Walnut harvesting processing technology

When the walnut peel's green skin turns from green to yellow, some of the peels are cracked at the top, easily peeled off, the seed is full, the young embryos are mature, and the cotyledons are hardened, it is the best harvest time for walnuts. At this time, the flavor of the nuts is strong and the quality is the best. However, improper post-harvest treatment will also greatly reduce the quality of walnuts.

1. Harvesting method

The walnut harvesting methods include manual harvesting and mechanical harvesting. The former is a commonly used method in China. Its characteristic is that when the fruit is ripe, it is used to hit the branches where the walnut is located or directly shoot down the fruit with a bamboo pole or a long wooden pole with elasticity. Manual harvesting should be performed from top to bottom and from inside to outside, so as not to damage the shoots and affect the output in the coming year. Mechanized harvesting equipment includes vibrating fruit-dropping machines, sweeping-collecting machines and picking-up and sorting machines. The operating procedure is to shake the walnuts to the ground with a vibrating fruit-dropping machine, and then the sweeping-collecting machine will concentrate the ground walnuts into strips. Finally, it is picked up by picking and sorting machine and is simply selected and packed. Because the maturity period of the fruit on the same walnut tree is not exactly the same, therefore, when using mechanized harvesting, it must be within 10 days to 20 days before the harvest to spray 4 times the tree mass fraction of 5×10. 2×10 negative third power ethephon was ripened to make it mature. The mechanically harvested walnut peels are easily peeled off and the fruit surface is less polluted, but the disadvantage is that a large number of leaves fall off earlier and weaken the tree vigor.

2. Remove the skin

It was determined that the freshly harvested walnuts had a water content of 40% to 45%, and nuts had a water content of 20% to 25%. Such a high moisture content can easily make the walnuts rot and spoil after harvesting. Therefore, after the walnuts are harvested, the green peel treatment should be performed in time. Typical methods for removing walnut peels include stack peeling, chemical peeling, and mechanical peeling.

(1) Stacking, peeling, and harvesting Walnuts shall be transported to outdoor shade or indoors in a timely manner after harvesting, and piled in heaps at a thickness of about 50 cm. The piles are too thick to be rot and should not be exposed to sunlight. If a layer of 10cm thick hay or dried leaves is added to the fruit heap, the temperature inside the heap can be increased, and the nuts can be cooked later to speed up the peeling. Generally stacking 3 days ? 5 days, when the peel from the shell or cracking of more than 50%, you can use wood stick knock peeling. The unpeeled walnut fruit can be stacked for several more days until it is fully peeled. When stacking, do not make the black peel dark, or even rot, so as not to infiltrate the nut inside the shell to contaminate the nuts and reduce the quality and commercial value of the walnut nuts.

(2) After peeling, the walnut peel is immersed for 0.5 min in the negative 3rd power of 3×10×3×10 negative 3rd power, and then stacked in the shade at a thickness of about 50cm. At a temperature of 30°C and a relative humidity of 80% to 95%, the peel rate can be as high as 95% or more in about 5 days. If the stack is covered with a layer of hay about 10cm thick, it can be peeled off in about 2 days. According to the determination, the primary fruit rate of this peeling method is 52% more than that of stacking method, and the degeneration rate of nuts is reduced to 1.3%, and the fruit surface is clean and beautiful. The length of the ethephon ripening time is related to the quality of the drug solution and the maturity of the fruit. If the fruit maturity is high, the quality of the drug solution is low and the ripening time is short.

(3) Mechanical peeling method According to the rubbing principle, the walnut with the peel is worn and rubbed between the rotating grinding disc and the hard wire brush, so that the walnut peel is separated from the nuts. If walnut walnut has low water content, shrinking kernels, and large rubbing force, it can easily damage the kernels when peeling. Therefore, when removing walnut peels by mechanical peeling, they must be removed within 1 day or 2 days after harvesting.

3. Rinsing treatment

After the walnuts have been removed from the green skin, the dirt on the nuts, the remaining rotten skin, and the branches and leaves can be removed by washing. Cleaning methods include manual cleaning and mechanical cleaning. The method of manual cleaning is to basket the peeled nuts, put the baskets in a sink or flowing water, and scrub them with a bamboo broom. When washing in the pool, it should be replaced with fresh water in a timely manner, each washing about 5min, the washing time should not be too long, so as to prevent the dirty water infiltrated into the shell contaminated nuts. With mechanical cleaning, its ergonomics are three to four times that of manual cleaning, and the walnut yield will also increase by about 10%.

