Walnut Storage and Pretreatment

Walnut is one of the main dried fruits. Its nutritional value is high and it contains high oil, protein, vitamins and minerals. Walnut kernel is also a kind of tonic commonly used in traditional Chinese medicine, with qi and blood, moistening dryness, clearing the lungs and intestines. Deeply loved by consumers. Walnuts are distributed in various provinces in northern China. The main varieties include Shanxi Light-peeled Walnut and Spike-like Walnut Walnut, Hebei Luren Walnut, Shaanxi New Year Walnut, and Shandong Mapi Walnut.

(1) Storage characteristics Walnut is a kind of nut fruit with hard woody husk, so it is more resistant to transportation and storage. However, due to its high protein and fatty acid content in the kernel, improper storage can cause deterioration and loss of commercial value.

(2) Harvesting and storage

1 Harvesting walnuts must reach full maturity before they can be harvested. The main feature is that the exocarp is yellow from the green, some of the fruits are cracked on their own, and the wood peel is thin. The kernels are full of fat and have high fat content. If harvesting is too early, the peel will not peel easily, the seed will not be full, and the rate of the kernel will be low. And it is not resistant to hiding; if it is cracked, staying in the tree for too long will increase the chance of mold infection and cause moldy rot. Under normal circumstances, 80% of the whole tree can be harvested when it reaches full maturity.

The harvesting of walnuts is usually carried out during the white dew to the equinox season. A plastic film mat is placed under the tree, and a flexible bamboo raft is used to shoot fruit. If the walnut tree is sprayed with 500 mg/L ethephon solution at the end of March or early April, it can promote natural fruit drop and early harvest time, which is also conducive to mechanical harvesting.

2 Pre-storage treatment

a. Peeling walnuts that have not peeled off from the outer skin can be deposited and peeled, that is, the walnuts are piled in a cool place or indoors, covered with walnut leaves or grass insulation, and the accumulated thickness is about 60 cm. Generally, the green skin can be removed after 2-4 days. In addition, unpeeled walnuts can also be soaked in an ethephon solution of 3000-5000 mg/L for half a minute, then allowed to air dry, placed in a cool place or indoors, covered with walnut leaves or grass, and generally peeled off in 3 days.

b. Walnuts after rinsing and rinsing should be rinsed with fresh water within 3 hours. If the vascular bundles at the base of the walnuts shrink after a long interval, the moisture will immerse, causing the nuts to be easily discolored and rot. However, walnuts used for seeding cannot be rinsed, because moisture will penetrate the shell during the rinsing process and affect the germination rate.

c. Dried walnuts after drying were dried and spread on the mat to dry. During the drying process, it is necessary to pay attention to moisture, rain, and frequent turning. Meanwhile, the dried walnuts should not be stacked too thick to prevent the deterioration of the kernels caused by heat. After drying for 4-6 days in general, the walnut skin turns from milky white to light brown, and the knocking sound is loud, and it is easy to break and rupture when the diaphragm is broken by hand, indicating that the walnut has dried. In addition, drying can also be performed at a temperature of 40-50°C. However, during the drying process, care should be taken to ensure that the fruit color is uniform.

d. During the storage of walnuts, insects are prone to insect infestation. If walnuts of 3 volumes per 100 m before storage are fumigated with 15 kg of sulphur dioxide or 1.7 kg of chloropicrin for 24 hours, then storage can effectively prevent the occurrence of insect pests.

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