not only the color of the kernel, but also its quality and the ability to store for a long time without losing its useful properties.
By protecting the walnut from the sun’s rays (after harvesting), you protect it from oxidation and, as a result, darkening of the kernel. By adhering to these rules, you will get a light, high-quality kernel that will be well and long-term stored and which can be sold at a profit.