In order to make the finished walnut appearance smooth, clean and consistent in color, the walnuts are often bleached after washing. The specific method is to dissolve the bleaching essence (containing 80% of sodium hypochlorite) into water 5 times to 7 times in the ceramic jar, then put the cleaned walnut into the cylinder, so that the bleach is immersed in the nuts and stirred with a wooden stick. 3min?5min. When the walnut shell surface turns white, remove it immediately and rinse it twice with water. As long as the bleach is not turbid, it can be continuously rinsed. Generally, one batch of bleach can be rinsed with 7 batches of 8 batches of walnuts. When rinsing with bleaching powder, first dissolve 0.5kg of bleached warm water, 3kg to 4kg, remove the residue, then mix the water in a ceramic tank with 30kg to 40kg of bleaching solution, and put the washed walnut in bleach. Stir 8min?10min. When the surface of the nut turns white, remove it, wash it, and dry it. The used bleaching solution plus 0.25 kg of bleach can continue rinsing, and 40 kg of walnut nuts can be rinsed each time.

4. Dry processing

The dried walnut nuts are naturally dried and artificially dried.

(1) Naturally washed and washed nuts should be dried on bamboo foil or sorghum stalk foil for half a day until most of the water evaporates and then spread on the foil for drying. The thickness of the booth should not exceed two layers. If it is too thick, it will be prone to heat, and the kernels will be degraded and not easily dried. When it is dry, it must be turned frequently. Avoid rain and moisture at night. Do not expose it to sunlight so as to avoid cracking of the shell and deterioration of the nuts. It usually takes 5 days to 7 days to dry.

(2) Compared with natural air drying, artificial drying has higher equipment and installation costs for manual drying, and the operation technology is more complicated and costly. However, artificial drying has unparalleled advantages of natural drying. It is the development direction of walnut nuts. At present, China's artificial drying equipment, according to the thermal effect of drying, is generally divided into convection drying equipment, heat radiation drying equipment and induction drying equipment of three types. In addition, there are also batch-type drying chambers and continuous-channel drying chambers as well as low-temperature drying chambers and high-temperature drying chambers. The heating medium used is steam, hot water, electric energy, flue gas and so on. Intermittent drying chambers generally use steam, electrical heating, and continuous channel drying rooms use infrared heating. Electromagnetic induction drying is not widely used at present. The most used in production is drying ovens and drying rooms. It uses stove heating and heat convection to complete the heat conduction.

5. Walnut grading

The quality of walnut nuts is of great concern to producers, operators, consumers and foreign trade departments. The quality of different nuts has different prices. The new quality grades are divided into four grades: Special Grade, First Grade, Second Grade and Third Grade. Each grade requires full maturity of nuts, clean shell surfaces, tight sutures, no exposed kernels, insects, oil, mildew, etc. Odor, no impurities, no harmful chemical bleaching.

(1) Super walnut fruit shape is uniform, the shape is the same, the shell is naturally yellowish-white, the kernels are full, the color is yellow and white, and the astringency is light; the diameter of the nut is not less than 30mm, the average single fruit quality is not less than 12.0g, and the kernel rate reaches 53.0%, the empty shell fruit rate does not exceed 1.0, the broken fruit rate does not exceed 0.1%, the moisture content is not higher than 8.0%, no black spot fruit, easy to take the whole kernel; the crude fat content is not less than 65.0%, the protein quality reaches 14.0 %.

(2) The primary walnut fruit shape is basically inconsistent, the kernel rate reaches 48.0%, the empty shell fruit rate does not exceed 2.0%, and the black fruit rate does not exceed 0.1%. Other indicators are the same as the special grade fruit indicators.

(3) The shape of the secondary walnut is basically the same, the shell is naturally yellowish-white, the kernels are full, yellowish-white, and astringent; the diameter of the nut is not less than 28.0mm, the average fruit weight is not less than 10.0g, and the kernel rate is reached 43.0%, the empty shell fruit rate does not exceed 2.0%, the damaged fruit rate does not exceed 0.2%, the moisture content is not higher than 8.0%, the black fruit rate is not more than 0.2%, and it is easy to take half; the crude fat content is not less than 60.0% The protein content reached 12.0%.

(4) The third-level walnuts have no fruit shape requirements, the shell is naturally yellowish-white or tan, and the nuts are full, yellowish-white or light amber, slightly astringent; the nut diameter is not less than 26.0mm, and the average fruit quality is not lower than 8.0g, the kernel rate reaches 38.0%, the empty shell fruit rate does not exceed 3.0%, the broken fruit rate does not exceed 0.3%, the moisture content does not exceed 8.0%, and the black fruit rate does not exceed 0.3%, it is easy to take a quarter Ren; crude fat content of not less than 60.0%, protein content of 10.0%.

After classification, the walnuts should be packed in dry, firm, clean and hygienic sacks. Each bag should be about 45kg in size. The purse must be tightly sewn with needles and the lot number must be marked in the upper left corner of the package. Walnuts with shells thinner than 1mm can be packed in cartons. During the transportation process, rain, pollution, and violent collisions should be prevented.

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