Exported walnuts often require bleaching, and the cost of this process has significantly increased compared to untreated walnuts. The bleaching method for walnuts is outlined below:
First, the green skin needs to be removed. After harvesting and transporting the walnuts, they are typically turned on bamboo rafts while being peeled. However, this traditional method can lead to serious surface contamination and a decline in quality. To address this, a more efficient technique involves treating the walnuts with 5000 ppm ethylene. The nuts are fully immersed and placed in a controlled environment with a temperature of 30°C and a relative humidity of 80%. After five days, the peeling rate can reach over 95%, which not only reduces labor costs but also ensures a cleaner surface.
Next comes the bleaching and drying process. Once the walnuts are peeled, they are washed thoroughly to remove dirt. For bleaching, a small amount of warm water is mixed with bleaching powder, and then 80 kg of water is added per kilogram of the powder to create the solution. Alternatively, sodium hypochlorite (containing 10–15% available chlorine) can be used, with 30–40 kg of water per kilogram of the chemical. The cleaned walnuts are then submerged in the solution and stirred continuously for approximately 10–15 minutes. When the shells change from blue to white, they are removed immediately and rinsed with fresh water. Each batch can handle up to 80 kg of walnuts.
After rinsing, the walnuts are spread out thinly on foil or trays and dried. It's important to turn them regularly during the drying process. This usually takes about 8–10 days. The walnuts are ready when the kernel changes from milky white to golden yellow, and the middle diaphragm breaks. This thorough process ensures high-quality, visually appealing walnuts suitable for export.
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